Question

I’m trying to overload my functions by passing a single argument which might be a string or a list of strings. Whats the simplest way to end up with a list of strings?

>>> foo
'bar'
>>> bar
['foo', 'bar']

def myfunc(arg):
    listarg = list()
    listarg.extend(arg)
    print listarg

>>> myfunc(bar)
['foo', 'bar']
>>> myfunc(foo)
['b', 'a', 'r']

When I pass foo I want to see ['bar'].

I’ve fooled around with using isinstance(arg, str) or isinstance(arg, unicode) and isinstance(arg, collections.Iterable) but am not thrilled about them since the latter doesn’t work and the former, well can’t I just join to a list or something – I though str would do it but then unicode came along and am now afraid there might be more of them to test against.

Answer 1

In Python 2, str and unicode both derive from basestring.

Alas, in Python 3, there is no such common parent class. Here you shoud test for str and bytes.

---

def myfunc(arg):
    listarg = arg if not isinstance(arg, basestring) else [arg]
    print listarg

>>> myfunc(bar)
['foo', 'bar']
>>> myfunc(foo)
['bar']

>>> print sys.version
2.7.2 (default, Jun 20 2012, 16:23:33)