Pythonic way to check if a function input is a list or string

Question

I was wondering what the most pythonic way would be to check if a function input is a string or a list. I want the user to be able to enter a list of strings or a string itself.

def example(input):

   for string in input:

       #Do something here.
       print(string)

Obviously this will work in the input is a list of strings but not if the input is a single string. Would the best thing to do here is add type checking in the function itself?

def example(input):

    if isinstance(input,list):
       for string in input:
           print(input)
           #do something with strings
    else:
        print(input)
        #do something with the single string

Thanks.

Use cases for polymorphic functions like this can accept different types are rare, but what you're doing is fine — Chris_Rands, Mar 05 '19 at 10:45
There is nothing wrong with the second approach, I was just wondering if it is the best style to deal with these kind of problems. — Cr1064, Mar 05 '19 at 10:45
@ChristianRobinson Indeed, no harm at all. except one thing I mentioned in my answer below. cheeers! :-) — DirtyBit, Mar 05 '19 at 10:46

ALFA · Answer 1 · 2019-03-05T10:43:37.327

0

Your code is fine. However you mentioned the list should be a list of strings:

if isinstance(some_object, str):
    ...
elif all(isinstance(item, str) for item in some_object): # check iterable for stringness of all items. Will raise TypeError if some_object is not iterable
    ...
else:
    raise TypeError # or something along that line

Check if input is a list/tuple of strings or a single string

edited Mar 05 '19 at 10:43

answered Mar 05 '19 at 10:42

ALFA

1,726
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How is this better than OP's second approach ? – Kunal Mukherjee Mar 05 '19 at 10:43
Forgot to tell his code is fine. However he mentioned the list should be a list of strings. – ALFA Mar 05 '19 at 10:44
Should you add this much checking into code? – Cr1064 Mar 05 '19 at 10:50
This is up to you, if it is necessary for you to check if the list is actually a list of strings yes, definitely. If somehow you're sure it is, it just becomes an almost useless double-check. – ALFA Mar 05 '19 at 10:51

score 0 · Accepted Answer · answered Mar 05 '19 at 10:43

0

The second approach is fine, except that it should do with print(string_) and not print(input), if it matters:

def example(input):
    if isinstance(input,list):
       for string_ in input:
           print(string_)
           #do something with strings
    else:
        print(input)
        #do something with the single string


example(['2','3','4'])
example('HawasKaPujaari')

OUTPUT:

2
3
4
HawasKaPujaari

answered Mar 05 '19 at 10:43

DirtyBit

16,613
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1

Sorry yeah this is correct it was a typo in my original code. As long as this type checking of the list is considered alright style wise I'm happy enough. – Cr1064 Mar 05 '19 at 10:50

Pythonic way to check if a function input is a list or string

2 Answers2