Single string or list of strings in a method [duplicate]

Answer 1

Simple test the type of the parameter:

def test(a,b):
    x = a if isinstance(a, list) else [a]
    x += b if isinstance(b, list) else [b]
    return x

Answer 2

A little tweak to pod2metra's answer enables the function to handle all levels of annidation:

>>> def b(*args):
...     x=[]
...     for i in args:
...             if '__iter__' in dir(i):
...                     x += b(*i)
...             else:
...                     x.append(i)
...     return x
... 
>>> b(1, (2, (3, 4)))
[1, 2, 3, 4]

Instead with the function 'a' you had:

>>> a(1, (2, (3, 4)))
[1, 2, (3, 4)]

I know it was not in the intentions of the original question, but maybe this generalization can be useful.

Answer 3

From The Zen of Python:

Explicit is better than implicit.

In my opinion, your first example is explicit. It takes two values and processes them in well-understood ways. Although it "feels" a little strange to new Python programmers, it behaves just like expect. list.extend accepts lists, so it treats strings like a list of chars.

Your proposal alters the semantics of list.extend to be equivalent to list.append, but only when dealing with strings. That would be a real surprise to someone who wants your function to treat your strings as lists of chars and who would then have to call it like test(x,list('test')).

You can do what you're asking, but please don't. :-)

Answer 4

Use this

def test( x, *args ):

Now you can do

test( x, 'one' )

and

test( x, 'one', 'two' )

and

test( x, *['one', 'two',] )

Answer 5

I'm sorry to say it but this really is one of the few cases where using isinstance() makes sense. However one of the other answers that suggests testing for list is doing it backwards: str (and for Python 2.x unicode) are the anomalous types so those are the ones you test for:

def test(a,b):
    x = []
    if isinstance(b, str): b = [b]
    x.extend(a)
    x.extend(b)
    return x

or for Python 2.x test isinstance(b, basestring).

Answer 6

Hm, may this is easy way:

>>> def a(*args):
...     x=[]
...     for i in args:
...             if '__iter__' in dir(i):
...                     x+=list(i)
...             else:
...                     x.append(i)
...     return x
... 
>>> a(1,2,3,4)
[1, 2, 3, 4]
>>> a(1,2,[3,4])
[1, 2, 3, 4]
>>> a(1,2,[3,4],'123')
[1, 2, 3, 4, '123']
>>> a(1,2,[3,4],'123', 1231, (1, 2, 3, 4))
[1, 2, 3, 4, '123', 1231, 1, 2, 3, 4]