using else in inline conditional python

Question

I know I can do this:

z = a if switch == 1 else z = b

but what if I want z=a if switch=1, z=b if switch=2, and z=c if switch=3? Is there a python valid way to write this as a single line?

something like:

z = a if switch == 1 else z = b if switch == 2 else z = c

Thanks, just learning Python now (obviously).

FWIW, z = a if switch == 1 else z = b is not valid since the assignment z = b is a statement, not an expression. I think you mean z = a if switch == 1 else b :-) — mgilson
– mgilson, Commented Aug 9, 2015 at 20:02
This is a recipe for confusing code, which is not Pythonic. If you're got something more complicated than a single ternary operator can handle, don't use ternary operators. — jwilner
– jwilner, Commented Aug 9, 2015 at 20:08
Or, in the case of python, a "conditional expression" which is the equivalent to a ternary operator in other languages :-). — mgilson
– mgilson, Commented Aug 9, 2015 at 20:22
mgilson, thank you, yes indeed - sorry to be so new to this all! jwilner - I don't disagree, this is more a question of what is possible, not what is recommended. ;) — Sindyr
– Sindyr, Commented Aug 9, 2015 at 21:13

Patrick Maupin · Accepted Answer · 2015-08-09 19:58:50Z

5

Like this:

z = a if switch == 1 else (b if switch == 2 else c)

And you can keep going, but you didn't say what to use after c if it wasn't 3...

answered Aug 9, 2015 at 19:58

Patrick Maupin

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5 Comments

NightShadeQueen Over a year ago

You technically don't need the parens, but personally I think it's a lot more readable with :P

Sindyr Over a year ago

Oh wow, I actually imagined that this was not doable - it's so cool to see that! Would you just keep nesting parens with more options? z = a if switch == 1 else (b if switch == 2 else (c if switch == 3 else d)) for example?

Patrick Maupin Over a year ago

@SindyR Yes, but at some point, you might want to rethink your strategy, and use a dict lookup or something :)

Sindyr Over a year ago

I am sure, this is likely not Pythonic at all, but I was curious to see what was possible. :)

Patrick Maupin Over a year ago

@NightShadeQueen True. Interestingly, z = a if b else c if d else e is accepted by the compiler even though it's ambiguous (you have to know that it is interpreted the way I wrote it instead of z = (a if b else c) if d else e -- but z = a if b if c else d else e is a syntax error even though it is unambiguous.

mgilson · Accepted Answer · 2015-08-09 20:00:13Z

1

if a, b, c, ... are static, then you might as well just use a dict:

lookup = {1: a, 2: b, 3: c}
z = lookup[switch]

It'd probably be most efficient if you could generate dict only once and reuse it every time. Also note that since switch seems to be sequential integers starting at 1, you could also use a list (or tuple):

lookup = (a, b, c)
z = lookup[switch - 1]

answered Aug 9, 2015 at 20:00

mgilson

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1 Comment

Sindyr Over a year ago

thanks, I'll keep this in mind - I am sure that a dict in this case may be more Pythonic, but I like knowing what functions in Python even when idiom doesn't recommend it. ;)

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