Add dev "extras" section with type stubs

.pre-commit-config.yaml

@@ -155,6 +155,10 @@ repos:
     rev: v1.10.0
     hooks:
       - id: mypy
+        # IMPORTANT: Keep type hinting-related dependencies of the
+        # mypy pre-commit hook additional_dependencies in sync with
+        # the dev section of setup.py to avoid discrepancies in type
+        # checking between environments.
         additional_dependencies:
           - types-docopt
           - types-setuptools

requirements-dev.txt

@@ -1,3 +1,4 @@
+--editable .[dev]
 --requirement requirements-test.txt
 ipython
 mypy

setup.py

@@ -93,6 +93,16 @@ def get_version(version_file):
     include_package_data=True,
     install_requires=["docopt", "schema", "setuptools >= 24.2.0"],
     extras_require={
+        # IMPORTANT: Keep type hinting-related dependencies of the dev section
+        # in sync with the mypy pre-commit hook configuration (see
+        # .pre-commit-config.yaml). Any changes to type hinting-related
+        # dependencies here should be reflected in the additional_dependencies
+        # field of the mypy pre-commit hook to avoid discrepancies in type
+        # checking between environments.
+        "dev": [
+            "types-docopt",
+            "types-setuptools",
+        ],
         "test": [
             "coverage",
             # coveralls 1.11.0 added a service number for calls from
@@ -105,7 +115,7 @@ def get_version(version_file):
             "pre-commit",
             "pytest-cov",
             "pytest",
-        ]
+        ],
     },
     # Conveniently allows one to run the CLI tool as `example`
     entry_points={"console_scripts": ["example = example.example:main"]},