Add --py37-plus option (#157)

Author: cdce8p

README.md

@@ -107,6 +107,9 @@ Check `git diff` before committing!
 
 ### Python version options
 
+**`--py37-plus`**
+Set the minimum Python syntax version to **3.7**. (Default: **3.8**)
+
 **`--py38-plus`**  
 Set the minimum Python syntax version to **3.8**. This is the default.
 

python_typing_update/__main__.py

@@ -88,9 +88,13 @@ async def async_main(argv: list[str] | None = None) -> int:
     )
 
     group_py_version = py_version_options.add_mutually_exclusive_group()
+    group_py_version.add_argument(
+        '--py37-plus',
+        action='store_const', dest='min_version', const=(3, 7), default=(3, 8),
+    )
     group_py_version.add_argument(
         '--py38-plus',
-        action='store_const', dest='min_version', default=(3, 8), const=(3, 8),
+        action='store_const', dest='min_version', const=(3, 8),
         help="Default"
     )
     group_py_version.add_argument(

tests/test_main.py

@@ -108,6 +108,28 @@ async def test_main(
     await async_test_main(filename, control, argv, returncode, capsys)
 
 
+@pytest.mark.parametrize(
+    ('argv',),
+    (
+        pytest.param(['--py37-plus']),
+        pytest.param(['--py38-plus']),
+        pytest.param(['--py39-plus']),
+        pytest.param(['--py310-plus']),
+    ),
+)
+async def test_py_version(
+    argv: list[str] | None,
+    capsys: CaptureFixture,
+) -> None:
+    await async_test_main(
+        filename='no_changes.py',
+        control='no_changes_no_change.py',
+        argv=argv,
+        returncode=0,
+        capsys=capsys,
+    )
+
+
 @pytest.mark.parametrize(
     ('filename', 'control', 'argv', 'returncode'),
     (