diff --git a/AUTHORS b/AUTHORS
index 108baa8..9661ac9 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -3,4 +3,5 @@ Gilles Fabio
 Jannis Leidel
 Marc Abramowitz
 Michael van Tellingen
-Mike Fogel
\ No newline at end of file
+Mike Fogel
+Peter Bittner
diff --git a/README.rst b/README.rst
index c80f72c..faf46ed 100644
--- a/README.rst
+++ b/README.rst
@@ -32,6 +32,12 @@ Install django-configurations:
 
     pip install django-configurations
 
+or, alternatively, if you want to use URL-based values:
+
+.. code-block:: console
+
+    pip install django-configurations[cache,database,email,search]
+
 Then subclass the included ``configurations.Configuration`` class in your
 project's **settings.py** or any other module you're using to store the
 settings constants, e.g.:
diff --git a/configurations/importer.py b/configurations/importer.py
index f9dfd6c..e43f2b8 100644
--- a/configurations/importer.py
+++ b/configurations/importer.py
@@ -124,8 +124,8 @@ class ConfigurationImporter(object):
                 def stylize(text):
                     return colorize(text, fg='green')
 
-            if (self.argv[1] == 'runserver' and
-                    os.environ.get('RUN_MAIN') == 'true'):
+            if self.argv[1] == 'runserver' \
+                    and os.environ.get('RUN_MAIN') == 'true':
 
                 message = ("django-configurations version {0}, using "
                            "configuration '{1}'".format(__version__,
diff --git a/configurations/values.py b/configurations/values.py
index 056e9a0..af53b62 100644
--- a/configurations/values.py
+++ b/configurations/values.py
@@ -52,8 +52,8 @@ class Value(object):
             instance.late_binding = kwargs.get('late_binding')
         if not instance.late_binding:
             instance.__init__(*args, **kwargs)
-            if ((instance.environ and instance.environ_name) or
-                    (not instance.environ and instance.default)):
+            if (instance.environ and instance.environ_name) \
+                    or (not instance.environ and instance.default):
                 instance = instance.setup(instance.environ_name)
         return instance
 
diff --git a/setup.py b/setup.py
index 06fd946..7a2efdf 100644
--- a/setup.py
+++ b/setup.py
@@ -41,6 +41,22 @@ setup(
             'django-cadmin = configurations.management:execute_from_command_line',
         ],
     },
+    extras_require={
+        'cache': ['django-cache-url'],
+        'database': ['dj-database-url'],
+        'email': ['dj-email-url'],
+        'search': ['dj-search-url'],
+        'testing': [
+            'django-discover-runner',
+            'mock',
+            'django-cache-url>=1.0.0',
+            'dj-database-url',
+            'dj-email-url',
+            'dj-search-url',
+            'six',
+            'Sphinx>=1.4',
+        ],
+    },
     classifiers=[
         'Development Status :: 5 - Production/Stable',
         'Framework :: Django',
@@ -49,10 +65,9 @@ setup(
         'Operating System :: OS Independent',
         'Programming Language :: Python',
         'Programming Language :: Python :: 2.7',
-        'Programming Language :: Python :: 3.2',
-        'Programming Language :: Python :: 3.4',
         'Programming Language :: Python :: 3.5',
         'Programming Language :: Python :: 3.6',
+        'Programming Language :: Python :: 3.7',
         'Topic :: Utilities',
     ],
     zip_safe=False,
diff --git a/tests/requirements.txt b/tests/requirements.txt
deleted file mode 100644
index f62636b..0000000
--- a/tests/requirements.txt
+++ /dev/null
@@ -1,8 +0,0 @@
-django-discover-runner
-mock
-dj-database-url
-dj-email-url
-dj-search-url
-django-cache-url>=1.0.0
-six
-Sphinx>=1.4
diff --git a/tox.ini b/tox.ini
index cca6f96..5f3454b 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,8 +1,8 @@
 [tox]
-skipsdist = True
-usedevelop = True
+skipsdist = true
+usedevelop = true
 minversion = 1.8
-whitelist_externals=sphinx-build
+whitelist_externals = sphinx-build
 envlist =
     flake8-py27,
     flake8-py36,
@@ -19,7 +19,6 @@ setenv =
     coverage: COVERAGE_PROCESS_START = {toxinidir}/setup.cfg
     coverage: _TEST_RUN_PREFIX=coverage run
 deps =
-    -rtests/requirements.txt
     dj18: django>=1.8,<1.9
     dj110: django>=1.10,<1.11
     dj111: django>=1.11,<2.0
@@ -29,7 +28,7 @@ deps =
     py27,pypy: mock
     coverage: coverage
     coverage: coverage_enable_subprocess
-
+extras = testing
 commands =
     python --version
     {env:_TEST_RUN_PREFIX:} {envbindir}/django-cadmin test -v2 {posargs:tests}
@@ -49,5 +48,5 @@ commands = flake8 configurations tests
 deps = flake8
 
 [flake8]
-exclude=.tox
-ignore=E501,E127,E128,E124
+exclude = .tox
+ignore = E501,E127,E128,E124