How do i write a regular expression for the following pattern in python?
How do i look for the following pattern using regular expression in python? for the two cases
Am looking for str2 after the "=" sign
- Case 1:
str1=str2 - Case 2:
str1 = str2
please note there can be a space or none between the either side of the "=" sign
Mine is like this, but only works for one of the cases!
m=re.search('(?<=str\s\=\s)\w+','str = str2')
returns str2
Help!
Gath
Asked by: Wilson384 | Posted: 06-12-2021
Answer 1
if you indeed have only such simple strings to parse you don't need regular expression. you can just partition on = and strip (or even lstrip) last element of a resulting tuple:
>>> case = 'str = str2'
>>> case.partition('=')[2].lstrip()
'str2'
it'll be much faster than regexps. and just to show how fast i've made a simple test:
>>> timeit.timeit("'str1 = str2 '.partition('=')[2].strip()")
0.49051564213846177
>>> timeit.timeit("'str1 = str2 '.split('=')[1].strip()")
0.97673281637025866
>>> timeit.timeit('import re')
0.65663786250422618
Answer 2
re.search(r'=\s*(.*)', 'str = str2').group(1)
or if you just want a single word:
re.search(r'=\s*(\w+)', 'str = str2').group(1)
Extended to specific initial string:
re.search(r'\bstr\s*=\s*(\w+)', 'str=str2').group(1)
\b = word boundary, so won't match "somestr=foo"
It would be quicker to go trough all options once, instead of searching for single options one at the time:
option_str = "a=b, c=d, g=h"
options = dict(re.findall(r'(\w+)\s*=\s*(\w+)', option_str))
options['c'] # -> 'd'
Answer 3
If your data is fixed then you can do this without using regex. Just split it on '='. For example:
>>> case1 = "str1=str2"
>>> case2 = "str1 = str2"
>>> str2 = case1.split('=')[1].strip()
>>> str2 = case2.split('=')[1].strip()
This YOURCASE.split('=')[1].strip() statement will work for any cases.
Answer 4
Simply use split function
Answered by: Edgar602 | Posted: 07-01-2022Answer 5
Expanding on @batbrat's answer, and the other suggestions, you can use re.split() to separate the input string. The pattern can use \s (whitespace) or an explicit space.
>>> import re
>>> c1="str1=str2"
>>> c2="str1 = str2"
>>> re.split(' ?= ?',c1)
['str1', 'str2']
>>> re.split(' ?= ?',c2)
['str1', 'str2']
>>> re.split(r'\s?=\s?',c1)
['str1', 'str2']
>>> re.split(r'\s?=\s?',c2)
['str1', 'str2']
>>>
Answer 6
I think a regex is overkill if you only want to deal with the above two cases. Here's what I'd do-
>>> case1 = "str1=str2"
>>> case2 = "str1 = str2"
>>> case2.split()
['str1', '=', 'str2']
>>> ''.join(case2.split())
'str1=str2'
>>> case1[5:]
'str2'
>>> ''.join(case2.split())[5:]
'str2'
>>>
Assumption
I assume you are looking for the specific token 'str1'. I also assume that str1 can be assigned different values. Something like what you'd have in a configuration file => propertyName = value.
This is just my opinion.
I knew that other ways were possible! SilentGhost gives a nice (better!) alternative.
Hope this helps.
Answered by: Anna126 | Posted: 07-01-2022Answer 7
Two cases:
(case 1) if there is a single space before the '=', then there must also be a single space after the '='
m=re.search(r'(?<=\S)(?:\s=\s|=)(\w+)','str = str2') print m.group(1)(case 2) otherwise,
m=re.search(r'(?<=\S)\s?=\s?(\w+)','str = str2') print m.group(1)
In the first case, you could also use the "(?P=…" construct for the second space or lack of it, but it still wouldn't work for a positive lookbehind assertion, since it wouldn't be a constant length subexpression.
Answered by: Brad630 | Posted: 07-01-2022Answer 8
Related idea: I find using graphical regular expression tool helpful when trying to figure out correct pattern: http://kodos.sf.net.
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