What's an alternative to if/elif statements in Python?

Question

My code currently looks something like this:

if option1:
    ...
elif option2:
    ...
elif option3:
    ....

so on so forth. And while I'm not displeased with it, I was wondering if there was a better alternative in python. My script is a console based script where I'm using argparser to fetch for what the user needs.

Tell us more about what you are trying to do; you can use a mapping to model dispatch, for example. — Martijn Pieters, Jul 26 '13 at 12:33
Related reading : http://effbot.org/pyfaq/why-isn-t-there-a-switch-or-case-statement-in-python.htm — Miklos Aubert, Jul 26 '13 at 12:35
if expressions (`optionN`) are constant, you may try dict :) — Grijesh Chauhan, Jul 26 '13 at 12:35
@MartijnPieters I'm using this to determine which arguments the user has selected. — Stupid.Fat.Cat, Jul 26 '13 at 12:36
@Stupid.Fat.Cat not sure, but bools are True and False whereas you have three opetions — Grijesh Chauhan, Jul 26 '13 at 12:38
Dict is a really good idea. [Here's](http://bytebaker.com/2008/11/03/switch-case-statement-in-python/) a link to more information. — Al.Sal, Jul 26 '13 at 12:38
@Stupid.Fat.Cat what I want to suggest for that [check that](http://stackoverflow.com/questions/16625454/how-do-i-use-user-input-to-invoke-a-function-in-python/16625492#16625492) — Grijesh Chauhan, Jul 26 '13 at 12:39
@GrijeshChauhan the options are flags. For example myscript -v -f -d, then option1 (v) would be set as true, f as well and so wil d. Whereas myscript -v -f would have both option 1 and 2 true but 3 would b e false. — Stupid.Fat.Cat, Jul 26 '13 at 12:39
@Stupid.Fat.Cat see every expression covered to some value, I said constant, get an idea from linked question :) — Grijesh Chauhan, Jul 26 '13 at 12:40
If for parsing the command line use a builtin python library e.g. [argparse](http://docs.python.org/3/library/argparse.html), also read their code — mmmmmm, Jul 26 '13 at 12:43
Related : http://stackoverflow.com/questions/17166074/most-efficient-way-of-making-an-if-elif-elif-else-statement-when-the-else-is-don — Ashwini Chaudhary, Jul 26 '13 at 12:44
@Mark I am using it, but after parsing it, I execute the part that the user needs. — Stupid.Fat.Cat, Jul 26 '13 at 12:45

Fredrik Håård · Accepted Answer · 2018-05-07T14:23:35.450

21

If 'option' can contain 'one', 'two', or 'three', you could do

def handle_one():
  do_stuff

def handle_two():
  do_stuff

def handle_three():
  do_stuff


{'one': handle_one, 
 'two': handle_two, 
 'three': handle_three}[option]()

edited May 07 '18 at 14:23

answered Jul 26 '13 at 12:39

Fredrik Håård

2,856
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2

better to add a default, As [I suggested here](http://stackoverflow.com/questions/16625454/how-do-i-use-user-input-to-invoke-a-function-in-python/16625492#16625492) – Grijesh Chauhan Jul 26 '13 at 12:41
Well, that would depend on if a default option is possible/makes sense – Fredrik Håård Jul 26 '13 at 22:58
what if None is passed as input? – Dariusz Krynicki Jul 17 '20 at 07:56
1

@dkrynicki if you need to handle unknowns, you can use .get(option, some_default_function) instead of [option] - it will depend on the use case though, it may hide errors – Fredrik Håård Jul 20 '20 at 09:29

score 7 · Answer 2 · answered Jul 26 '13 at 12:45

I'm guessing you're starting Python scripting with a background somewhere else, where a switch statement would solve your question. As that's not an option in Python, you're looking for another way to do things.

Without context, though, you can't really answer this question very well (there are far too many options).

I'll throw in one (somewhat Pythonic) alternative:

Let's start with an example of where I think you're coming from.

def add_to_x (x):
    if x == 3:
        x += 2
    elif x == 4:
        x += 4
    elif x == 5:
        x += 5
    return x

Here's my alternative:

def add_to_x (x):
    vals = { 3 : 5  ,  4 : 8  ,  5 : 10 }
    return vals[x]

You can also look into lambdas which you can put into the dictionary structure I used.

But again, as said, without context this may not be what you're looking for.

It seems like dictionaries take the cake. Everybody seems to be suggesting that. — Stupid.Fat.Cat, Jul 26 '13 at 12:50

score 3 · Answer 3 · answered Jul 26 '13 at 12:45

This is the first thing that comes to my mind:

Instead of doing this:

if option1:
    a = 1
elif oprtion2:
    a = 2
elif oprtion3:
    a = 3
else:
    a = 0

You can do this:

a = 1 if option1 else 2 if option 2 else 3 if option3 else 0

For more detail, see: PEP 308: Conditional Expressions!

What's an alternative to if/elif statements in Python?

3 Answers3

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