I have found a strange failure when run the bigmem tests.

0:20:19 load avg: 1.04 [116/407/1] test_cgitb
test test_cgitb failed -- Traceback (most recent call last):
  File "/home/serhiy/py/cpython/Lib/test/test_cgitb.py", line 23, in test_html
    raise ValueError("Hello World")
ValueError: Hello World

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/serhiy/py/cpython/Lib/test/test_cgitb.py", line 27, in test_html
    html = cgitb.html(sys.exc_info())
  File "/home/serhiy/py/cpython/Lib/cgitb.py", line 117, in html
    records = inspect.getinnerframes(etb, context)
  File "/home/serhiy/py/cpython/Lib/inspect.py", line 1483, in getinnerframes
    frameinfo = (tb.tb_frame,) + getframeinfo(tb, context)
  File "/home/serhiy/py/cpython/Lib/inspect.py", line 1445, in getframeinfo
    lines, lnum = findsource(frame)
  File "/home/serhiy/py/cpython/Lib/inspect.py", line 780, in findsource
    module = getmodule(object, file)
  File "/home/serhiy/py/cpython/Lib/inspect.py", line 739, in getmodule
    f = getabsfile(module)
  File "/home/serhiy/py/cpython/Lib/inspect.py", line 708, in getabsfile
    _filename = getsourcefile(object) or getfile(object)
  File "/home/serhiy/py/cpython/Lib/inspect.py", line 693, in getsourcefile
    if os.path.exists(filename):
  File "/home/serhiy/py/cpython/Lib/genericpath.py", line 19, in exists
    os.stat(path)
ValueError: embedded null byte

0:20:19 load avg: 1.04 [117/407/2] test_csv -- test_cgitb failed


It is not reproduced when run test_cgitb separately.

I bisect the bug manually and using test.bisect. I identified that the bug is triggered when you run the following 3 tests:
---
test.test_imp.ImportTests.test_load_source
test.test_cgitb.TestCgitb.test_html
test.test_cgitb.TestCgitb.test_fonts
---

Write these tests into "tests" file and run:

./python -m test.bisect -uall -M4G test_imp test_cgitb --matchfile=tests

Sorry, run:

./python -m test -M4G test_imp test_cgitb --matchfile=tests

The problem is that imp.load_source() modifies __file__ of the __main__ module.

Example of a file x.py:
---
import imp
import sys
print(sys.modules[__name__])
try:
    imp.load_source(__name__, __file__ + "\0")
except:
    pass
print(sys.modules[__name__])
---

Output:
---
<module '__main__' from 'x.py'>
<module '__main__' from 'x.py\x00'>
---

Attached PR 3871 fixes the side effect in test_imp, but I'm not sure that it's the best fix. Maybe load_source() should use a "transaction" to restore attributes on failure?

load_source() seems to be used imp.reload() for example. Do you expect this function to restore the imported module to its original state on failure?

The whole imp module is deprecated so I'm personally not bothered by imp.load_source() not being strengthened to be more sane.

New changeset a505ecdc5013cd8f930aacc1ec4fb2afa62d3853 by Victor Stinner in branch 'master':
bpo-31676: Fix test_imp.test_load_source() side effect (#3871)
https://github.com/python/cpython/commit/a505ecdc5013cd8f930aacc1ec4fb2afa62d3853

New changeset 178148025494c4058571831fb11fc8eeff8b7365 by Mariatta (Miss Islington (bot)) in branch '3.6':
bpo-31676: Fix test_imp.test_load_source() side effect (GH-3871) (GH-3988)
https://github.com/python/cpython/commit/178148025494c4058571831fb11fc8eeff8b7365

I tested "./python -m test -uall -M4G test_imp test_cgitb" on 3.6 and the master branch. Both tests now pass correctly. I close the issue.