pythonic way to convert variable to list

Question

I have a function whose input argument can either be an element or a list of elements. If this argument is a single element then I put it in a list so I can iterate over the

Answer 1

I like Andrei Vajna's suggestion of hasattr(var,'__iter__'). Note these results from some typical Python types:

>>> hasattr("abc","__iter__")
False
>>> hasattr((0,),"__iter__")
True
>>> hasattr({},"__iter__")
True
>>> hasattr(set(),"__iter__")
True

This has the added advantage of treating a string as a non-iterable - strings are a grey area, as sometimes you want to treat them as an element, other times as a sequence of characters.

Note that in Python 3 the str type does have the __iter__ attribute and this does not work:

>>> hasattr("abc", "__iter__")
True

Answer 2

This seems like a reasonable way to do it. You're wanting to test if the element is a list, and this accomplishes that directly. It gets more complicated if you want to support other 'list-like' data types, too, for example:

isinstance(input, (list, tuple))

or more generally, abstract away the question:

def iterable(obj):
  try:
    len(obj)
    return True
  except TypeError:
    return False

but again, in summary, your method is simple and correct, which sounds good to me!