Python - how to split a string using regex but preserving pattern that contains the split separator?

Question

Starting from "param1=1-param2=1.e-01-param3=A", how to get
["param1=1", "param2=1.e-01", "param3=A"] ? The problem is that the separator "-" may be contained in the value of a parameter.

Franck

>>> import re
>>> re.split("-", "param1=1-param2=1.e-01-param3=A")
['param1=1', 'param2=1.e', '01', 'param3=A']
>>> re.split("[^e]-[^0]", "param1=1-param2=1.e-01-param3=A")
['param1=', 'aram2=1.e-0', 'aram3=A']
>>> re.split("[?^e]-[?^0]", "param1=1-param2=1.e-01-param3=A")
['param1=1-param2=1.', '1-param3=A']

EDIT

OK, I forgot to mention param1, param2, param3 do actually not share the same "param" string. What about if we have to split "p=1-q=1.e-01-r=A"into the same kind of list ["p=1", "q=1.e-01", "r=A"] ?

EDIT

>>> re.split("(?:-)(?=[a-z]+)", "p=1-q=1.e-01-r=A")
['p=1', 'q=1.e-01', 'r=A']

Does the job for me as I know parameter names can not carry any -.

Thanks, guys !

DeepSpace · Accepted Answer · 2017-07-20 10:43:06Z

2

By using non-capturing group and positive lookahead, capture '-' only if it is followed by 'param':

import re

string = "param1=1-param2=1.e-01-param3=A"
print(re.split(r"(?:-)(?=param)", string))
# ['param1=1', 'param2=1.e-01', 'param3=A']

Live demo on regex101

answered Jul 20, 2017 at 10:43

DeepSpace

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2 Comments

fghoussen Over a year ago

Thanks, I didn't know about non-capturing group and positive lookahead: still need to read on these notions. Could you detail a bit further the meaning of both (?:-) and (?=param) in this case ?

DeepSpace Over a year ago

(?:-) will make sure the - isn't actually captured (otherwise the returned list would be ['param1=1', '-', 'param2=1.e-01', '-', 'param3=A'], and (?=param) will make sure to only capture '-' that have param after them (so - in a middle of a param value will not match)

Ajay2588 · Accepted Answer · 2017-07-20 12:29:29Z

0

For other strings,

Try out this https://regex101.com/r/zwI2Mk/1 and https://regex101.com/r/zwI2Mk/1/codegen?language=python

answered Jul 20, 2017 at 12:29

Ajay2588

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1 Comment

DeepSpace Over a year ago

This will fail if a value is string that contains -

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