Replace numbers between parts of string using regex

Question

I want to replace numbers between some part of string

for eg :.

f = "abc 123 def 23435 kill x22 y2986"

I want to replace all umber between def and y with #

Tried using the following expression , it didnt work

exp = re.sub(r"(?<=def)\d+(?=y)", "#", f)

Expected output :

abc 123 def ##### kill x## y2986

That regex matches "def, followed immediately by a digit sequence, followed immediately by a y". Your string has things other than digit sequences between "def" and "y", so it doesn't match. — Kevin
– Kevin, Commented Jan 19, 2018 at 16:14
But isnt there any way that regex can be applied between some words — Jitendra Aswani
– Jitendra Aswani, Commented Jan 19, 2018 at 16:18

riteshtch · Accepted Answer · 2018-01-19 16:31:56Z

4

Well, I think at first glance it seems it is difficult to do it with regex but there is a way to do it by applying regex in multiple levels (in this case 2 levels). Here is an example:

>>> f = "abc 123 def 23435 kill x22 y2986" 
>>> import re
>>> exp = re.sub(r"(?<=def)(.*)(?=y)", lambda x:re.sub(r"\d", '#', x.group()), f)
>>> exp
'abc 123 def ##### kill x## y2986'
>>>

edited Jan 19, 2018 at 16:31

answered Jan 19, 2018 at 16:19

riteshtch

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Nahuel Fouilleul · Accepted Answer · 2018-01-19 16:54:08Z

1

in the general case it is not possible without a variable length lookbehind, however in that particular case it can be done with a positive and a negative lookahead however it may replace digit if there is another y after last y :

\d(?!.*def[^y]*y)(?=[^y]*y)

matches a digit

which is not followed by def[^y]*y : digit is not before def..y
and is followed by [^y]*y : digit is before ..y

check here regex101

answered Jan 19, 2018 at 16:54

Nahuel Fouilleul

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1 Comment

Nahuel Fouilleul Over a year ago

reread my answer ;), it is explained it works only for the case in the question

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