It is common to use glob() as

    glob.glob(os.path.join(basedir, pattern))

But it does not work correctly if the base directory contains special globbing characters ('*', '?', '['). It is an uncommon case, so in most cases the code works. But when move sources to the directory containing special characters, built it and run tests, some tests will fail:

test test_tokenize failed -- Traceback (most recent call last):
  File "/home/serhiy/py/[cpython]/Lib/test/test_tokenize.py", line 1615, in test_random_files
    testfiles.remove(os.path.join(tempdir, "test_unicode_identifiers.py"))
ValueError: list.remove(x): x not in list

test test_multiprocessing_fork failed -- Traceback (most recent call last):
  File "/home/serhiy/py/[cpython]/Lib/test/_test_multiprocessing.py", line 4272, in test_import
    modules = self.get_module_names()
  File "/home/serhiy/py/[cpython]/Lib/test/_test_multiprocessing.py", line 4267, in get_module_names
    modules.remove('multiprocessing.__init__')
ValueError: list.remove(x): x not in list

test test_bz2 failed -- Traceback (most recent call last):
  File "/home/serhiy/py/[cpython]/Lib/test/test_bz2.py", line 740, in testDecompressorChunksMaxsize
    self.assertFalse(bzd.needs_input)
AssertionError: True is not false

test test_multiprocessing_forkserver failed -- Traceback (most recent call last):
  File "/home/serhiy/py/[cpython]/Lib/test/_test_multiprocessing.py", line 4272, in test_import
    modules = self.get_module_names()
  File "/home/serhiy/py/[cpython]/Lib/test/_test_multiprocessing.py", line 4267, in get_module_names
    modules.remove('multiprocessing.__init__')
ValueError: list.remove(x): x not in list

test test_multiprocessing_spawn failed -- Traceback (most recent call last):
  File "/home/serhiy/py/[cpython]/Lib/test/_test_multiprocessing.py", line 4272, in test_import
    modules = self.get_module_names()
  File "/home/serhiy/py/[cpython]/Lib/test/_test_multiprocessing.py", line 4267, in get_module_names
    modules.remove('multiprocessing.__init__')
ValueError: list.remove(x): x not in list

The proposed PR adds glob.escape() to the above code:

    glob.glob(os.path.join(glob.escape(basedir), pattern))

New changeset 935586845815f5b4c7814794413f6a812d4bd45f by Serhiy Storchaka in branch 'master':
bpo-41043: Escape literal part of the path for glob(). (GH-20994)
https://github.com/python/cpython/commit/935586845815f5b4c7814794413f6a812d4bd45f

Would it be worth it to add a "base" keyword argument to glob.glob?

It may be not exactly what you meant, but see issue38144. This issue actually was opened after I looked how that feature can be used in the stdlib and found that most of uses of glob() are vulnerable.

New changeset ecfecc2d6ce88ae71c783f0465a508c6a1b2f2b6 by Serhiy Storchaka in branch '3.9':
[3.9] bpo-41043: Escape literal part of the path for glob(). (GH-20994). (GH-21275)
https://github.com/python/cpython/commit/ecfecc2d6ce88ae71c783f0465a508c6a1b2f2b6

New changeset e73896241e55f452656fd8070eb79f344091bca0 by Serhiy Storchaka in branch '3.8':
[3.8] bpo-41043: Escape literal part of the path for glob(). (GH-20994). (GH-21277)
https://github.com/python/cpython/commit/e73896241e55f452656fd8070eb79f344091bca0