Find keyword in snake_case texts

I have a problem where I need to find if a word(for example "output") is present in a snake_case word.

Which means the regex must be capable of matching all of the following situations-

• output
• output_of_my_program
• my_output_from_program
• program_output

i.e. output, output_, output, and _output need to be matched

currently I have three individual regex patterns to cover all the cases, which are-

• "^output[^a-z]_?"
• "_output_"
• "_output$"

I however have tried to combine the three into one, which is [a-z]*_?[^a-z]output_?[a-z]* but this fails for certain cases. Is it possible to combine the three patterns into one in this case?

Edit:The other keywords I am interested in are "in", "input", "out" and the challenge is to avoid matches with words such as "introspection" and other cases such as "my_programoutput"

>Solution :

You don’t include it in your test cases, but I assume part of the intent is to explicitly not match a string like my_floutputs_from_program. You could do this with a tricky regex, but I’d just use split and in:

for s in (
    'output', 
    'output_of_my_program', 
    'my_output_from_program', 
    'program_output', 
    'input', 
    'my_floutputs_from_program'
):
    print(f"{s}: {'output' in s.split('_')}")

output: True
output_of_my_program: True
my_output_from_program: True
program_output: True
input: False
my_floutputs_from_program: False