diff --git a/make_post_sell/lib/hex_color.py b/make_post_sell/lib/hex_color.py
index b2865e4..0267340 100644
--- a/make_post_sell/lib/hex_color.py
+++ b/make_post_sell/lib/hex_color.py
@@ -39,5 +39,5 @@ def color_scale(hex_str, scale_factor):
     g = int(clamp(g * scale_factor))
     b = int(clamp(b * scale_factor))
 
-    #return "#%02x%02x%02x" % (r, g, b)
-    return "#%02x%02x%02x" % (r, g, b)
+    # return "#%02x%02x%02x" % (r, g, b)
+    return f"#{r:02x}{g:02x}{b:02x}"
diff --git a/make_post_sell/lib/mail.py b/make_post_sell/lib/mail.py
index 78aff7c..a74fa79 100644
--- a/make_post_sell/lib/mail.py
+++ b/make_post_sell/lib/mail.py
@@ -43,7 +43,6 @@ def send_email(
     dkim_selector="",
     dkim_signature_algorithm="ed25519-sha256",
 ):
-
     # the `email` library assumes it is working with string objects.
     # the `dkim` library assumes it is working with byte objects.
     # this function performs the acrobatics to make them both happy.
@@ -106,13 +105,15 @@ def send_email(
 
 def send_pyramid_email(request, to_email, subject, message_text, message_html):
     """Thin wrapper around `send_email` to customise settings using request object."""
-    default_sender = "no-reply@{}".format(request.domain)
+    default_sender = f"no-reply@{request.domain}"
     sender_email = request.app.get("email.sender", default_sender)
-    subject = "{} | {}".format(subject, request.app.get("email.subject_postfix", request.domain))
+    subject = f"{subject} | {request.app.get('email.subject_postfix', request.domain)}"
     relay = request.app.get("email.relay", "localhost")
     dkim_private_key_path = request.app.get("email.dkim_private_key_path", "")
     dkim_selector = request.app.get("email.dkim_selector", "")
-    dkim_signature_algorithm = request.app.get("email.dkim_signature_algorithm", "ed25519-sha256")
+    dkim_signature_algorithm = request.app.get(
+        "email.dkim_signature_algorithm", "ed25519-sha256"
+    )
 
     send_email(
         to_email,
@@ -140,7 +141,7 @@ def send_verification_digits_to_email(request, to_email, raw_digits):
     raw_digits:
       the raw (unencrypted) digits the user may use to verify & authenticate.
     """
-    subject = "Verification Code | {}".format(raw_digits)
+    subject = f"Verification Code | {raw_digits}"
     message_text = WELCOME_1_TEXT.format(raw_digits)
     message_html = WELCOME_1_HTML.format(subject, raw_digits)
     send_pyramid_email(request, to_email, subject, message_text, message_html)
@@ -174,17 +175,13 @@ def send_purchase_email(request, to_email, products, total_cost):
             )
 
         product_text_list.append(
-            '<p><a href="{}">{}<br/>{}</a></p>'.format(
-                p.absolute_url(request), p.title, thumbnail
-            )
+            f'<p><a href="{p.absolute_url(request)}">{p.title}<br/>{thumbnail}</a></p>'
         )
     product_text = "<br/>".join(product_text_list)
 
-    message_text = PURCHASE_1_TEXT.format(
-        "%.2f" % total_cost, request.host_url
-    )
+    message_text = PURCHASE_1_TEXT.format(f"{total_cost:.2f}", request.host_url)
     message_html = PURCHASE_1_HTML.format(
-        subject, request.host_url, product_text, "%.2f" % total_cost
+        subject, request.host_url, product_text, f"{total_cost:.2f}"
     )
     send_pyramid_email(request, to_email, subject, message_text, message_html)
 
@@ -217,17 +214,15 @@ def send_sale_email(request, shop, products, total_cost):
             )
 
         product_text_list.append(
-            '<p><a href="{}">{}<br/>{}</a></p>'.format(
-                p.absolute_url(request), p.title, thumbnail
-            )
+            f'<p><a href="{p.absolute_url(request)}">{p.title}<br/>{thumbnail}</a></p>'
         )
     product_text = "<br/>".join(product_text_list)
 
     message_text = SALE_1_TEXT.format(
-        "%.2f" % total_cost, shop.absolute_sales_url(request)
+        f"{total_cost:.2f}", shop.absolute_sales_url(request)
     )
     message_html = SALE_1_HTML.format(
-        subject, shop.absolute_sales_url(request), product_text, "%.2f" % total_cost
+        subject, shop.absolute_sales_url(request), product_text, f"{total_cost:.2f}"
     )
 
     # send a separate email for each shop owner.
@@ -241,7 +236,7 @@ def send_invite_email(request, to_email, user, shop):
 
     request
       the request (of the successful log in attempt)
-   
+
     to_email
       the email address to send the shop invitation to.
 
@@ -251,7 +246,7 @@ def send_invite_email(request, to_email, user, shop):
     shop
       the shop the invitation is for.
     """
-    subject = "You have been invited to {}".format(shop.name)
+    subject = f"You have been invited to {shop.name}"
     join_link = request.route_url("join-or-log-in")
     message_text = INVITE_1_TEXT.format(user.email, shop.name, join_link)
     message_html = INVITE_1_HTML.format(subject, user.email, shop.name, join_link)
diff --git a/make_post_sell/lib/sanitize_html.py b/make_post_sell/lib/sanitize_html.py
index cc5dea3..d2a5c6a 100644
--- a/make_post_sell/lib/sanitize_html.py
+++ b/make_post_sell/lib/sanitize_html.py
@@ -62,13 +62,10 @@ def default_cleaner(tag_acl=None):
     # to get past bleach.
     # We will conditionally filter tags using BeautifulSoup.
     for tag_name in tag_acl.keys():
-
         # tag_name, for example "script".
 
         for attr_name, attr_value, allow_or_deny in tag_acl[tag_name]:
-
             if allow_or_deny == "allow":
-
                 # attr_name, for example "type".
                 # attr_value, for example "math/tex; mode=display".
 
@@ -84,7 +81,7 @@ def default_cleaner(tag_acl=None):
 
     # doesn't do anything, but i used to be able to pass it via constructor.
     # https://github.com/yourcelf/bleach-allowlist/blob/main/bleach_allowlist/bleach_allowlist.py
-    #cleaner.all_styles=all_styles
+    # cleaner.all_styles=all_styles
 
     # disable link_protection by default.
     cleaner.link_protection = False
@@ -122,17 +119,14 @@ def conditional_tag_filter(soup, cleaner):
 
     # for each tag_name in the tag_acl ...
     for tag_name in cleaner.tag_acl.keys():
-
         # find all the tags in the DOM that match the tag_name, for example "script".
         for tag in soup.find_all(tag_name):
-
             # tag is a BeautifulSoup tag object.
 
