Add a script to validate refactored imports

This script can be removed after imports are refactored and checked
to see that module contents are the same as before or otherwise
non-broken.

This script assumes that module contents are the same as the
contents of their dictionaries, and that all modules in the project
get imported as a consequence of importing the top-level module.
These are both the case currently for GitPython, but they do not
hold for all projects, and may not hold for GitPython at some point
in the future.

.gitignore

@@ -47,3 +47,7 @@ output.txt
 
 # Finder metadata
 .DS_Store
+
+# Output files for modattrs.py (these entries will be removed soon)
+a
+b

modattrs.py

@@ -0,0 +1,53 @@
+#!/usr/bin/env python
+
+"""Script to get the names and "stabilized" reprs of module attributes in GitPython.
+
+Run with :envvar:`PYTHONHASHSEED` set to ``0`` for fully comparable results. These are
+only still meaningful for comparing if the same platform and Python version are used.
+
+The output of this script should probably not be committed, because within the reprs of
+objects found in modules, it may contain sensitive information, such as API keys stored
+in environment variables. The "sanitization" performed here is only for common forms of
+whitespace that clash with the output format.
+"""
+
+# fmt: off
+
+__all__ = ["git", "main"]
+
+import itertools
+import re
+import sys
+
+import git
+
+
+def main():
+    # This assumes `import git` causes all of them to be loaded.
+    gitpython_modules = sorted(
+        (module_name, module)
+        for module_name, module in sys.modules.items()
+        if re.match(r"git(?:\.|$)", module_name)
+    )
+
+    # We will print two blank lines between successive module reports.
+    separators = itertools.chain(("",), itertools.repeat("\n\n"))
+
+    # Report each module's contents.
+    for (module_name, module), separator in zip(gitpython_modules, separators):
+        print(f"{separator}{module_name}:")
+
+        attributes = sorted(
+            (name, value)
+            for name, value in module.__dict__.items()
+            if name != "__all__"  # Because we are deliberately adding these.
+        )
+
+        for name, value in attributes:
+            sanitized_repr = re.sub(r"[\r\n\v\f]", "?", repr(value))
+            normalized_repr = re.sub(r" at 0x[0-9a-fA-F]+", " at 0x...", sanitized_repr)
+            print(f"    {name}:  {normalized_repr}")
+
+
+if __name__ == "__main__":
+    main()