Python Notes
March 2021


In Python, every time you call a function or method such as my_function() or my_class.my_method() the interpreter will replace the ( with .__call__(

>>> def my_function(x):
>>>    return x+1

>>> my_function.__call__(2)
class Prefixer:
    def __init__(self, prefix):
       self.prefix = prefix
    def __call__(self, message):
       return self.prefix + message

Then use prefixer like this:

>>> simonsays = Prefixer("Simon says: ")
>>> simonsays("jump up high!")
'Simon says: jump up high!'

Every time you call a function or method, you’re really just calling a built in __call__ method.

There should be one, and preferably only one, obvious way to do something

It’s in the ‘zen of Python’, which is a set of guidelines that help make design decisions. It’s a choice that Python made, and other languages do it differently.

There are different levels to languages and this applies more to the idiom level than the design pattern level. It applies even less at the architectural level where there can be several equally good ways of organizing business logic and data representations.

Perl has the “TMTOWTDI” (tim towtdi) principle - “There’s More Than One Way To Do It”. Perl’s philosophy is to give users more than one way to do something.