Python Dictionaries

Dictionary is an unordered collection of key-value pairs. "dict" is a built-in Python class that represents a dictionary object.

The contents of a dict can be written as a series of key:value pairs within braces { } e.g. dict = {key1:value1, key2:value2, ... }.

The "empty dict" is just an empty pair of curly braces {}.

my_dict = {}
my_dict['a'] = 'alpha'
my_dict['g'] = 'gamma'
my_dict['o'] = 'omega'

print(my_dict)

{'a': 'alpha', 'g': 'gamma', 'o': 'omega'}

The keys will appear in an arbitrary order. The methods dict.keys() and dict.values() return lists of the keys or values.

my_dict.keys()

dict_keys(['a', 'g', 'o'])

print(my_dict['a'])
print(my_dict['g'])
print(my_dict['o'])

alpha
gamma
omega

Add a new key value pair to dictionary

my_dict['b'] = 'beta'
my_dict

{'a': 'alpha', 'g': 'gamma', 'o': 'omega', 'b': 'beta'}

Remove value from dictionary using its key

del my_dict['a']
my_dict

{'g': 'gamma', 'o': 'omega', 'b': 'beta'}

You can also use 'pop' to remove the value from dictionary

Difference between del and pop()

• pop() method is a built-in Python method that can be used to remove an item from a dictionary by specifying its key, it also returns the removed value.

value = my_dict.pop('o')
value

'omega'

Removing an item from a dictionary with a non-existent key, gives a KeyError exception

del my_dict['invalidkey']

---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-7-df2b2ffef6fa> in <module>
----> 1 del my_dict['invalidkey']

KeyError: 'invalidkey'

value = my_dict.pop('invalidkey')

my_dict