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

Question

I’ve a method that I want to be able to accept either a single string (a path, but not necessarily one that exists on the machine running the code) or a list/tuple of strings.

Given that strings act as lists of characters, how can I tell which kind the method has received?

I’d like to be able to accept either standard or unicode strings for a single entry, and either lists or tuples for multiple, so isinstance doesn’t seem to be the answer unless I’m missing a clever trick with it (like taking advantage of common ancestor classes?).

Python version is 2.5

Asked By: mavnn

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Source

Answer 1

Have you considered varargs syntax? I’m not really sure if this is what you’re asking, but would something like this question be along your lines?

Answered By: David Berger

Answer 2

You can check if a variable is a string or unicode string with

Python 3:

    isinstance(some_object, str)

Python 2:

    isinstance(some_object, basestring)

This will return True for both strings and unicode strings

As you are using python 2.5, you could do something like this:

if isinstance(some_object, basestring):
    ...
elif all(isinstance(item, basestring) 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

Stringness is probably not a word, but I hope you get the idea

Answered By: Steef

Answer 3

Check the type with isinstance(arg, basestring)

Answered By: Ants Aasma

Answer 4

Type checking:

def func(arg):
    if not isinstance(arg, (list, tuple)):
        arg = [arg]
    # process

func('abc')
func(['abc', '123'])

Varargs:

def func(*arg):
    # process

func('abc')
func('abc', '123')
func(*['abc', '123'])

Answered By: FogleBird

Answer 5

isinstance is an option:

In [2]: isinstance("a", str)
Out[2]: True

In [3]: isinstance([], str)
Out[3]: False

In [4]: isinstance([], list)
Out[4]: True

In [5]: isinstance("", list)
Out[5]: False

Answered By: besen

Answer 6

As I like to keep things simple, here is the shortest form that is compatible with both 2.x and 3.x:

# trick for py2/3 compatibility
if 'basestring' not in globals():
   basestring = str

v = "xx"

if isinstance(v, basestring):
   print("is string")

Answered By: sorin

Answer 7

Can’t you do:

(i == list (i) or i == tuple (i))

It would reply if the input is tuple or list. The only issue is that it doesn’t work properly with a tuple holding only one variable.

Answered By: DragonZeith

Answer 8

>>> type('abc') is str
True
>>> type(['abc']) is str
False

This code is compatible with Python 2 and 3

Answered By: Vlad Bezden

Answer 9

I’m surprised no one gave an answer with duck typing, but gave unclear or highly type-dependent or version-dependent answers. Also, the accepted answer unfortunately has separate code for Python 2 and 3. Python uses and encourages duck typing, so (one line more than sorin’s "shortest form" which is not duck typing) I instead recommend:

def is_str(v):
    return hasattr(v, 'lower')

…and whatever other attributes you want to use (remember the quotes). That way, client code using your software can send whatever kind of string they want as long as it has the interface your software requires. Duck typing is more useful in this way for other types, but it is generally the best way.

Or you could also do this (or generally check for AttributeError and take some other action):

def is_str(v):
    try:
        vL = v.lower()
    except AttributeError:
        return False
    return True

Answered By: Poikilos

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

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