begin mypy usage - addresses part of pypa#501

.pre-commit-config.yaml

@@ -21,11 +21,18 @@ repos:
     hooks:
     -   id: flake8
 -   repo: https://github.com/asottile/pyupgrade
-    rev: v2.23.1
+    rev: v2.23.3
     hooks:
     - id: pyupgrade
       args: [--py36-plus]
 -   repo: https://github.com/asottile/setup-cfg-fmt
     rev: v1.17.0
     hooks:
     -   id: setup-cfg-fmt
+-   repo: https://github.com/pre-commit/mirrors-mypy
+    rev: 'v0.910'
+    hooks:
+    -   id: mypy
+        additional_dependencies:
+            - types-setuptools
+            - tokenize-rt==3.2.0

mypy.ini

@@ -0,0 +1,9 @@
+[mypy]
+python_version = 3.6
+warn_return_any = True
+warn_unused_configs = True
+mypy_path = $MYPY_CONFIG_FILE_DIR/src
+
+[mypy-setuptools_scm.*]
+# disabled as it will take a bit
+# disallow_untyped_defs = True

src/setuptools_scm/__main__.py

@@ -4,7 +4,7 @@
 from setuptools_scm.integration import find_files
 
 
-def main():
+def main() -> None:
     print("Guessed Version", get_version())
     if "ls" in sys.argv:
         for fname in find_files("."):

src/setuptools_scm/config.py

@@ -8,7 +8,7 @@
 except ImportError:
     import pkg_resources
 
-    Version = pkg_resources.packaging.version.Version
+    Version = pkg_resources.packaging.version.Version  # type: ignore
 
 
 from .utils import trace

src/setuptools_scm/utils.py

@@ -9,7 +9,7 @@
 import sys
 import traceback
 import warnings
-
+from typing import Optional
 
 DEBUG = bool(os.environ.get("SETUPTOOLS_SCM_DEBUG"))
 IS_WINDOWS = platform.system() == "Windows"
@@ -36,14 +36,15 @@ def no_git_env(env):
     }
 
 
-def trace(*k):
+def trace(*k) -> None:
     if DEBUG:
         print(*k)
         sys.stdout.flush()
 
 
-def trace_exception():
-    DEBUG and traceback.print_exc()
+def trace_exception() -> None:
+    if DEBUG:
+        traceback.print_exc()
 
 
 def ensure_stripped_str(str_or_bytes):
@@ -144,12 +145,12 @@ def require_command(name):
 
 
 try:
-    from importlib.metadata import entry_points
+    from importlib.metadata import entry_points  # type: ignore
 except ImportError:
     from pkg_resources import iter_entry_points
 else:
 
-    def iter_entry_points(group, name=None):
+    def iter_entry_points(group: str, name: Optional[str] = None):
         eps = entry_points()[group]
         if name is None:
             return iter(eps)