[Python-ideas] Testing Key-Value Membership In Dictionaries

[Karthick Sankarachary]

Hello Python Ideas,

Currently, to check whether a single key is in a dictionary, we use the "in"
keyword. However, there is no built-in support for checking if a key-value
pair belongs in a dictionary.

Currently, we presuppose that the object being checked has the same type as
that of the key. What if we allowed the "in" operator to accept a tuple that
denotes a (mapped) key-value pair?

Let us consider how that might work using the canonical example given in the
tutorial:

>>> tel = {'jack': 4098, 'sape': 4139}

>>> ('jack', 4098) in tel
True
>>> ('jack', 4000) in tel
False
>>> 'jack' in tel
True

As you can see, the "in" operator would interpret the object as either a key
or a key-value pair depending on the actual types of the object, key and
value. In the key itself happens to be a tuple, then the key-value
membership test would involve a nested tuple, whose first item is a tuple
denoting the key.

Best Regards,
Karthick Sankarachary
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