Test if a variable is a list or tuple

Question

In python, what\'s the best way to test if a variable contains a list or a tuple? (ie. a collection)

Is isinstance() as evil as suggested here? http://w

Answer 1

In principle, I agree with Ignacio, above, but you can also use type to check if something is a tuple or a list.

>>> a = (1,)
>>> type(a)
(type 'tuple')
>>> a = [1]
>>> type(a)
(type 'list')

Answer 2

if type(x) is list:
    print 'a list'
elif type(x) is tuple:
    print 'a tuple'
else:
    print 'neither a tuple or a list'

Answer 3

Has to be more complex test if you really want to handle just about anything as function argument.

type(a) != type('') and hasattr(a, "__iter__")

Although, usually it's enough to just spell out that a function expects iterable and then check only type(a) != type('').

Also it may happen that for a string you have a simple processing path or you are going to be nice and do a split etc., so you don't want to yell at strings and if someone sends you something weird, just let him have an exception.

Answer 4

On Python 2.8 type(list) is list returns false
I would suggest comparing the type in this horrible way:

if type(a) == type([]) :
  print "variable a is a list"

(well at least on my system, using anaconda on Mac OS X Yosemite)

Answer 5

Not the most elegant, but I do (for Python 3):

if hasattr(instance, '__iter__') and not isinstance(instance, (str, bytes)):
    ...

This allows other iterables (like Django querysets) but excludes strings and bytestrings. I typically use this in functions that accept either a single object ID or a list of object IDs. Sometimes the object IDs can be strings and I don't want to iterate over those character by character. :)

Answer 6

Python uses "Duck typing", i.e. if a variable kwaks like a duck, it must be a duck. In your case, you probably want it to be iterable, or you want to access the item at a certain index. You should just do this: i.e. use the object in for var: or var[idx] inside a try block, and if you get an exception it wasn't a duck...