             # by default, assume we will extract tag (remove it from the DOM).
             extract_tag = True
 
             for attr_name, attr_value, allow_or_deny in cleaner.tag_acl[tag_name]:
-
                 # tag attr_name:
                 #
                 #   * "type"
@@ -151,10 +145,9 @@ def conditional_tag_filter(soup, cleaner):
                 #  * "allow"
                 #  * "deny"
 
-                log.info("{} {} {}".format(attr_name, attr_value, allow_or_deny))
+                log.info(f"{attr_name} {attr_value} {allow_or_deny}")
 
                 if allow_or_deny == "allow":
-
                     if tag.attrs.get(attr_name) == attr_value:
                         # this tag attr_name/attr_value is whitelisted.
                         # do not extract tag (remove it from the DOM)
@@ -175,7 +168,6 @@ def conditional_tag_filter(soup, cleaner):
 
 
 def protect_links(soup, cleaner):
-
     for a_tag in soup.find_all("a"):
         uri = miniuri.Uri(a_tag.attrs.get("href", ""))
 
diff --git a/make_post_sell/models/coupon.py b/make_post_sell/models/coupon.py
index 862e09c..78e55de 100644
--- a/make_post_sell/models/coupon.py
+++ b/make_post_sell/models/coupon.py
@@ -50,9 +50,7 @@ class Coupon(RBase, Base):
     description = Column(Unicode(256), nullable=False)
 
     # the type of action that this coupon applies to a cart.
-    action_type = Column(
-        Enum(*COUPON_ACTION_TYPES, name="action_type"), nullable=False
-    )
+    action_type = Column(Enum(*COUPON_ACTION_TYPES, name="action_type"), nullable=False)
     action_value = Column(BigInteger, nullable=False)
 
     # The amount of times this code may be used.
@@ -77,13 +75,17 @@ class Coupon(RBase, Base):
     shop = relationship(argument="Shop", uselist=False, lazy="joined")
 
     # many to many uses association_proxy.
-    carts = association_proxy("coupon_carts", "cart", creator=lambda c: CartCoupon(cart=c))
+    carts = association_proxy(
+        "coupon_carts", "cart", creator=lambda c: CartCoupon(cart=c)
+    )
 
     # one to many.
     # returns this coupon's redemptions.
     # lazy="dynamic" returns a query object instread of an InstrumentedList.
     # this is ideal when we want to further filter the results.
-    redemptions = relationship(argument="CouponRedemption", lazy="dynamic", back_populates="coupon")
+    redemptions = relationship(
+        argument="CouponRedemption", lazy="dynamic", back_populates="coupon"
+    )
 
     def __init__(
         self,
@@ -94,10 +96,9 @@ class Coupon(RBase, Base):
         action_value,
         max_redemptions=None,
         max_redemptions_per_user=None,
-        expiration_date = None,
-        cart_qualifier = None,
+        expiration_date=None,
+        cart_qualifier=None,
     ):
-
         self.id = uuid.uuid1()
         self.shop = shop
         self.created_timestamp = now_timestamp()
@@ -124,15 +125,12 @@ class Coupon(RBase, Base):
         self.expired_timestamp = None
         if expiration_date:
             # convert date string into datetime.
-            expiration_datetime = datetime.strptime(
-                expiration_date,
-                '%Y-%m-%d'
-            )
+            expiration_datetime = datetime.strptime(expiration_date, "%Y-%m-%d")
             # convert datetime into timestamp.
             # adding 86399000 to get the end of day.
-            self.expired_timestamp = datetime_to_timestamp(
-                expiration_datetime
-            ) + 86399000
+            self.expired_timestamp = (
+                datetime_to_timestamp(expiration_datetime) + 86399000
+            )
 
     @property
     def expired_datetime(self):
@@ -160,34 +158,32 @@ class Coupon(RBase, Base):
     @property
     def human_discount(self):
         if self.action_type == "percent-off":
-            return "{}% off".format(self.action_value)
-        return "${0:.2f} off".format(
-            cents_to_dollars(self.action_value)
-        )
+            return f"{self.action_value}% off"
+        return f"${cents_to_dollars(self.action_value):.2f} off"
 
     @property
     def human_max_redemptions(self):
         if self.max_redemptions:
-            return "{}".format(self.max_redemptions)
+            return f"{self.max_redemptions}"
         return "&#8734;"
 
     @property
     def human_limit_per_customer(self):
         if self.max_redemptions_per_user:
-            return "Limit {} per customer.".format(self.max_redemptions_per_user)
+            return f"Limit {self.max_redemptions_per_user} per customer."
         return ""
 
     @property
     def human_valid_thru(self):
         if self.expired_timestamp:
             x = self.expired_datetime.strftime("%A, %b %d, %Y")
-            return "Valid thru {}.".format(x)
+            return f"Valid thru {x}."
         return ""
 
     @property
     def human_minimum_cart(self):
         if self.cart_qualifier:
-            return "any ${0:.0f} cart.".format(cents_to_dollars(self.cart_qualifier))
+            return f"any ${cents_to_dollars(self.cart_qualifier):.0f} cart."
         return "any cart."
 
     def compute_discount(self, cents):
@@ -221,7 +217,5 @@ def get_coupons_by_code(dbsession, code, shop=None):
     Remember a coupon code may not be unique across all shops.
     """
     if shop is not None:
-        return shop.coupons.filter(
-            Coupon.code == code
-        ).all()
+        return shop.coupons.filter(Coupon.code == code).all()
     return dbsession.query(Coupon).filter(Coupon.code == code).all()
diff --git a/make_post_sell/models/meta.py b/make_post_sell/models/meta.py
index 7368a9e..814c7d2 100644
--- a/make_post_sell/models/meta.py
+++ b/make_post_sell/models/meta.py
@@ -55,11 +55,11 @@ Base = declarative_base()
 
 
 COUPON_ACTION_TYPES = {
-  "dollar-off",
-  "percent-off",
+    "dollar-off",
+    "percent-off",
 }
 
-VISIBILITY_INT_TO_HUMAN ={
+VISIBILITY_INT_TO_HUMAN = {
     0: "private",
     1: "public",
     2: "unlisted",
@@ -131,7 +131,6 @@ def get_objects_by_ids(dbsession, object_ids, cls):
     object_uuids = [id_to_uuid(object_id) for object_id in object_ids]
 
     if object_uuids:
-
         # reference: https://stackoverflow.com/q/444475
         return dbsession.query(cls).filter(cls.id.in_(object_uuids)).all()
 
@@ -153,7 +152,7 @@ def now_timestamp():
 
 
 def foreign_key(class_name, column_name):
-    return ForeignKey("{}.{}".format(CLASS_TO_TABLE[class_name], column_name))
+    return ForeignKey(f"{CLASS_TO_TABLE[class_name]}.{column_name}")
 
 
 class RBase(object):
diff --git a/make_post_sell/models/product.py b/make_post_sell/models/product.py
index 706054c..7e11bcb 100644
--- a/make_post_sell/models/product.py
+++ b/make_post_sell/models/product.py
@@ -251,21 +251,21 @@ class Product(RBase, Base):
     @property
     def s3_path(self):
         """return the S3 path shop.id/product.id"""
-        return "{}/{}".format(self.shop.id, self.id)
+        return f"{self.shop.id}/{self.id}"
 
