Fixing some byte-to-string conversion warnings

[eng793]

BPO	15845
Nosy	@pitrou, @benjaminp, @ezio-melotti, @serhiy-storchaka
Files	os_glob_bytes.patch: patch

^{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 = 'https://github.com/serhiy-storchaka'
closed_at = <Date 2013-01-08.09:43:37.892>
created_at = <Date 2012-09-02.02:19:56.305>
labels = ['type-bug', 'library']
title = 'Fixing some byte-to-string conversion warnings'
updated_at = <Date 2013-01-08.09:43:37.891>
user = 'https://bugs.python.org/eng793'

bugs.python.org fields:

activity = <Date 2013-01-08.09:43:37.891>
actor = 'serhiy.storchaka'
assignee = 'serhiy.storchaka'
closed = True
closed_date = <Date 2013-01-08.09:43:37.892>
closer = 'serhiy.storchaka'
components = ['Library (Lib)']
creation = <Date 2012-09-02.02:19:56.305>
creator = 'eng793'
dependencies = []
files = ['27092']
hgrepos = []
issue_num = 15845
keywords = ['patch']
message_count = 7.0
messages = ['169683', '169735', '170868', '177608', '179278', '179325', '179326']
nosy_count = 6.0
nosy_names = ['pitrou', 'benjamin.peterson', 'ezio.melotti', 'python-dev', 'serhiy.storchaka', 'eng793']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue15845'
versions = ['Python 3.2', 'Python 3.3', 'Python 3.4']

[eng793]

This is related to bpo-15826.

When run with the -b option, some glob.py and os.py functions give warnings due to byte-to-string conversions:

amoura@amoura-laptop:/cpython$ ./python -b -c "import glob; glob.glob(b'cover*/glob.cover')"
/home/amoura/cpython/Lib/glob.py:64: BytesWarning: Comparison between bytes and string
if basename == '':
amoura@amoura-laptop:/cpython$ ./python -b -c "import os; os.makedirs(b'tst/making/dirs')"
/home/amoura/cpython/Lib/os.py:266: BytesWarning: Comparison between bytes and string
if tail == cdir: # xxx/newdir/. exists if xxx/newdir exists

The attached patch fixes this.

There is a rather more mysterious phenomenon with exceptions (which is triggered by test_exceptions for ImportException, but it happens for any Exception class):

>>> e = Exception(b'aaa')
[60596 refs]
>>> e.args[0]
b'aaa'
[60601 refs]
>>> str(e)
__main__:1: BytesWarning: str() on a bytes instance
"b'aaa'"
[60615 refs]
>>> e.args[0]
b'aaa'
[60615 refs]
>>> str(e)
"b'aaa'"
[60615 refs]
>>> e.args[0]
b'aaa'
[60615 refs]

In other words, if a bytes argument is given to the exception, the first call to str triggers the warning, but further calls don't. Is this worth pursuing?

[benjaminp]

Not repeating warnings from the same place is the default warning behavior. You can get all of them by passing -Wall.

[ezio-melotti]

• if basename == '':
  + if len(basename) == 0:

This should be "if not basename:"

-        if tail == curdir:
+        cdir = curdir
+        if isinstance(tail, bytes):
+            cdir = bytes(curdir, 'ASCII')
+        if tail == cdir:

This will raise an error if curdir is a non-ascii str, so, unless the same error was already raised later in the code, this is backward incompatible.

[serhiy-storchaka]

The first bug fixed in bpo-16696.

[serhiy-storchaka]

This will raise an error if curdir is a non-ascii str, so, unless the same error was already raised later in the code, this is backward incompatible.

On all supported platforms curdir is a ascii str (':' on Mac Classic, '.' on all other). The same idiom used in glob module.

[python-dev]

New changeset 9458a516f769 by Serhiy Storchaka in branch '3.2':
Issue bpo-15845: Fix comparison between bytes and string.
http://hg.python.org/cpython/rev/9458a516f769

New changeset f6cf2985348a by Serhiy Storchaka in branch '3.3':
Issue bpo-15845: Fix comparison between bytes and string.
http://hg.python.org/cpython/rev/f6cf2985348a

New changeset 51e60d9ee389 by Serhiy Storchaka in branch 'default':
Issue bpo-15845: Fix comparison between bytes and string.
http://hg.python.org/cpython/rev/51e60d9ee389

[serhiy-storchaka]

Fixed. Thank your for report and patch, Alessandro.