[ python-Bugs-995206 ] Deprecation Warning lies when it cannot parse your encoding

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Bugs item #995206, was opened at 2004-07-21 14:48
Message generated for change (Comment added) made by theller
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Category: None
Group: Python 2.3
Status: Open
Resolution: None
Priority: 5
Submitted By: Laura Creighton (lcreighton)
Assigned to: Nobody/Anonymous (nobody)
Summary: Deprecation Warning lies when it cannot parse your encoding

Initial Comment:
The first line of my python file was:
# -*- coding: 'iso-8859-1' -*-

This is wrong, I need to drop the quotes.  But Python
2.3.4 (#2, Jun 19 2004, 18:15:30) is wrong, also, when it
complains:
sys:1: DeprecationWarning: Non-ASCII character '\xf6'
in file test_stockdict.py on line 14, but no encoding
declared; see http://www.python.org/peps/pep-0263


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>Comment By: Thomas Heller (theller)
Date: 2004-07-21 18:50

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It is even worse - pass the string contents of this file to
compile(), and you get a MemoryError.  See SF # 979739.

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Comment By: Tim Peters (tim_one)
Date: 2004-07-21 18:02

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Laura, you don't *have* an encoding directive here.  You 
thought you were writing one, but it's no more an encoding 
directive than, e.g.,

# I want this to be treated as some form of Finnish.

would have been.  Neither matches the syntax for an 
encoding directive, so both are treated as comments.

You want Python to guess that your line, which matches the 
syntax of a Python comment but not the syntax of an 
encoding directive (and so is treated as a comment), was 
*intended* to be an encoding directive.  That would be 
possible, but first needs a rigorous definition of 
what "intended to look like an encoding directive" means.  
Right now it's a binary "yes or no" decision, based on whether 
one of the first two lines matches (or not) the regexp given in 
the PEP.

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Comment By: M.-A. Lemburg (lemburg)
Date: 2004-07-21 17:44

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Laura, the problem is that the parser only checks for
encoding comments of a certain style. If it doesn't
find that particular style (defined in the PEP), then
is simply goes on with the processing as if there were
no encoding comment (because there isn't ;-).

Quotes are not allowed according to the PEP, so
using them will render the comment useless.

I don't see how the parser could give you a note in
the sense of "well, this may be an encoding comment,
but it is not what I expected, please check".

Of course, patches are welcome if they don't make
the implementation more complicated :-)


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Comment By: Laura Creighton (lcreighton)
Date: 2004-07-21 17:37

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We'll see if this gets me what I want, a comment to
Marc-Andrés comment.

That the parser, which cannot parse my encoding comment
ignores it and tries to continue work, may or may not be
admirable behaviour on the part of the parser.  I'd have
preferred a LookupError or a ValueError, or maybe a 
RuntimeWarning complaining that it couldn't make sense of my
encoding.

But when I get a Deprecation Warning, saying 'no encoding
declared' when there is one, and it's unusable, then that is
the wrong Warning to raise.

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Comment By: M.-A. Lemburg (lemburg)
Date: 2004-07-21 15:20

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I don't see why this should be wrong: if the parser cannot
parse the encoding comment, it simply ignores it and then
continues to work as if no encoding comment were given.


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