Question

I’ve found the following open source code in Python:

class Wait:

  timeout = 9

  def __init__(self, timeout=None):

    if timeout is not None:
        self.timeout = timeout
    ...

I’m trying to understand if there are advantages of the code above vs using default argument’s value:

class Wait:

   def __init__(self, timeout=9):
     ...

Answer 1

It’s possible to change the default value this way:

Wait.timeout = 20

Will mean that, if unset, the default will be 20.

E.g:

>>> class Wait:
...     timeout = 9
...     def __init__(self, timeout=None):
...         if timeout is not None:
...             self.timeout = timeout
... 
>>> a = Wait()
>>> b = Wait(9)
>>> a.timeout
9
>>> b.timeout
9
>>> Wait.timeout = 20
>>> a.timeout
20
>>> b.timeout
9

This utilises the fact that Python looks for class attributes if it doesn’t find an instance attribute.