String with regex comparison in python fails in python

Question

I am trying to compare string with regex in python as follows,

#!/usr/bin/env python3

import re

str1 = "Expecting property name: line \d+ column \d+ (char \d+)"
str2 = "Expecting property name: line 3 column 2 (char 44)"

print(re.search(str1,str2))

if re.search(str1,str2) :
    print("Strings are same")
else :
    print("Strings are different")

I always get following output

None
Strings are different

I am not able to understand what is wrong here.
Can someone suggest/point me what is wrong with this ?

str1 = r"Expecting property name: line \d+ column \d+ $char \d+$" — anubhava
– anubhava, Commented Oct 16, 2018 at 14:42

willeM_ Van Onsem · Accepted Answer · 2018-10-16 14:42:58Z

2

You need to escape the brackets, since otherwise these are seen as "grouping directives" by the regex engine:

str1 = r"Expecting property name: line \d+ column \d+ \(char \d+\)"
#                                                     ^         ^

Note that search does not mean a full match: it simply means a substring of str2 needs to match. So you might want to add ^ and $ anchors.

answered Oct 16, 2018 at 14:42

willeM_ Van Onsem

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3 Comments

ART Over a year ago

Thank you for reply Willem, so final regex string should be r"^Expecting property name: line \d+ column \d+ $char \d+$$" right ?

willeM_ Van Onsem Over a year ago

@AnkurTank: given you want an exact match, yes, but if 'foobar Expecting property name: line 123 column 123 \(char 123) qux other nonsense' is acceptable, then of course you can omit the anchors. It depends on what you want.

ART Over a year ago

Got it.Thanks for help.

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