Negating part of a regular expression
xiº
I am trying to build regex to find classes into python code without explicitly inheritance from object.
import re
test_string = '''
class Test(object):
pass
class Test:
pass
'''
regex = r'class .*(?!\(object\)).*'
re.compile(regex).findall(test_string)
Which gives me:
'class Test(object):', 'class Test:'
But I need only 'class Test:'.
At the same time positive lookahead works fine:
>>> print regex = r'class .*(?=\(object\)).*'
['class Test(object):']
What is the problem here?
Wiktor Stribiżew
You need to use the (?!.*\(object\)) negative lookahead after "class ":
class (?!.*\(object\)).*
See the regex demo
The .*(?!\(object\)).* subpattern matches any 0+ characters other than a newline that is not followed with (object). It effectively grabs all the line up to its end, and does not find any (object) after it. The second .* does not even match anything as all the characters already "belong" to the first .*.
In (?!.*\(object\)), the check occurs after consuming class+space, and fails the match once there is an (object) somewhere further on the current line.
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