     @property
     def s3_key(self):
         """return the product S3 key"""
-        return "{}/product".format(self.s3_path)
+        return f"{self.s3_path}/product"
 
     @property
     def s3_key_preview(self):
         """return the product preview S3 key"""
-        return "{}/preview".format(self.s3_path)
+        return f"{self.s3_path}/preview"
 
     def s3_key_thumbnail(self, file_key):
         """return the thumbail S3 key"""
-        return "{}/{}".format(self.s3_path, file_key)
+        return f"{self.s3_path}/{file_key}"
 
     @property
     def s3_key_thumbnails(self):
@@ -344,15 +344,15 @@ class Product(RBase, Base):
          * an inline image (thumbnails)
          * an attachment (file download)
         """
-        file_prefix = "" if file_key == "product" else "{}-".format(file_key)
+        file_prefix = "" if file_key == "product" else f"{file_key}-"
         extension = self.extensions.get(file_key, "")
-        filename = "{}{}.{}".format(file_prefix, self.slug, extension)
-        content_disposition = "attachment; filename={}".format(filename)
+        filename = f"{file_prefix}{self.slug}.{extension}"
+        content_disposition = f"attachment; filename={filename}"
 
         if file_key in self.file_thumbnail_keys:
-            content_disposition = "inline; filename={}".format(filename)
+            content_disposition = f"inline; filename={filename}"
         elif self.is_not_sellable:
-            content_disposition = "inline; filename={}".format(filename)
+            content_disposition = f"inline; filename={filename}"
 
         return content_disposition
 
@@ -375,8 +375,8 @@ class Product(RBase, Base):
           https://my.makepostsell.com/p/product-uuid
         """
         if slug:
-            return "{}/p/{}/{}".format(request.host_url, self.id, self.slug)
-        return "{}/p/{}".format(request.host_url, self.id)
+            return f"{request.host_url}/p/{self.id}/{self.slug}"
+        return f"{request.host_url}/p/{self.id}"
 
     def absolute_edit_url(self, request):
         """
@@ -387,7 +387,7 @@ class Product(RBase, Base):
           https://makepostsell.com/p/product-uuid/edit
         """
 
-        return "{}/edit".format(self.absolute_url(request, slug=False))
+        return f"{self.absolute_url(request, slug=False)}/edit"
 
     @property
     def shop_uuid_str(self):
@@ -518,7 +518,7 @@ def get_products_by_keywords(dbsession, keywords, shop=None):
         product_query = dbsession.query(Product)
 
     for keyword in keywords:
-        keyword_filter = Product.title.ilike("%{}%".format(keyword))
+        keyword_filter = Product.title.ilike(f"%{keyword}%")
         # the product _must_ be public (1).
         products = (
             product_query.filter(keyword_filter).filter(Product.visibility == 1).all()
diff --git a/make_post_sell/models/shop.py b/make_post_sell/models/shop.py
index 856f28b..8a2ce9a 100644
--- a/make_post_sell/models/shop.py
+++ b/make_post_sell/models/shop.py
@@ -1,10 +1,18 @@
 import uuid
 
 from sqlalchemy import Column, BigInteger, Boolean, Unicode, UnicodeText, func
-        
+
 from sqlalchemy import and_
 
-from .meta import Base, RBase, UUIDType, now_timestamp, foreign_key, get_object_by_id, get_objects_by_ids
+from .meta import (
+    Base,
+    RBase,
+    UUIDType,
+    now_timestamp,
+    foreign_key,
+    get_object_by_id,
+    get_objects_by_ids,
+)
 
 from sqlalchemy.ext.associationproxy import association_proxy
 
@@ -62,8 +70,8 @@ class Shop(RBase, Base):
 
     # these keys allow make_post_sell to charge
     # cards on behalf of the shop's stripe account.
-    #stripe_secret_api_key = Column(Unicode(64), nullable=True)
-    #stripe_public_api_key = Column(Unicode(64), nullable=True)
+    # stripe_secret_api_key = Column(Unicode(64), nullable=True)
+    # stripe_public_api_key = Column(Unicode(64), nullable=True)
     stripe_secret_api_key = Column(Unicode(128), nullable=True)
     stripe_public_api_key = Column(Unicode(128), nullable=True)
 
@@ -101,7 +109,9 @@ class Shop(RBase, Base):
 
     # lazy='dynamic' returns a query object instead of collection.
     # Reference: http://docs.sqlalchemy.org/en/latest/orm/collections.html
-    shop_locations = relationship(argument="ShopLocation", lazy="dynamic", back_populates="shop")
+    shop_locations = relationship(
+        argument="ShopLocation", lazy="dynamic", back_populates="shop"
+    )
 
     # lazy='dynamic' returns a query object instead of collection.
     # Reference: http://docs.sqlalchemy.org/en/latest/orm/collections.html
@@ -121,10 +131,14 @@ class Shop(RBase, Base):
     def get_usershop_for_user(self, user):
         """Given a User object, return the UserShop object or None."""
         if self.dbsession is not None:
-            return self.dbsession.query(UserShop).filter(
-                UserShop.shop == self,
-                UserShop.user == user,
-            ).one_or_none()
+            return (
+                self.dbsession.query(UserShop)
+                .filter(
+                    UserShop.shop == self,
+                    UserShop.user == user,
+                )
+                .one_or_none()
+            )
 
     def add_user_to_shop(self, user, role_id=0):
         """Add User object to UserShop."""
@@ -172,6 +186,7 @@ class Shop(RBase, Base):
         if hasattr(self, "_stripe") == False:
             if self.stripe_secret_api_key:
                 import stripe
+
                 stripe.api_key = self.stripe_secret_api_key
                 self._stripe = stripe
             else:
@@ -180,15 +195,19 @@ class Shop(RBase, Base):
 
     def stripe_user_shop(self, user):
         """Return the stripe_user_shop object from our database for this user, or None."""
-        return self.dbsession.query(StripeUserShop).filter(
-            StripeUserShop.user == user,
-            StripeUserShop.shop == self,
-        ).one_or_none()
+        return (
+            self.dbsession.query(StripeUserShop)
+            .filter(
+                StripeUserShop.user == user,
+                StripeUserShop.shop == self,
+            )
+            .one_or_none()
+        )
 
     def stripe_customer_id(self, user):
         """Return the stripe_customer id from our database for this user, or None."""
         stripe_user_shop = self.stripe_user_shop(user)
-        
+
         if stripe_user_shop:
             return stripe_user_shop.cus_id
 
@@ -201,7 +220,6 @@ class Shop(RBase, Base):
         stripe_customer_id = self.stripe_customer_id(user)
 
         if stripe_customer_id is None:
-
             if create == False:
                 return None
 
@@ -236,7 +254,7 @@ class Shop(RBase, Base):
 
