invalid exception handling in Lib/ctypes/macholib/dyld.py

[scoder]

BPO	18893
Nosy	@ronaldoussoren, @amauryfa, @abalkin, @scoder, @methane, @meadori, @berkerpeksag
PRs	[Do Not Merge] Convert Misc/NEWS so that it is managed by towncrier #552
Files	issue18893.diff: 2 to 3 migration for framework_find error handling

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2016-09-26.20:06:40.176>
created_at = <Date 2013-08-31.10:56:26.193>
labels = ['3.7', 'ctypes', 'type-bug', 'library']
title = 'invalid exception handling in Lib/ctypes/macholib/dyld.py'
updated_at = <Date 2017-03-31.16:36:34.551>
user = 'https://github.com/scoder'

bugs.python.org fields:

activity = <Date 2017-03-31.16:36:34.551>
actor = 'dstufft'
assignee = 'none'
closed = True
closed_date = <Date 2016-09-26.20:06:40.176>
closer = 'berker.peksag'
components = ['Library (Lib)', 'ctypes']
creation = <Date 2013-08-31.10:56:26.193>
creator = 'scoder'
dependencies = []
files = ['31560']
hgrepos = []
issue_num = 18893
keywords = ['patch']
message_count = 7.0
messages = ['196629', '196630', '196772', '196807', '277324', '277455', '277456']
nosy_count = 9.0
nosy_names = ['ronaldoussoren', 'amaury.forgeotdarc', 'belopolsky', 'scoder', 'methane', 'meador.inge', 'python-dev', 'berker.peksag', 'madison.may']
pr_nums = ['552']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue18893'
versions = ['Python 2.7', 'Python 3.5', 'Python 3.6', 'Python 3.7']

[scoder]

The exception handling clauses in framework_find() are weird.

def framework_find(fn, executable_path=None, env=None):
    """
    Find a framework using dyld semantics in a very loose manner.

Will take input such as:
    Python
    Python.framework
    Python.framework/Versions/Current
"""
try:
    return dyld_find(fn, executable_path=executable_path, env=env)
except ValueError as e:
    pass
fmwk_index = fn.rfind('.framework')
if fmwk_index == -1:
    fmwk_index = len(fn)
    fn += '.framework'
fn = os.path.join(fn, os.path.basename(fn[:fmwk_index]))
try:
    return dyld_find(fn, executable_path=executable_path, env=env)
except ValueError:
    raise e

My guess is that this is left-over code from Py2.x. Since it doesn't make sense to catch an exception in the second clause just to re-raise it, I think the intention was really to re-raise the original exception caught in the first clause, which no longer works that way in Py3.

The fix would then be to assign the exception to a new variable in the first except clause and re-raise that in the second.

I found this problem because Cython rejected the module with a compile error about "e" being undefined in the last line.

[scoder]

changing title as it doesn't really look like a typo, more a "converto"

[ronaldoussoren]

Your analysis looks correct to me, that is "raise e" is supposed to raise the exception caught by the first try block.

[MadisonMay]

Seems like a simple fix -- patch attached.

[methane]

lgtm

[python-dev]

New changeset e9f34d382eda by Berker Peksag in branch '3.5':
Issue bpo-18893: Fix invalid exception handling in Lib/ctypes/macholib/dyld.py
https://hg.python.org/cpython/rev/e9f34d382eda

New changeset 708337cd8e6a by Berker Peksag in branch '3.6':
Issue bpo-18893: Merge from 3.5
https://hg.python.org/cpython/rev/708337cd8e6a

New changeset b9d9c49d5b50 by Berker Peksag in branch 'default':
Issue bpo-18893: Merge from 3.6
https://hg.python.org/cpython/rev/b9d9c49d5b50

[berkerpeksag]

Thanks!