Python Dictionaries

Introduction to Dictionaries in Python:

A dictionary in Python Programming Language is a container for a set of key-value pairs. The key-value pairs stored in a Python Dictionary maintain the insertion order.
The other programming language equivalents of a Python dictionary include maps of C++ Standard Library and the associative arrays of the Perl.

Key	Value
USA	Washington D.C.
UK	London
Japan	Tokyo
France	Paris

The dictionary implementation in Python is provided through the class dict.
The keys present in a Python dictionary are unique. There will not be any duplicate keys in a Python dictionary. The collection of key space in a Python dictionary is a set i.e., no two keys are same in a set.
The keys of a Python dictionary should be of immutable types.
A string literal, a numeric value can all be stored as a key in a Python dictionary. A Python tuple as well can be stored as a key in a Python dictionary for the reason being a string, a numeric value, a tuple are all immutable types.
However, a python list cannot be stored as a key in a Python dictionary, as a list is a mutable object.

Construction of a Python Dictionary:

Using braces { }

Dictionary objects in python are crated by placing key-value pairs inside a pair of braces.

Creates an empty dictionary.

dict(keyword-argument-list)

Creates a python dictionary as specified in the keyword-argument-list.

Creates a python dictionary from a mapping object or from another dictionary.

Creates a python dictionary from an iterable object.

Methods of the Python Dictionary class:

dict[dict_key_in]

Retrieves the value associated with dict_key_in parameter, otherwise called a dictionary lookup.

get(dict_key[,default_value])

Returns the value associated with a key in the python dictionary object.

del dict[dict_key_in]

Deletes a key-value pair as identified by the key.

The clear() method removes all the items from the dictionary.

Returns a shallow copy of the Python dictionary object.

get(dict_key[,default_value])

Returns the value associated with a key in the Python dictionary object.

Removes an arbitrary item from a Python Dictionary object.

Built in Functions available for a Python Dictionary object:

Returns the number of items stored in a python dictionary object.

Determines whether a given key is present in the Python dictionary.

key not in dict

Determines whether a given key is not present in the Python dictionary.

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