     @property
     def theme_link_color(self):
-        return color_scale(self.theme_base_color, .75)
+        return color_scale(self.theme_base_color, 0.75)
 
     def absolute_url(self, request, slug=True):
         """
@@ -247,8 +265,8 @@ class Shop(RBase, Base):
           https://my.makepostsell.com/s/<shop-uuid>
         """
         if slug:
-            return "{}/s/{}/{}".format(request.host_url, self.id, self.slug)
-        return "{}/s/{}".format(request.host_url, self.id)
+            return f"{request.host_url}/s/{self.id}/{self.slug}"
+        return f"{request.host_url}/s/{self.id}"
 
     def absolute_settings_url(self, request):
         """
@@ -258,7 +276,7 @@ class Shop(RBase, Base):
 
           https://my.makepostsell.com/s/<shop-uuid>/settings
         """
-        return "{}/settings".format(self.absolute_url(request, slug=False))
+        return f"{self.absolute_url(request, slug=False)}/settings"
 
     def absolute_about_url(self, request):
         """
@@ -269,16 +287,16 @@ class Shop(RBase, Base):
           https://my.makepostsell.com/s/<shop-uuid>/about
         """
         # why ure slug for this URL, is it for SEO?
-        return "{}/about".format(self.absolute_url(request))
+        return f"{self.absolute_url(request)}/about"
 
     def absolute_terms_url(self, request):
-        return "{}/terms".format(self.absolute_url(request, slug=False))
-    
+        return f"{self.absolute_url(request, slug=False)}/terms"
+
     def absolute_privacy_policy_url(self, request):
-        return "{}/privacy-policy".format(self.absolute_url(request, slug=False))
+        return f"{self.absolute_url(request, slug=False)}/privacy-policy"
 
     def absolute_sales_url(self, request):
-        return "{}/sales".format(self.absolute_url(request, slug=False))
+        return f"{self.absolute_url(request, slug=False)}/sales"
 
     def set_description(self, new_description):
         self.description = new_description
@@ -303,8 +321,9 @@ class Shop(RBase, Base):
         self.terms_of_service_html = markdown_to_html(self.terms_of_service_raw, self)
 
     def get_carts_for_user(self, user):
-        """return all of this Shop's Cart objects for the given User."""    
+        """return all of this Shop's Cart objects for the given User."""
         from .cart import Cart
+
         return self.carts.filter(and_(Cart.shop == self, Cart.user == user))
 
     def make_cart_active_for_user(self, user, cart):
@@ -324,6 +343,7 @@ class Shop(RBase, Base):
 
     def create_new_cart_for_user(self, user):
         from .cart import Cart
+
         cart = Cart()
         cart.user = user
         cart.shop = self
@@ -382,7 +402,7 @@ def get_shop_by_id(dbsession, shop_id):
     """Try to get Shop object by id or return None."""
     return get_object_by_id(dbsession, shop_id, Shop)
 
+
 def get_shops_by_ids(dbsession, shop_ids):
     """Try to get Shop objects by ids or return None."""
     return get_objects_by_ids(dbsession, shop_ids, Shop)
-
diff --git a/make_post_sell/models/user.py b/make_post_sell/models/user.py
index 84d5e40..cdf57c4 100644
--- a/make_post_sell/models/user.py
+++ b/make_post_sell/models/user.py
@@ -38,6 +38,7 @@ except:
 def generate_password(size=32):
     """Return a system generated password"""
     from random import choice
+
     letters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
     digits = "0123456789"
     pool = letters + digits
@@ -56,7 +57,7 @@ class User(RBase, Base):
     name = Column(Unicode(64), unique=True, nullable=False)
     full_name = Column(Unicode(64))
     email = Column(Unicode(64), unique=True, nullable=False)
-    #email_unverified = Column(Unicode(64))
+    # email_unverified = Column(Unicode(64))
     password = Column(Unicode(64))
     password_attempts = Column(Integer, default=0)
     password_timestamp = Column(BigInteger)
@@ -81,7 +82,9 @@ class User(RBase, Base):
     shops = association_proxy("user_shops", "shop", creator=lambda s: UserShop(shop=s))
 
     # many to many uses association_proxy.
-    stripe_shops = association_proxy("stripe_shops", "shop", creator=lambda s: StripeUserShop(shop=s))
+    stripe_shops = association_proxy(
+        "stripe_shops", "shop", creator=lambda s: StripeUserShop(shop=s)
+    )
 
     # many to many uses association_proxy.
     # returns all the products that a user has purchased.
@@ -101,15 +104,16 @@ class User(RBase, Base):
     # this is ideal when we want to further filter the results.
     carts = relationship(argument="Cart", lazy="dynamic", back_populates="user")
 
-    addresses = relationship(argument="UserAddress", lazy="dynamic", back_populates="user")
+    addresses = relationship(
+        argument="UserAddress", lazy="dynamic", back_populates="user"
+    )
 
     def __init__(self, email):
-        self.name = unicode("user-{}".format(generate_password(size=8)))
+        self.name = unicode(f"user-{generate_password(size=8)}")
         self.created_timestamp = now_timestamp()
         self.id = uuid.uuid1()
         self.email = unicode(email)
 
-
         # TODO: remove this column.
         self.active_cart_id = uuid.uuid1()
 
@@ -119,10 +123,11 @@ class User(RBase, Base):
 
     def _generate_raw_password(self):
         """Return a system generated password"""
-        #return generate_password(size)
+        # return generate_password(size)
         from random import choice
-        numbers = '0123456789'
-        return "".join([choice(numbers) for i in range(0,6)])
+
+        numbers = "0123456789"
+        return "".join([choice(numbers) for i in range(0, 6)])
 
     def new_password(self):
         """Generate and return raw password, store password hash into DB."""
@@ -130,8 +135,7 @@ class User(RBase, Base):
 
         # bcrypt works with bytes so we encode to utf-8.
         self.password = bcrypt.hashpw(
-            raw_password.encode("utf-8"),
-            bcrypt.gensalt()
+            raw_password.encode("utf-8"), bcrypt.gensalt()
         ).decode("utf-8")
         self.password_timestamp = now_timestamp()
         self.password_attempts = 0
@@ -159,7 +163,7 @@ class User(RBase, Base):
             stored_hash.encode("utf-8"),
         ).decode("utf-8")
 
-        log.info("new_hash={} stored_hash={}".format(new_hash, stored_hash))
+        log.info(f"new_hash={new_hash} stored_hash={stored_hash}")
 
         if new_hash == stored_hash:
             return True
@@ -184,9 +188,11 @@ class User(RBase, Base):
     def active_shop(self):
         """Return the user's active shop, or None."""
         if self.active_shop_id:
-            return self.dbsession.query(Shop).filter(
-                Shop.id == self.active_shop_id
-            ).one_or_none()
+            return (
+                self.dbsession.query(Shop)
+                .filter(Shop.id == self.active_shop_id)
+                .one_or_none()
+            )
 
         elif self.shops:
             # if a user doesn't have an active shop but it has
@@ -244,7 +250,7 @@ class User(RBase, Base):
         for address in self.addresses:
             if address.id == self.active_address_id:
                 return address
-        
+
 
 def _user_by_name_query(dbsession, name):
     """query User by case insensitive name."""
diff --git a/make_post_sell/tests/test_functional.py b/make_post_sell/tests/test_functional.py
index c3eaa9a..74e2a44 100644
--- a/make_post_sell/tests/test_functional.py
+++ b/make_post_sell/tests/test_functional.py
@@ -83,16 +83,17 @@ class UnauthenticatedFunctionalTests(FunctionalTests):
 
