[New-bugs-announce] [issue33224] "RuntimeError: generator raised StopIteration" in difflib.mdiff

[Jeff Kaufman]

New submission from Jeff Kaufman <jeff.t.kaufman at gmail.com>:

With python built at HEAD (c51d8c9b) and at 3.7b3 (fcd4e03e08) the code:

    import difflib
    for fromdata, todata, flag in difflib._mdiff(
        ["2"], ["3"], 1):
      pass

produces:

    Traceback (most recent call last):
      File "/home/jefftk/cpython/Lib/difflib.py", line 1638, in _mdiff
        from_line, to_line, found_diff = next(line_pair_iterator)
    StopIteration

    The above exception was the direct cause of the following exception:

    Traceback (most recent call last):
      File "/home/jefftk/icdiff/repro.py", line 3, in <module>
        ["2"], ["3"], 1):
    RuntimeError: generator raised StopIteration

In python 3.5 and 3.6 I don't get an error.

This is probably due to https://bugs.python.org/issue32670 which implements PEP 479, but I this this isn't supposed to happen in library code?

----------
components: Library (Lib)
messages: 314936
nosy: Jeff.Kaufman
priority: normal
severity: normal
status: open
title: "RuntimeError: generator raised StopIteration" in difflib.mdiff
type: behavior
versions: Python 3.7

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue33224>
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