Dictionaries

Dict creation:

Single key-value pair

>>> d = dict(  (('one', 1), )  )         #  using tuple
>>> d = dict(  [('one', 1), ]  )         #  using list   
>>> d = dict( one=1 )                    #  using keyword argument
{'one': 1}

__missing__ method

When accesing non-existing key in a dictionary magic method __missing__ is called with requested key as argument. We can check it like this

>>> class MyDict(dict):
        def __missing__(self, key):
            print(f"You requested key \"{key}\", but it's missing!")

>>> md = MyDict( one=1 )
>>> md
{'one': 1}
>>> md['NoneExistingKey']
You requested key "NoneExistingKey", but it's missing!