     @patch("smtplib.SMTP")
     def test_user_log_in(self, mock_smtp):
-        redirect_res1 = self.testapp.post("/join-or-log-in", {"email": "test@example.com"})
+        redirect_res1 = self.testapp.post(
+            "/join-or-log-in", {"email": "test@example.com"}
+        )
         self.assertIn(
             b"Check email for a 6 digit verification code to log in. test@example.com",
-            redirect_res1.follow().body)
+            redirect_res1.follow().body,
+        )
 
 
 class AuthenticatedFunctionalTests(FunctionalTests):
-
     def setUp(self):
-
         super(AuthenticatedFunctionalTests, self).setUp()
 
         self.shop1_params = {
@@ -134,25 +135,21 @@ class AuthenticatedFunctionalTests(FunctionalTests):
         }
 
         # create test user1 and user2.
-        self.user1 = get_or_create_user_by_email(
-            self.dbsession, "test1@example.com"
-        )
-        self.user2 = get_or_create_user_by_email(
-            self.dbsession, "test2@example.com"
-        )
+        self.user1 = get_or_create_user_by_email(self.dbsession, "test1@example.com")
+        self.user2 = get_or_create_user_by_email(self.dbsession, "test2@example.com")
 
         # capture user credentials needed for authentication.
         self.user1_creds = (
             "test1@example.com",
             # returns the raw auto-generated password used
             # in one-time-password links OTP
-            self.user1.new_password()
+            self.user1.new_password(),
         )
         self.user2_creds = (
             "test2@example.com",
             # returns the raw auto-generated password used
             # in one-time-password links OTP
-            self.user2.new_password()
+            self.user2.new_password(),
         )
 
         # flush new users to database.
@@ -164,12 +161,8 @@ class AuthenticatedFunctionalTests(FunctionalTests):
         transaction.manager.commit()
 
         # requery User objects to avoid detached instance error.
-        self.user1 = get_or_create_user_by_email(
-            self.dbsession, "test1@example.com"
-        )
-        self.user2 = get_or_create_user_by_email(
-            self.dbsession, "test2@example.com"
-        )
+        self.user1 = get_or_create_user_by_email(self.dbsession, "test1@example.com")
+        self.user2 = get_or_create_user_by_email(self.dbsession, "test2@example.com")
 
     def _clean_up_user(self, user):
         # print("deleteing user {} from dbsession.".format(user.name))
@@ -199,7 +192,6 @@ class AuthenticatedFunctionalTests(FunctionalTests):
         # transaction.manager.commit()
         super(AuthenticatedFunctionalTests, self).tearDown()
 
-
     def log_in_user(self, user_creds):
         # log in user.
         res_login = self.testapp.post(
@@ -217,7 +209,7 @@ class AuthenticatedFunctionalTests(FunctionalTests):
         valid_creds = self.user1_creds
         invalid_creds = (self.user1_creds[0], "invalid")
 
-        for i in range(0,12):
+        for i in range(0, 12):
             self.log_in_user(invalid_creds)
 
         self.log_in_user(valid_creds)
@@ -260,8 +252,9 @@ class AuthenticatedFunctionalTests(FunctionalTests):
         res = redirect_res.follow()
         self.assertIn(b"You must have a shop editor role to access that.", res.body)
 
-    def test_create_new_shop(self, user_creds=None, shop_params=None, log_out_user=False):
-
+    def test_create_new_shop(
+        self, user_creds=None, shop_params=None, log_out_user=False
+    ):
         if user_creds is None:
             user_creds = self.user1_creds
 
@@ -287,7 +280,7 @@ class AuthenticatedFunctionalTests(FunctionalTests):
         self.assertTrue(shop.is_not_ready)
 
         # add stripe keys to the newly created shop to make it ready.
-        res = self.testapp.post("/s/{}/settings".format(shop.id), shop_params)
+        res = self.testapp.post(f"/s/{shop.id}/settings", shop_params)
         res_body = res.body.decode()
         self.assertIn(
             "You set the shop's stripe_public_api_key.",
@@ -337,23 +330,23 @@ class AuthenticatedFunctionalTests(FunctionalTests):
         )
 
     def test_new_product_missing_required_fields(self):
-
         # log in and create a new shop.
         shop = self.test_create_new_shop(
             user_creds=self.user1_creds,
             shop_params=self.shop1_params,
-            log_out_user=False
+            log_out_user=False,
         )
 
         product_params = self.product1_params
         del product_params["description"]
-        #redirect_res1 = self.testapp.post("/p/new", product_params)
-        #res = redirect_res1.follow()
-        res = self.testapp.post("/p/new?shop_id={}".format(shop.id), product_params)
+        # redirect_res1 = self.testapp.post("/p/new", product_params)
+        # res = redirect_res1.follow()
+        res = self.testapp.post(f"/p/new?shop_id={shop.id}", product_params)
         self.assertIn("You must fill out all fields.", res.body.decode())
 
-    def test_new_product(self, user_creds=None, shop_params=None, product_params=None, log_out_user=False):
-
+    def test_new_product(
+        self, user_creds=None, shop_params=None, product_params=None, log_out_user=False
+    ):
         if user_creds is None:
             user_creds = self.user1_creds
 
@@ -369,7 +362,7 @@ class AuthenticatedFunctionalTests(FunctionalTests):
             shop_params=shop_params,
         )
 
-        redirect_res = self.testapp.post("/p/new?shop_id={}".format(shop.id), product_params)
+        redirect_res = self.testapp.post(f"/p/new?shop_id={shop.id}", product_params)
         res = redirect_res.follow()
         self.assertIn("Great, next you may upload files.", res.body.decode())
 
@@ -377,7 +370,6 @@ class AuthenticatedFunctionalTests(FunctionalTests):
             self.testapp.get("/log-out")
 
     def test_new_product_when_user_does_not_have_editor_role_on_shop(self):
-
         # log in user1.
         self.log_in_user(self.user1_creds)
 
@@ -396,9 +388,11 @@ class AuthenticatedFunctionalTests(FunctionalTests):
 
         # make user2 create a new product on a shop she doesn't own.
         params = self.product1_params
-        redirect_res = self.testapp.post("/p/new?shop_id={}".format(shop_id), params)
+        redirect_res = self.testapp.post(f"/p/new?shop_id={shop_id}", params)
         res = redirect_res.follow()
-        self.assertIn("You must have a shop editor role to access that.", res.body.decode())
+        self.assertIn(
+            "You must have a shop editor role to access that.", res.body.decode()
+        )
 
     def test_new_product_price_history(self):
         self.test_new_product(
@@ -416,12 +410,10 @@ class AuthenticatedFunctionalTests(FunctionalTests):
         self.assertEqual(product.price_history.count(), 1)
         self.assertEqual(product.price_in_cents, 350)
 
