Re: Did Python 3.12 developers honestly broke special regexp sequences? (Was: hatop fails its autopkg tests with Python 3.12)
On Tue, 13 Feb 2024 at 18:21:17 +0100, Andreas Tille wrote:
> SyntaxWarning: invalid escape sequence '\.'
> 573s CLI_INPUT_RE = re.compile('[a-zA-Z0-9_:\.\-\+; /#%]')
This should be:
re.compile(r'[a-zA-Z0-9_:\.\-\+; /#%]')
^
a raw string, where the backslashes are not interpreted by the
Python parser, allowing them to be passed through to the re module for
parsing; or alternatively
re.compile('[a-zA-Z0-9_:\\.\\-\\+; /#%]')
^^ ^^ ^^
like you would have to write in the C equivalent.
Reference:
"""
Regular expressions use the backslash character ('\') to indicate
special forms or to allow special characters to be used without
invoking their special meaning. This collides with Python’s usage
of the same character for the same purpose in string literals;
for example, to match a literal backslash, one might have to write
'\\\\' as the pattern string, because the regular expression must
be \\, and each backslash must be expressed as \\ inside a regular
Python string literal. Also, please note that any invalid escape
sequences in Python’s usage of the backslash in string literals
now generate a SyntaxWarning and in the future this will become a
SyntaxError. This behaviour will happen even if it is a valid escape
sequence for a regular expression.
The solution is to use Python’s raw string notation for regular
expression patterns; backslashes are not handled in any special way
in a string literal prefixed with 'r'. So r"\n" is a two-character
string containing '\' and 'n', while "\n" is a one-character string
containing a newline. Usually patterns will be expressed in Python
code using this raw string notation.
"""
—re module docs
> which makes me scratching my head what else we should write
> for "any kind of space" now in Python3.12.
\s continues to be correct for "any kind of space", but Python now
complains if you do the backslash-escapes in the wrong layer of syntax.
smcv
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