Difference between if and if is not None

Question

In writing some XML parsing code, I received the warning:

FutureWarning: The behavior of this method will change in future versions.  Use specific \'len(elem         


        

Answer 1

The behavior of if x is sort of interesting:

In [1]: def truthy(x):
...:     if x:
...:         return 'Truthy!'
...:     else:
...:         return 'Not truthy!'
...:     

In [2]: truthy(True)
Out[2]: 'Truthy!'

In [3]: truthy(False)
Out[3]: 'Not truthy!'

In [4]: truthy(0)
Out[4]: 'Not truthy!'

In [5]: truthy(1)
Out[5]: 'Truthy!'

In [6]: truthy(None)
Out[6]: 'Not truthy!'

In [7]: truthy([])
Out[7]: 'Not truthy!'

In [8]: truthy('')
Out[8]: 'Not truthy!'

So, for example, statements under the conditional if x will not execute if x is 0, None, the empty list, or the empty string. On the other hand if x is not None will only apply when x is exactly None.