-
     # this patch requires an argument added to test method `mock_smtp`.
     @patch("smtplib.SMTP")
     @patch("make_post_sell.models.Product.is_ready", mock_always_true)
     def test_cart_checkout_for_shop(self, mock_smtp):
-
         # 1. log in as user1.
         # 2. create new shop.
         # 3. make new shop ready for checkout.
@@ -446,12 +438,14 @@ class AuthenticatedFunctionalTests(FunctionalTests):
         self.log_in_user(self.user2_creds)
 
         # add product to cart.
-        redirect_res1 = self.testapp.get("/cart/add?product_id={}&shop_id={}".format(product.id, shop.id))
+        redirect_res1 = self.testapp.get(
+            f"/cart/add?product_id={product.id}&shop_id={shop.id}"
+        )
         redirect_res2 = redirect_res1.follow()
         res = redirect_res2.follow()
         res_body = res.body.decode()
 
-        self.assertIn("You added \"russell\'s product\" to your cart.", res_body)
+        self.assertIn('You added "russell\'s product" to your cart.', res_body)
 
         carts = get_all_carts(self.dbsession)
 
@@ -472,10 +466,7 @@ class AuthenticatedFunctionalTests(FunctionalTests):
         self.assertEqual(1, user_2_cart.count)
 
         redirect_res = self.testapp.get(
-            "/u/cart/{}/checkout?shop_id={}".format(
-                user_2_cart.id,
-                shop.id
-            )
+            f"/u/cart/{user_2_cart.id}/checkout?shop_id={shop.id}"
         )
         redirect_res2 = redirect_res1.follow()
         res = redirect_res2.follow()
@@ -529,7 +520,6 @@ class AuthenticatedFunctionalTests(FunctionalTests):
 
     @patch("make_post_sell.models.Product.is_ready", mock_always_true)
     def make_new_coupon_for_shop(self, coupon_params=None):
-
         # 1. log in as user1.
         # 2. create new shop.
         # 3. make new shop ready for checkout.
@@ -553,7 +543,7 @@ class AuthenticatedFunctionalTests(FunctionalTests):
 
         # create a new shop coupon.
         res = self.testapp.post(
-            "/s/{}/coupon/new".format(shop.id),
+            f"/s/{shop.id}/coupon/new",
             coupon_params,
         )
         return res
@@ -572,7 +562,7 @@ class AuthenticatedFunctionalTests(FunctionalTests):
     # this patch requires an argument added to test method `mock_smtp`.
     @patch("smtplib.SMTP")
     @patch("make_post_sell.models.Product.is_ready", mock_always_true)
-    def test_checkout_with_coupon_code(self,  mock_smtp):
+    def test_checkout_with_coupon_code(self, mock_smtp):
         res = self.make_new_coupon_for_shop()
         res = res.follow()
         self.assertIn("You created a new coupon!", res.body.decode())
@@ -585,20 +575,15 @@ class AuthenticatedFunctionalTests(FunctionalTests):
 
         # query the new shop from database.
         shop = get_shop_by_name(self.dbsession, self.shop1_params["name"])
- 
+
         coupons = get_coupons_by_code(self.dbsession, self.coupon1_params["code"])
         coupon = coupons[0]
 
         # apply coupon to user2's active cart.
-        self.testapp.post(
-            "/coupon/apply?&coupon_id={}&shop_id={}".format(
-                coupon.id,
-                shop.id,
-            )
-        )
+        self.testapp.post(f"/coupon/apply?&coupon_id={coupon.id}&shop_id={shop.id}")
 
         # verify coupon was applied.
-        res_redirect1 = self.testapp.get("/cart?shop_id={}".format(shop.id))
+        res_redirect1 = self.testapp.get(f"/cart?shop_id={shop.id}")
         res = res_redirect1.follow()
         res_body = res.body.decode()
         self.assertIn("Slippery Halloween Party", res_body)
@@ -610,7 +595,7 @@ class AuthenticatedFunctionalTests(FunctionalTests):
         product = all_products.one()
 
         # add product to user2's active cart.
-        self.testapp.get("/cart/add?product_id={}&shop_id={}".format(product.uuid_str, shop.id))
+        self.testapp.get(f"/cart/add?product_id={product.uuid_str}&shop_id={shop.id}")
 
         # the stripe migration to SetupIntents broke this end-to-end test routine.
         """
diff --git a/make_post_sell/views/authentication.py b/make_post_sell/views/authentication.py
index 54f09d0..742309c 100644
--- a/make_post_sell/views/authentication.py
+++ b/make_post_sell/views/authentication.py
@@ -58,9 +58,7 @@ def join_or_log_in(request):
 
         if user.throttle_password():
             msg = (
-                "Check email for a 6 digit verification code to log in. {}".format(
-                    user.email
-                ),
+                f"Check email for a 6 digit verification code to log in. {user.email}",
                 "info",
             )
 
@@ -74,9 +72,7 @@ def join_or_log_in(request):
             send_verification_digits_to_email(request, user.email, raw_otp)
 
             msg = (
-                "Check email for a 6 digit verification code to log in. {}".format(
-                    user.email
-                ),
+                f"Check email for a 6 digit verification code to log in. {user.email}",
                 "info",
             )
 
@@ -85,7 +81,7 @@ def join_or_log_in(request):
         email_encoded = urlencode(
             {"email": email, "next": request.params.get("next", "")}
         )
-        return HTTPFound("/verification-challenge?{}".format(email_encoded))
+        return HTTPFound(f"/verification-challenge?{email_encoded}")
 
     return {
         "title": "join or log in",
@@ -113,7 +109,7 @@ def verification_challenge(request):
             name = ""
             if user.full_name:
                 name = user.name
-            msg = ("Welcome {}".format(name), "success")
+            msg = (f"Welcome {name}", "success")
             request.session["authenticated_user_id"] = str(user.id)
             request.session.flash(msg)
 
diff --git a/make_post_sell/views/cart.py b/make_post_sell/views/cart.py
index d7202f2..a0c0809 100644
--- a/make_post_sell/views/cart.py
+++ b/make_post_sell/views/cart.py
@@ -128,7 +128,7 @@ def cart_activate(request):
             request.dbsession.add(new_cart)
             request.session.flash(msg)
             request.session["active_cart_id"] = new_cart.uuid_str
-            return HTTPFound("/cart/{}".format(new_cart.id))
+            return HTTPFound(f"/cart/{new_cart.id}")
 
     request.session.flash(msg)
     return HTTPFound(get_referer_or_home(request))
@@ -162,7 +162,7 @@ def cart_delete(request):
 @view_config(route_name="cart")
 def cart(request):
     """Load active cart from session. Create cart if not in session."""
-    return HTTPFound("/cart/{}".format(request.active_cart.id))
+    return HTTPFound(f"/cart/{request.active_cart.id}")
 
