How to check if len is valid

Question

I have a function

def foo(bar):     #do some things     len(bar) 

If I call

foo(42) 

it throws an exception of

TypeError: object of type 'int' has no len()

How do I check if the entered value can be used with len()?

Answer 1

You can do:

if hasattr(bar, '__len__'):     pass 

Alternatively, you can catch the TypeError.

Answer 2

You can test if the object is Sized:

import collections.abc  if isinstance(bar, collections.abc.Sized): 

The isinstance() test is true if all abstract methods of Sized are implemented; in this case that's just __len__.

Personally, I'd just catch the exception instead:

try:     foo(42) except TypeError:     pass  # oops, no length