python structural pattern matching for string containing float

Question

How can I use structural pattern matching for the following use case:

values = ["done 0.0", "done 3.9", "failed system busy"]

for v in values:
   vms = v.split()
   match vms:
       case ['done', float()>0]: # Syntax error
           print("Well done")
       case ['done', float()==0]: # Syntax error
           print("It is okay")
       case ['failed', *rest]:
           print(v)

Please excuse me for the syntax errors, I have written this to demonstrate my thought process.

What could be the right syntax to achieve this pattern matching? Is it even possible?

Answer 1

if...else would be simpler but if you do want pattern matching then you have a number of issues to be resolved. Your string does not contain a float, it contains a string of characters which could be converted to a float. So to test value of a float you have to test that it IS a float in string form and then convert to a float then test. The 'wildcard' character is _ which should be used to capture non-matching elements. The following code does what I think you want and could be the basis for further development. Regex is used to test for the float with a 'guard' expression in the pattern. The Regex would pick up error entries such as "3.x".

import re
values = ["done 0.0", "done 3.9", "failed system busy"]

for v in values:
    vms = v.split()
 
    match vms:
        case ['done', x] if x == '0.0': print(vms, 'It is OK')
        case ['done', x] if re.match(r'\d+.\d+', x) and float(x) > 3.0: print(vms, 'Well done')
        case ['failed', _,_]: print(v)
        case _: print('unknown case')

produces:

['done', '0.0'] It is OK
['done', '3.9'] Well done
failed system busy