[Python-ideas] Ternary operators in list comprehensions

[Rob Cliffe]

Putting it another way, your example doesn't make sense.  How would you 
parenthesise it to make it clearer?

     [ (x for x  in a if x & 1) else 'even']     You have an "else" 
without an "if".

     [ x for x  in (a if x & 1 else 'even')]     Using x before it has 
been defined, at least in this line of code.

     [ (x for x  in a) if x & 1 else 'even']     Ditto

Other variants may be possible.  Whereas Jelle's correct version can be 
written as

     [(x if x & 1 else 'even') for x in a]        [1, 'even', 3]

Rob Cliffe


On 05/10/2017 16:44, Jelle Zijlstra wrote:
> [x if x & 1 else 'even' for x in a]
>
> An `if` at the end of the comprehension means a condition on whether 
> to include the value.
>
> Also, this question would have been better asked on python-list.
>
> 2017-10-05 8:40 GMT-07:00 Jason H <jhihn at gmxcom <mailto:jhihn at gmx.com>>:
>
>     >>> a = [1,2,3]
>     >>> [ x for x  in a if x & 1]
>     [1, 3]
>     >>> [ x for x  in a if x & 1 else 'even']
>       File "<stdin>", line 1
>         [ x for x  in a if x & 1 else 'even']
>                                     ^
>     SyntaxError: invalid syntax
>
>     I expected [1, 'even', 3]
>
>     I would expect that the if expression would be able to provide
>     alternative values through else.
>
>     The work around blows it out to:
>     l = []
>     for x in a:
>       if x&1:
>         l.append(x)
>       else:
>         l.append('even')
>
>
>     Unless there is a better way?
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