JS. JS. - 1 year ago 59
Python Question

Way to Treat Python single vals and lists of vals identically?

I'm running into this problem often: I'm creating a function that needs to perform a series of operations on a value, whether that value be a single value or a list of values.

Is there an elegant way to do this:

def convert_val(val):
do a series of things to each value, whether list or single val
return answer or list of answers

rather than what I've been doing?:

def convert_val(val):
if isinstance(val, list):
... do a series of things to each list item,
return a list of answers
... do the same series, just on a single value
return a single answer

One solution would be to create a sub_convert() that would do the series of actions, and then just call it once or iteratively, depending on the type passed in to convert().

Another would be to create a single convert() that would accept the arguments (value, sub_convert()).

Other suggestions that would be more compact, elegant and preferably all in one function?

(I've done several searches here to see if my issue has already been addressed. My appologies if it has.)


Answer Source

If the function makes sense for a single value, as well as for a list, then logically the function's result for a certain list item will not depend on the other items in the list.

For example, a and b should end up identical:

items = [1, 2]
a = convert_val(items)
b = map(convert_val, items)

This example already hints at the solution: the caller knows whether a list or a single value is passed in. When passing a single value, the function can be used as-is. When passing a list, a map invocation is easily added, and makes it clearer what's happening on the side of the caller.

Hence, the function you describe should not exist in the first place!