Is there any reason for giving self a default value?

Question

I was browsing through some code, and I noticed a line that caught my attention. The code is similar to the example below

class MyClass:     def __init__(self):         pass      def call_me(self=''):         print(self) 

This looks like any other class that I have seen, however a str is being passed in as default value for self.

If I print out self, it behaves as normal

>>> MyClass().call_me() <__main__.MyClass object at 0x000002A12E7CA908> 

This has been bugging me and I cannot figure out why this would be used. Is there any reason to why a str instance would be passed in as a default value for self?

Answer 1

Not really, it's just an odd way of making it not raise an error when called via the class:

MyClass.call_me() 

works fine since, even though nothing is implicitly passed as with instances, the default value for that argument is provided. If no default was provided, when called, this would of course raise the TypeError for args we all love. As to why he chose an empty string as the value, only he knows.

Bottom line, this is more confusing than it is practical. If you need to do something similar I'd advice a simple staticmethod with a default argument to achieve a similar effect.

That way you don't stump anyone reading your code (like the developer who wrote this did with you ;-):

@staticmethod def call_me(a=''):     print(a) 

If instead you need access to class attributes you could always opt for the classmethod decorator. Both these (class and static decorators) also serve a secondary purpose of making your intent crystal clear to others reading your code.