CODEWITHSUNDEEP
pythonif-statement
32423hjh32423
32423hjh32423

Reputation: 3088

Shorter, more pythonic way of writing an if statement

I have this

bc = 'off'

if c.page == 'blog':
    bc = 'on'

print(bc)

Is there a more pythonic (and/or shorter) way of writing this in Python?

Upvotes: 50

Views: 56609

Answers (6)

Mark Rushakoff
Mark Rushakoff

Reputation: 258528

You could use an inline if statement:

>>> cpage = 'blog'
>>> bc = 'on' if cpage == 'blog' else 'off'
>>> bc
'on'
>>> cpage = 'asdf'
>>> bc = 'on' if cpage == 'blog' else 'off'
>>> bc
'off'

There's a bit of a writeup on that feature at this blog, and the relevant PEP is PEP308. The inline if statement was introduced in Python 2.5.

This one is less pythonic, but you can use and/or in this fashion:

>>> cpage = 'asdf'
>>> bc = (cpage == 'blog') and 'on' or 'off'
>>> bc
'off'
>>> cpage = 'blog'
>>> bc = (cpage == 'blog') and 'on' or 'off'
>>> bc
'on'

This one is used more often in lambda statements than on a line by itself, but the form

 A and B or C

is similar to

   if A:
       return B
   else:
       return C

The major caveat to this method (as PEP 308 mentions) is that it returns C when B is false.

Upvotes: 15

M. Utku ALTINKAYA
M. Utku ALTINKAYA

Reputation: 2272

You can use,

a = b if c else d

but if you are using a python version prior to 2.5,

bc = c.page == "blog" and "on" or "off"

can do the trick also.

Upvotes: 3

user135331
user135331

Reputation: 229

Another possibility is to use a dict if you can compute the values outside of the function that accesses them (i.e. the values are static, which also addresses the evaluation issue in scrible's answer's comments).

want_bc = {True: "on", False: "off"}
# ...
bc = want_bc[c.page == "blog"]

I prefer this and/or the tuple indexing solutions under the general rubric of preferring computation to testing.

Upvotes: 4

Arkady
Arkady

Reputation: 15079

This is:

  1. definitely shorter
  2. arguably Pythonic (pre-Python 2.5, which introduced the controversial X if Z else Y syntax)

  3. questionably readable. With those caveats in mind, here it goes:

    bc = ("off","on")[c.page=="blog"]

EDIT: As per request, the generalized form is:

   result = (on_false, on_true)[condition]

Explanation: condition can be anything that evaluates to a Boolean. It is then treated as an integer since it is used to index the tuple: False == 0, True == 1, which then selects the right item from the tuple.

Upvotes: 65

John Lockwood
John Lockwood

Reputation: 3875

Well, not being a python guy please take this with a huge grain of salt, but having written (and, with more difficulty, read) a lot of clever code over the years, I find myself with a strong preference now for readable code. I got the gist of what your original code was doing even though I'm a nobody as a Python guy. To be sure, you could hide it and maybe impress a Python wonk or two, but why?

Upvotes: 33

freiksenet
freiksenet

Reputation: 3679

Shortest one should be:

bc = 'on' if c.page=='blog' else 'off'

Generally this might look a bit confusing, so you should only use it when it is clear what it means. Don't use it for big boolean clauses, since it begins to look ugly fast.

Upvotes: 103

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