diff --git a/.flake8 b/.flake8
index d514d9f38fb..a229cfef0ad 100644
--- a/.flake8
+++ b/.flake8
@@ -1,3 +1,3 @@
 [flake8]
-ignore = E125,D100,D101,D102,D105,D200,D211,P101,FI15,FI16,FI12,FI11,FI17,FI50,FI53,FI54
+ignore = E125,D100,D101,D102,D105,D107,D200,D211,P101,FI15,FI16,FI12,FI11,FI17,FI50,FI53,FI54
 max-line-length = 80
diff --git a/.isort.cfg b/.isort.cfg
index 773d50df372..fc9d00977de 100644
--- a/.isort.cfg
+++ b/.isort.cfg
@@ -3,8 +3,7 @@ line_length=80
 indent='    '
 multi_line_output=4
 default_section=FIRSTPARTY
-known_readthedocs=readthedocs
-known_readthedocsinc=readthedocsinc
-known_third_party=celery,stripe,requests,pytz,builtins,django,annoying
+known_firstparty=readthedocs,readthedocsinc
+known_third_party=celery,stripe,requests,pytz,builtins,django,annoying,readthedocs_build
 sections=FUTURE,STDLIB,THIRDPARTY,FIRSTPARTY,LOCALFOLDER
 add_imports=from __future__ import division, from __future__ import print_function, from __future__ import unicode_literals
diff --git a/readthedocs/doc_builder/config.py b/readthedocs/doc_builder/config.py
index d6bf0fa516e..2ce1db0ad9c 100644
--- a/readthedocs/doc_builder/config.py
+++ b/readthedocs/doc_builder/config.py
@@ -1,11 +1,14 @@
+# -*- coding: utf-8 -*-
 """An API to load config from a readthedocs.yml file."""
-from __future__ import absolute_import
 
-from builtins import (filter, object)
+from __future__ import (
+    absolute_import, division, print_function, unicode_literals)
 
-from readthedocs_build.config import (ConfigError, BuildConfig, InvalidConfig,
-                                      load as load_config)
-from .constants import BUILD_IMAGES, DOCKER_IMAGE
+from builtins import filter, object
+from readthedocs_build.config import load as load_config
+from readthedocs_build.config import BuildConfig, ConfigError, InvalidConfig
+
+from .constants import DOCKER_BUILD_IMAGES, DOCKER_IMAGE
 
 
 class ConfigWrapper(object):
@@ -18,7 +21,6 @@ class ConfigWrapper(object):
     We only currently implement a subset of the existing YAML config.
     This should be the canonical source for our usage of the YAML files,
     never accessing the config object directly.
-
     """
 
     def __init__(self, version, yaml_config):
@@ -53,10 +55,12 @@ def python_interpreter(self):
         if ver in [2, 3]:
             # Get the highest version of the major series version if user only
             # gave us a version of '2', or '3'
-            ver = max(list(filter(
-                lambda x: x < ver + 1,
-                self._yaml_config.get_valid_python_versions(),
-            )))
+            ver = max(
+                list(
+                    filter(
+                        lambda x: x < ver + 1,
+                        self._yaml_config.get_valid_python_versions(),
+                    )))
         return 'python{0}'.format(ver)
 
     @property
@@ -118,8 +122,8 @@ def load_yaml_config(version):
     """
     Load a configuration from `readthedocs.yml` file.
 
-    This uses the configuration logic from `readthedocs-build`,
-    which will keep parsing consistent between projects.
+    This uses the configuration logic from `readthedocs-build`, which will keep
+    parsing consistent between projects.
     """
     checkout_path = version.project.checkout_path(version.slug)
     env_config = {}
@@ -127,9 +131,9 @@ def load_yaml_config(version):
     # Get build image to set up the python version validation. Pass in the
     # build image python limitations to the loaded config so that the versions
     # can be rejected at validation
-    build_image = BUILD_IMAGES.get(
+    build_image = DOCKER_BUILD_IMAGES.get(
         version.project.container_image,
-        BUILD_IMAGES.get(DOCKER_IMAGE, None),
+        DOCKER_BUILD_IMAGES.get(DOCKER_IMAGE, None),
     )
     if build_image:
         env_config = {
@@ -147,7 +151,8 @@ def load_yaml_config(version):
             path=checkout_path,
             env_config=sphinx_env_config,
         )[0]
-    except InvalidConfig:  # This is a subclass of ConfigError, so has to come first
+    except InvalidConfig:
+        # This is a subclass of ConfigError, so has to come first
         raise
     except ConfigError:
         config = BuildConfig(
diff --git a/readthedocs/doc_builder/constants.py b/readthedocs/doc_builder/constants.py
index 4e96b7ddc6d..18caa705028 100644
--- a/readthedocs/doc_builder/constants.py
+++ b/readthedocs/doc_builder/constants.py
@@ -1,22 +1,36 @@
-"""Doc build constants"""
+# -*- coding: utf-8 -*-
+"""Doc build constants."""
+
+from __future__ import (
+    absolute_import, division, print_function, unicode_literals)
 
-from __future__ import absolute_import
 import os
 import re
 
 from django.conf import settings
 
-
-SPHINX_TEMPLATE_DIR = os.path.join(settings.SITE_ROOT, 'readthedocs',
-                                   'templates', 'sphinx')
-MKDOCS_TEMPLATE_DIR = os.path.join(settings.SITE_ROOT, 'readthedocs',
-                                   'templates', 'mkdocs')
+SPHINX_TEMPLATE_DIR = os.path.join(
+    settings.SITE_ROOT,
+    'readthedocs',
+    'templates',
+    'sphinx',
+)
+MKDOCS_TEMPLATE_DIR = os.path.join(
+    settings.SITE_ROOT,
+    'readthedocs',
+    'templates',
+    'mkdocs',
+)
 SPHINX_STATIC_DIR = os.path.join(SPHINX_TEMPLATE_DIR, '_static')
 
 PDF_RE = re.compile('Output written on (.*?)')
 
 # Docker
-DOCKER_SOCKET = getattr(settings, 'DOCKER_SOCKET', 'unix:///var/run/docker.sock')
+DOCKER_SOCKET = getattr(
+    settings,
+    'DOCKER_SOCKET',
+    'unix:///var/run/docker.sock',
+)
 DOCKER_VERSION = getattr(settings, 'DOCKER_VERSION', 'auto')
 DOCKER_IMAGE = getattr(settings, 'DOCKER_IMAGE', 'readthedocs/build:2.0')
 DOCKER_LIMITS = {'memory': '200m', 'time': 600}
@@ -28,7 +42,7 @@
 DOCKER_HOSTNAME_MAX_LEN = 64
 
 # Build images
-BUILD_IMAGES = {
+DOCKER_BUILD_IMAGES = {
     'readthedocs/build:1.0': {
         'python': {'supported_versions': [2, 2.7, 3, 3.4]},
     },
@@ -39,3 +53,4 @@
         'python': {'supported_versions': [2, 2.7, 3, 3.3, 3.4, 3.5, 3.6]},
     },
 }
+DOCKER_BUILD_IMAGES.update(getattr(settings, 'DOCKER_BUILD_IMAGES', {}))