 
 @view_config(route_name="cart_by_id", renderer="cart.j2")
@@ -186,7 +186,7 @@ def cart_by_id(request):
                 request.dbsession.add(cart)
                 request.dbsession.flush()
                 msg = (
-                    "Invalid coupon ({}) removed from cart.".format(coupon.code),
+                    f"Invalid coupon ({coupon.code}) removed from cart.",
                     "info",
                 )
                 request.session.flash(msg)
@@ -234,7 +234,7 @@ def cart_add_product(request):
         msg = ("that content is not for sale or purchase.", "error")
 
     else:
-        msg = ('You added "{}" to your cart.'.format(product.title), "success")
+        msg = (f'You added "{product.title}" to your cart.', "success")
         request.active_cart.add_product(product)
         request.dbsession.add(request.active_cart)
         request.dbsession.flush()
@@ -273,7 +273,7 @@ def cart_remove_product(request):
         msg = ("That product_id does not exist.", "error")
 
     else:
-        msg = ('You removed "{}" from the cart.'.format(product.title), "success")
+        msg = (f'You removed "{product.title}" from the cart.', "success")
         cart.remove_product(product)
         cart.remove_handling_if_no_physical_products()
         request.dbsession.add(cart)
@@ -335,7 +335,7 @@ def cart_quantity_product(request):
         return HTTPFound("/cart")
     else:
         msg = (
-            'You updated the quantity of "{}" in the cart.'.format(product.title),
+            f'You updated the quantity of "{product.title}" in the cart.',
             "success",
         )
         cart.set_product_quantity(product, quantity)
@@ -390,7 +390,7 @@ def cart_checkout(request):
     stripe_user_shop = request.shop.stripe_user_shop(request.user)
 
     if "cart_id" not in request.matchdict:
-        return HTTPFound("/u/cart/{}/checkout".format(request.active_cart.id))
+        return HTTPFound(f"/u/cart/{request.active_cart.id}/checkout")
 
     cart = get_cart_from_matchdict(request)
 
@@ -420,12 +420,18 @@ def cart_checkout(request):
                 return HTTPFound(get_referer_or_home(request))
 
             if not cart.handling_option:
-                msg = ("Please select a handling option for your physical items.", "error")
+                msg = (
+                    "Please select a handling option for your physical items.",
+                    "error",
+                )
                 request.session.flash(msg)
                 return HTTPFound(get_referer_or_home(request))
 
             if not request.user.active_address:
-                msg = ("Please add a shipping address to proceed with checkout.", "info")
+                msg = (
+                    "Please add a shipping address to proceed with checkout.",
+                    "info",
+                )
                 request.session.flash(msg)
                 return HTTPFound("/u/addresses")
 
diff --git a/make_post_sell/views/content.py b/make_post_sell/views/content.py
index 22bd62e..495dd19 100644
--- a/make_post_sell/views/content.py
+++ b/make_post_sell/views/content.py
@@ -21,10 +21,10 @@ def content(request):
             return HTTPFound(get_referer_or_home(request))
 
     if product.is_sellable:
-        return HTTPFound("/p/{}/{}".format(product.id, product.slug))
+        return HTTPFound(f"/p/{product.id}/{product.slug}")
 
     if "slug" not in request.matchdict:
-        return HTTPFound("/c/{}/{}".format(product.id, product.slug))
+        return HTTPFound(f"/c/{product.id}/{product.slug}")
 
     signed_get_object_url = None
 
diff --git a/make_post_sell/views/coupon.py b/make_post_sell/views/coupon.py
index 47dbf69..f15c6fd 100644
--- a/make_post_sell/views/coupon.py
+++ b/make_post_sell/views/coupon.py
@@ -68,7 +68,7 @@ def coupon_new(request):
             )
             request.dbsession.add(coupon)
             request.dbsession.flush()
-            return HTTPFound("/s/{}/coupons".format(request.shop.id))
+            return HTTPFound(f"/s/{request.shop.id}/coupons")
 
     return request.params
 
@@ -82,7 +82,7 @@ def coupon_apply_to_cart(request):
     if coupon is None:
         msg = ("That coupon_id does not exist.", "error")
         request.session.flash(msg)
-        return HTTPFound("/cart/{}".format(request.active_cart.id))
+        return HTTPFound(f"/cart/{request.active_cart.id}")
 
     if coupon not in request.active_cart.coupons:
         msg = ("The coupon was applied to your cart.", "success")
@@ -93,7 +93,7 @@ def coupon_apply_to_cart(request):
         msg = ("The coupon was already applied to your cart.", "success")
 
     request.session.flash(msg)
-    return HTTPFound("/cart/{}".format(request.active_cart.id))
+    return HTTPFound(f"/cart/{request.active_cart.id}")
 
 
 @view_config(route_name="coupon_remove_from_cart", request_method="POST")
@@ -125,7 +125,7 @@ def coupon_remove_from_cart(request):
         else:
             msg = ("The coupon was already removed from your cart.", "success")
         request.session.flash(msg)
-        return HTTPFound("/cart/{}".format(cart_id))
+        return HTTPFound(f"/cart/{cart_id}")
 
     request.session.flash(msg)
     return HTTPFound(get_referer_or_home(request))
diff --git a/make_post_sell/views/product.py b/make_post_sell/views/product.py
index 3f2b2b6..0c383b8 100644
--- a/make_post_sell/views/product.py
+++ b/make_post_sell/views/product.py
@@ -35,10 +35,10 @@ def product(request):
             return HTTPFound(get_referer_or_home(request))
 
     if product.is_not_sellable:
-        return HTTPFound("/c/{}/{}".format(product.id, product.slug))
+        return HTTPFound(f"/c/{product.id}/{product.slug}")
 
     if "slug" not in request.matchdict:
-        return HTTPFound("/p/{}/{}".format(product.id, product.slug))
+        return HTTPFound(f"/p/{product.id}/{product.slug}")
 
     signed_get_object_url = None
 
@@ -134,7 +134,7 @@ def product_new(request):
                 request.dbsession.flush()
                 msg = ("Great, next you may upload files.", "success")
                 request.session.flash(msg)
-                return HTTPFound("/p/{}/edit".format(product.id))
+                return HTTPFound(f"/p/{product.id}/edit")
 
     elif title or description or price:
         msg = ("You must fill out all fields.", "error")
@@ -172,12 +172,10 @@ def product_edit_description(request):
         request.dbsession.flush()
 
     return {
-        "markup_subject": "Product Description for {}".format(product.title),
+        "markup_subject": f"Product Description for {product.title}",
         "markup_rendered": product.description_html,
         "markup_raw": product.description,
-        "markup_form_path": "{}/description".format(
-            product.absolute_url(request, slug=False)
-        ),
+        "markup_form_path": f"{product.absolute_url(request, slug=False)}/description",
     }
 
