More pythonic way to write this?

Question

I have this code here:

import re
def get_attr(str, attr):
    m = re.search(attr + r'=(\w+)', str)
    return None if not m else m.group(1)

str = 'type=greeting hello=world'

print get_attr(str, 'type')   # greeting    
print get_attr(str, 'hello')  # world
print get_attr(str, 'attr')   # None

Which works, but I am not particularly fond of this line:

return None if not m else m.group(1)

In my opinion this would look cleaner if we could use a ternary operator:

return (m ? m.group(1) : None)

But that of course isn't there. What do you suggest?

`None if not m else m.group(1)` **is** the Python equivalent to `m ? m.group(1) : None`! — , Sep 29 '10 at 17:02
@delnan I know. It just doesn't strike as particularly readable to me; maybe I am too used to the "regular" ternary operator. That's why I am asking this question. — NullUserException, Sep 29 '10 at 17:03
What makes `?` and `:` more readable than `if .. else` ? You can actually read that line out loud! — Jochen Ritzel, Sep 29 '10 at 17:14
It seems like the only advantage in your preferred ternary syntax is order, so why not just use that order in python, i.e. return m.group(1) if m else None? Sure seems easier to follow to me than c-style ternary syntax. Perhaps you were thinking the first return value would get evaluated before the conditional? — Jeffrey Harris, Sep 29 '10 at 18:33

score 10 · Accepted Answer · answered Sep 29 '10 at 16:59

Python has a ternary operator. You're using it. It's just in the X if Y else Z form.

That said, I'm prone to writing these things out. Fitting things on one line isn't so great if you sacrifice clarity.

def get_attr(str, attr):
    m = re.search(attr + r'=(\w+)', str)
    if m:
        return m.group(1)

    return None

score 4 · Answer 2 · answered Sep 29 '10 at 17:04

4

Another option is to use:

return m.group(1) if m else m

It's explicit, and you don't have to do any logic puzzles to understand it :)

answered Sep 29 '10 at 17:04

unutbu

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How is that more explicit than return None? Who knows what `m` is there? What if m is actually '' or 0 or some custom class that evaluates to False – Falmarri Sep 29 '10 at 19:01

score 3 · Answer 3 · answered Sep 29 '10 at 16:58

3

return m and m.group(1)

would be one Pythonic way to do it.

If m is None (or something else that evaluates "falsely"), it returns m, but if m is "true-ish", then it returns m.group(1).

answered Sep 29 '10 at 16:58

Mark Rushakoff

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I feel like this is trying to be too hard to be clever. – Daenyth Sep 29 '10 at 17:00
Actually, if expressions have superseded the clever use of the fact that boolean operators return their operands. – Sep 29 '10 at 17:01
2

Agreed. It works, but it kind of feels like an abuse of the `and` operator. Oddly, I don't feel the same way about the `or` operator (e.g. `return x or 'NO VALUE'`) – Chris B. Sep 29 '10 at 17:03
To me it looks much more "perlish" than pythonic. (i.e. too much idiomatic) – Boris Gorelik Nov 24 '11 at 17:42

score 2 · Answer 4 · answered Sep 29 '10 at 17:01

2

What you have there is python's conditional operator. IMO it's perfectly pythonic as-is and needs no change. Remember, explicit is better than implicit. What you have now is readable and instantly understandable.

answered Sep 29 '10 at 17:01

Daenyth

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More pythonic way to write this?

4 Answers4