On 17.03.2016 01:29, Guido van Rossum wrote:
> I've updated the PEP. Please review. I decided not to update the
> Unicode howto (the thing is too obscure). Serhiy, you're probably in a
> better position to fix the code looking for cookies to pick the first
> one if there are two on the same line (or do whatever you think should
> be done there).
Thanks, will do.
> Should we recommend that everyone use tokenize.detect_encoding()?
I'd prefer a separate utility for this somewhere, since
tokenize.detect_encoding() is not available in Python 2.
I've attached an example implementation with tests, which works
in Python 2.7 and 3.
> On Wed, Mar 16, 2016 at 5:05 PM, Guido van Rossum <[email protected]> wrote:
>> On Wed, Mar 16, 2016 at 12:59 AM, M.-A. Lemburg <[email protected]> wrote:
>>> The only reason to read up to two lines was to address the use of
>>> the shebang on Unix, not to be able to define two competing
>>> source code encodings :-)
>>
>> I know. I was just surprised that the PEP was sufficiently vague about
>> it that when I found that mypy picked the second if there were two, I
>> couldn't prove to myself that it was violating the PEP. I'd rather
>> clarify the PEP than rely on the reasoning presented earlier here.
I suppose it's a rather rare case, since it's the first time
that I heard about anyone thinking that a possible second line
could be picked - after 15 years :-)
>> I don't like erroring out when there are two different cookies on two
>> lines; I feel that the spirit of the PEP is to read up to two lines
>> until a cookie is found, whichever comes first.
>>
>> I will update the regex in the PEP too (or change the wording to avoid
>> "match").
>>
>> I'm not sure what to do if there are two cooking on one line. If
>> CPython currently picks the latter we may want to preserve that
>> behavior.
>>
>> Should we recommend that everyone use tokenize.detect_encoding()?
>>
>> --
>> --Guido van Rossum (python.org/~guido)
>
>
>
--
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#!/usr/bin/python
"""
Utility to detect the source code encoding of a Python file.
Marc-Andre Lemburg, 2016.
Supports Python 2.7 and 3.
"""
import sys
import re
import codecs
# Debug output ?
_debug = True
# PEP 263 RE
PEP263 = re.compile(b'^[ \t]*#.*?coding[:=][ \t]*([-.a-zA-Z0-9]+)',
re.MULTILINE)
###
def detect_source_encoding(code, buffer_size=400):
""" Detect and return the source code encoding of the Python code
given in code.
code must be given as bytes.
The function uses a buffer to determine the first two code lines
with a default size of 400 bytes/code points. This can be adjusted
using the buffer_size parameter.
"""
# Get the first two lines
first_two_lines = b'\n'.join(code[:buffer_size].splitlines()[:2])
# BOMs override any source code encoding comments
if first_two_lines.startswith(codecs.BOM):
return 'utf-8'
# .search() picks the first occurrance
m = PEP263.search(first_two_lines)
if m is None:
return 'ascii'
return m.group(1).decode('ascii')
# Tests
def _test():
l = (
(b"""\
# No encoding
""", 'ascii'),
(b"""\
# coding: latin-1
""", 'latin-1'),
(b"""\
#!/usr/bin/python
# coding: utf-8
""", 'utf-8'),
(b"""\
coding=123
# The above could be detected as source code encoding
""", 'ascii'),
(b"""\
# coding: latin-1
# coding: utf-8
""", 'latin-1'),
(b"""\
# No encoding on first line
# No encoding on second line
# coding: utf-8
""", 'ascii'),
(codecs.BOM + b"""\
# No encoding
""", 'utf-8'),
(codecs.BOM + b"""\
# BOM and encoding
# coding: latin-1
""", 'utf-8'),
)
for code, encoding in l:
if _debug:
print ('=' * 72)
print ('Checking:')
print ('-' * 72)
print (code.decode('latin-1'))
print ('-' * 72)
detected_encoding = detect_source_encoding(code)
if _debug:
print ('detected: %s, expected: %s' %
(detected_encoding, encoding))
assert detected_encoding == encoding
if __name__ == '__main__':
_test()
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