Efficient if-elif for changing multiple variables

Question

I have several variables, some of which I need to change on a certain condition.

test = 'foo'
a, b, c = None, None, None
if test == 'foo':
    a = 1
elif test == 'bar':
    b = 2
else:
    c = 3

I'd like to use the dict approach described here, but how can I modify it to change multiple variables? I want it to work like this:

options = {'foo': ('a',1), 'bar': ('b',2)}
reassign_variables(options,test, ('c',3))

Or can this not be done without creating a function and hard-coding all of the conditions in separately?

what do you want options to be after your reassign_variables() — niklas, Mar 20 '17 at 16:09
Why is `'c'` not in the `options` dictionary? It could have a key of (for example) `'default'.` — cdarke, Mar 20 '17 at 16:09
@niklas I want them to remain the same, but I want r_v() to change variables specified in options — lotrus28, Mar 20 '17 at 16:10
Not sure what you want, but [`dict.update`](https://docs.python.org/3/library/stdtypes.html#dict.update) might be what you're looking for. — a_guest, Mar 20 '17 at 16:12

score 2 · Accepted Answer · answered Mar 20 '17 at 16:15

This will change variables in the module's global namespace

>>> options = {'foo': ('a',1), 'bar': ('b',2)}
>>> 
>>> def reassign_variables(options, test, default):
...     var, val = options.get(test, default)
...     globals()[var] = val
... 
>>> 
>>> a, b, c = None, None, None
>>> reassign_variables(options, "foo", ('c',3))
>>> a,b,c
(1, None, None)
>>> reassign_variables(options, "baz", ('c',3))
>>> a,b,c
(1, None, 3)
>>>

score 0 · Answer 2 · answered Mar 20 '17 at 16:12

0

Use the dict.update method like so, if I get you right:

test = 'foo'
options.update({test:('a',12)})

answered Mar 20 '17 at 16:12

niklas

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score 0 · Answer 3 · answered Mar 20 '17 at 16:27

0

you can resign the values back to variables

a,b,c = None, None, None
options = {'foo': (1,b,c), 'bar': (a,1,c)}
default = (a,b,1)
test = 'foo'
a,b,c = options.get(test,default)

answered Mar 20 '17 at 16:27

galaxyan

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This is not scalable, as you would have to modify N-1 tuples every time and adding an extra one – Adirio Mar 20 '17 at 16:32

score -1 · Answer 4 · edited May 23 '17 at 11:55

-1

According to this, you can access variables by name using globals(). Applying this method to the problem you are trying to solve, all you have to do is use your default value in the call to options.get

test = 'foo'
options = {'foo': ('a', 1), 'bar': ('b', 2)}
default = ('c', 3)
var_name, var_value = options.get(test, default)
globals()[var_name] = var_value

If the variables are members of an object, you can use setattr as explained here.

edited May 23 '17 at 11:55

Community

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answered Mar 20 '17 at 16:29

Pablo Gutierrez Marques

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It works, but the answer given by @tdelaney has better handling of the default case and gives it as a function as the OP suggested – Adirio Mar 20 '17 at 16:31
This provides a two-line solution that does not require the creation of a function – Pablo Gutierrez Marques Mar 20 '17 at 16:37
The 4 lines you had when I first commented weren't as elegant. (Edits are stored Pablo) Your current 2 lines are the same that in the function, so this answer now provides nothing new except from not using a function. The OP gave a function template the other answer complies with, while yours doesn't. – Adirio Mar 21 '17 at 13:44

Efficient if-elif for changing multiple variables

4 Answers4