Shorter, more pythonic way of writing an if statement

Question

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?

Asked By: 32423hjh32423

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Answer 1

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.

Answered By: freiksenet

Answer 2

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.

Answered By: Mark Rushakoff

Answer 3

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?

Answered By: John Lockwood

Answer 4

This is:

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

Answered By: Arkady

Answer 5

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.

Answered By: M. Utku ALTINKAYA

Answer 6

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.

Answered By: user135331

Shorter, more pythonic way of writing an if statement

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