python regular expression to remove specific sub_string from the string

Question

i want to remove all sort_by=<string> from the variable get_params.

the get_params will be either ?sort_by=name&role=user or ?gender=male&sort_by=name_desc&role=user or '?sort_by=name'

and i want something output like this

i tried this

re.sub("^sort_by=&*$",r'', get_params)

but its not working .

i looked into many answers in stackoverflow but i couldnt do it

Try re.sub(r'\?sort_by=[^&]*$|(?<=[?&])sort_by=[^&]*&', '', get_params) — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Oct 25, 2018 at 14:23
@WiktorStribiżew thanks for helping me. if the variable is ?age=24&sort_by=fullname&gender=male then the result is ?age=24&&gender=male double & is comming . Is there any way to remove it . — tstudent
– tstudent, Commented Oct 25, 2018 at 14:26
My comment has been updated. Actually, I see I need to make last & optional. Use re.sub(r'\?sort_by=[^&]*$|(?<=[?&])sort_by=[^&]*&?', '', get_params). See this demo. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Oct 25, 2018 at 14:28
i really apprectiate your help ...thanks a loot... if you dont mind could you please explain a bit about this regex .. — tstudent
– tstudent, Commented Oct 25, 2018 at 14:56
sorry @WiktorStribiżew i got it from the demo link.. thanks a lot..... — tstudent
– tstudent, Commented Oct 25, 2018 at 15:04

Wiktor Stribiżew · Accepted Answer · 2018-10-25 16:46:18Z

You may use

[?&]sort_by=[^&]*$|(?<=[?&])sort_by=[^&]*&

to replace with an empty string. See the regex demo online.

It matches

[?&] - a ? or &
sort_by= - a literal substring
[^&]* - 0+ chars other than &
$ - end of string.
| - or
(?<=[?&]) - a location preceded with ? or &
sort_by= - a literal substring
[^&]* - 0+ chars other than &
& - a & char.

A Python demo:

key_to_remove = r'sort_by'
rx = r'[?&]{0}=[^&]*$|(?<=[?&]){0}=[^&]*&'.format(key_to_remove)
tests = ['?sort_by=name&role=user','?gender=male&sort_by=name_desc&role=user','?sort_by=name','?age=24&sort_by=fullname&gender=male','?age=24&sort_by=fullname']
for test in tests:
    print(test + " => " + re.sub(rx, "", test))

Output:

?sort_by=name&role=user                  => ?role=user
?gender=male&sort_by=name_desc&role=user => ?gender=male&role=user
?sort_by=name                            => 
?age=24&sort_by=fullname&gender=male     => ?age=24&gender=male
?age=24&sort_by=fullname                 => ?age=24

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