gh-148823: Avoid importing _colorize when creating an ArgumentParser

Lib/argparse.py

@@ -92,6 +92,8 @@
 from gettext import gettext as _
 from gettext import ngettext
 
+lazy import _colorize
+
 SUPPRESS = '==SUPPRESS=='
 
 OPTIONAL = '?'
@@ -156,6 +158,15 @@ def _identity(value):
 # Formatting Help
 # ===============
 
+class _ColorlessTheme:
+    # A 'fake' theme for no colors
+    def __getattr__(self, name):
+        # _colorize's no_color themes are just all empty strings
+        # by directly using empty strings the import is avoided
+        return ""
+
+_colorless_theme = _ColorlessTheme()
+
 
 class HelpFormatter(object):
     """Formatter for generating usage messages and argument help strings.
@@ -196,14 +207,32 @@ def __init__(
         self._set_color(False)
 
     def _set_color(self, color, *, file=None):
-        from _colorize import can_colorize, decolor, get_theme
-
-        if color and can_colorize(file=file):
-            self._theme = get_theme(force_color=True).argparse
-            self._decolor = decolor
+        # Set a new color setting and file, clear caches for theme and decolor
+        self._theme_color = color
+        self._theme_file = file
+        self._cached_theme = None
+        self._cached_decolor = None
+
+    def _get_theme_and_decolor(self):
+        # If self._theme_color is false, this prevents _colorize from importing
+        if self._theme_color and _colorize.can_colorize(file=self._theme_file):
+            self._cached_theme = _colorize.get_theme(force_color=True).argparse
+            self._cached_decolor = _colorize.decolor
         else:
-            self._theme = get_theme(force_no_color=True).argparse
-            self._decolor = _identity
+            self._cached_theme = _colorless_theme
+            self._cached_decolor = _identity
+
+    @property
+    def _theme(self):
+        if self._cached_theme is None:
+            self._get_theme_and_decolor()
+        return self._cached_theme
+
+    @property
+    def _decolor(self):
+        if self._cached_decolor is None:
+            self._get_theme_and_decolor()
+        return self._cached_decolor
 
     # ===============================
     # Section and indentation methods
@@ -2856,12 +2885,11 @@ def _print_message(self, message, file=None):
                 pass
 
     def _get_theme(self, file=None):
-        from _colorize import can_colorize, get_theme
-
-        if self.color and can_colorize(file=file):
-            return get_theme(force_color=True).argparse
+        # If self.color is False, _colorize is not imported
+        if self.color and _colorize.can_colorize(file=file):
+            return _colorize.get_theme(force_color=True).argparse
         else:
-            return get_theme(force_no_color=True).argparse
+            return _colorless_theme
 
     # ===============
     # Exiting methods

Lib/test/support/import_helper.py

@@ -325,7 +325,7 @@ def ready_to_import(name=None, source=""):
                 sys.modules.pop(name, None)
 
 
-def ensure_lazy_imports(imported_module, modules_to_block):
+def ensure_lazy_imports(imported_module, modules_to_block, *, additional_code=None):
     """Test that when imported_module is imported, none of the modules in
     modules_to_block are imported as a side effect."""
     modules_to_block = frozenset(modules_to_block)
@@ -343,6 +343,16 @@ def ensure_lazy_imports(imported_module, modules_to_block):
             raise AssertionError(f'unexpectedly imported after importing {imported_module}: {{after}}')
         """
     )
+    if additional_code:
+        script += additional_code
+        script += textwrap.dedent(
+            f"""
+            if unexpected := modules_to_block & sys.modules.keys():
+                after = ", ".join(unexpected)
+                raise AssertionError(f'unexpectedly imported after additional code: {{after}}')
+            """
+        )
+
     from .script_helper import assert_python_ok
     assert_python_ok("-S", "-c", script)
 

Lib/test/test_argparse.py

@@ -80,6 +80,49 @@ def test_skip_invalid_stdout(self):
                 self.assertRegex(mocked_stderr.getvalue(), r'usage:')
 
 
+class TestLazyImports(unittest.TestCase):
+    LAZY_IMPORTS = {
+        "_colorize",
+        "copy",
+        "difflib",
+        "shutil",
+        "textwrap",
+        "warnings",
+    }
+    def test_module_import(self):
+        import_helper.ensure_lazy_imports(
+            "argparse",
+            self.LAZY_IMPORTS,
+        )
+
+    def test_create_parser(self):
+        # Test imports are still unused after
+        # creating a parser
+        create_parser = "argparse.ArgumentParser()"
+        imported_modules = {"shutil"}
+
+        import_helper.ensure_lazy_imports(
+            "argparse",
+            self.LAZY_IMPORTS - imported_modules,
+            additional_code=create_parser,
+        )
+
+    def test_add_subparser(self):
+        add_subparser = textwrap.dedent(
+            f"""
+            parser = argparse.ArgumentParser()
+            parser.add_subparsers(dest='command', required=False)
+            """
+        )
+        imported_modules = {"shutil"}
+
+        import_helper.ensure_lazy_imports(
+            "argparse",
+            self.LAZY_IMPORTS - imported_modules,
+            additional_code=add_subparser,
+        )
+
+
 class TestArgumentParserPickleable(unittest.TestCase):
 
     @force_not_colorized