 
@@ -266,7 +264,7 @@ def product_edit(request):
             ContentDisposition=product.get_content_disposition(file_key),
             ContentType=product.get_content_type(file_key),
             CacheControl=cache_control,
-            Key="{}/{}".format(product.s3_path, file_key),
+            Key=f"{product.s3_path}/{file_key}",
             MetadataDirective="REPLACE",
         )
 
@@ -279,7 +277,7 @@ def product_edit(request):
         # get file size & store in our database.
         response = request.secure_uploads_client.head_object(
             Bucket=request.app["bucket.secure_uploads"],
-            Key="{}/{}".format(product.s3_path, file_key),
+            Key=f"{product.s3_path}/{file_key}",
         )
 
         product_content_length = response["ContentLength"]
@@ -294,9 +292,7 @@ def product_edit(request):
 
         # redirect back to this page to clear
         # the params posted by the s3 webhooks.
-        return HTTPFound(
-            "/p/{}/{}/edit?uploaded={}".format(product.id, product.slug, file_key)
-        )
+        return HTTPFound(f"/p/{product.id}/{product.slug}/edit?uploaded={file_key}")
 
     if product_modified and product.error_message is None:
         request.dbsession.add(product)
@@ -305,7 +301,7 @@ def product_edit(request):
     signed_posts = {}
 
     for file_key in product.file_keys:
-        key_starts_with = "{}/{}.".format(product.s3_path, file_key)
+        key_starts_with = f"{product.s3_path}/{file_key}."
         conditions = [
             {"success_action_redirect": product.absolute_edit_url(request)},
             ["starts-with", "$key", key_starts_with],
@@ -374,18 +370,29 @@ def product_inventory_edit(request):
         if quantity is not None:
             try:
                 quantity = int(quantity)
-                inventory = next((inv for inv in product.inventories if inv.shop_location_id == location.id), None)
+                inventory = next(
+                    (
+                        inv
+                        for inv in product.inventories
+                        if inv.shop_location_id == location.id
+                    ),
+                    None,
+                )
                 if inventory:
                     if inventory.quantity != quantity:
                         inventory.update_quantity(quantity)
                         request.dbsession.add(inventory)
                         updated = True
                 else:
-                    inventory = Inventory(shop_location=location, product=product, quantity=quantity)
+                    inventory = Inventory(
+                        shop_location=location, product=product, quantity=quantity
+                    )
                     request.dbsession.add(inventory)
                     updated = True
             except ValueError:
-                request.session.flash((f"Invalid quantity for location {location.name}.", "error"))
+                request.session.flash(
+                    (f"Invalid quantity for location {location.name}.", "error")
+                )
 
     if updated:
         request.dbsession.flush()
diff --git a/make_post_sell/views/shop.py b/make_post_sell/views/shop.py
index dddb805..75d6b60 100644
--- a/make_post_sell/views/shop.py
+++ b/make_post_sell/views/shop.py
@@ -76,7 +76,7 @@ def home(request):
 def shop(request):
     shop = get_shop_from_matchdict(request)
     if "slug" not in request.matchdict:
-        return HTTPFound("/s/{}/{}".format(shop.id, shop.slug))
+        return HTTPFound(f"/s/{shop.id}/{shop.slug}")
 
     return {
         "products": get_products_from_a_shop(shop),
@@ -106,7 +106,7 @@ def shop_products(request):
 def shop_about(request):
     shop = get_shop_from_matchdict(request)
     if "slug" not in request.matchdict:
-        return HTTPFound("/s/{}/{}/about".format(shop.id, shop.slug))
+        return HTTPFound(f"/s/{shop.id}/{shop.slug}/about")
     return {}
 
 
@@ -177,7 +177,7 @@ def shop_new(request):
                 "success",
             )
             request.session.flash(msg)
-            return HTTPFound("/s/{}/settings".format(shop.id))
+            return HTTPFound(f"/s/{shop.id}/settings")
 
     elif name or description or billing_address or phone_number:
         msg = ("You must fill out all fields.", "error")
@@ -301,7 +301,7 @@ def shop_users(request):
         # send an invitation email to the new user.
         send_invite_email(request, email_to_invite, request.user, request.shop)
 
-        msg = ("You invited {} to the shop.".format(email_to_invite), "success")
+        msg = (f"You invited {email_to_invite} to the shop.", "success")
         request.session.flash(msg)
 
     return {
@@ -327,9 +327,9 @@ def shop_user_remove(request):
             else:
                 user_shop = request.shop.get_usershop_for_user(user)
                 request.dbsession.delete(user_shop)
-                msg = ("You removed {} from the shop.".format(user.email), "success")
+                msg = (f"You removed {user.email} from the shop.", "success")
                 request.session.flash(msg)
-    return HTTPFound("/s/{}/users".format(request.shop.id))
+    return HTTPFound(f"/s/{request.shop.id}/users")
 
 
 @view_config(route_name="shop_settings", renderer="shop_settings.j2")
@@ -376,7 +376,7 @@ def shop_settings(request):
     if uploaded_file_key:
         request.session.flash(
             (
-                "You successfully uploaded a new {} file!".format(uploaded_file_key),
+                f"You successfully uploaded a new {uploaded_file_key} file!",
                 "success",
             )
         )
@@ -478,7 +478,7 @@ def shop_settings(request):
             shop.maint_mode = maint_mode
             request.session.flash(
                 (
-                    "You turned {} maint_mode".format(maint_mode_checkbox),
+                    f"You turned {maint_mode_checkbox} maint_mode",
                     "success",
                 )
             )
@@ -508,10 +508,10 @@ def shop_settings(request):
                 "Bucket": s3_webhook_bucket,
                 "Key": s3_webhook_key,
             },
-            ContentDisposition="inline; filename={}".format(file_key),
+            ContentDisposition=f"inline; filename={file_key}",
             ContentType=content_type,
             CacheControl=cache_control,
-            Key="{}/meta/{}".format(shop.id, file_key),
+            Key=f"{shop.id}/meta/{file_key}",
             MetadataDirective="REPLACE",
         )
 
@@ -531,7 +531,7 @@ def shop_settings(request):
 
         # redirect back to this page to clear
         # the params posted by the s3 webhooks.
-        return HTTPFound("/s/{}/settings?uploaded={}".format(shop.id, file_key))
+        return HTTPFound(f"/s/{shop.id}/settings?uploaded={file_key}")
 
     signed_posts = {}
     get_endpoints = {}
@@ -541,7 +541,7 @@ def shop_settings(request):
         # object path start's with the shop's s3 namespace (uuid) and only for
         # particular file keys. This prevents a user from writing files into
         # a shops namespace which is owned by a different user.
-        key_starts_with = "{}/meta/{}.{}".format(shop.id, file_key, "$filename")
+        key_starts_with = f"{shop.id}/meta/{file_key}.$filename"
         conditions = [
             {"success_action_redirect": shop.absolute_settings_url(request)},
             ["starts-with", "$key", key_starts_with],