Python dictionary is an unordered collection of items. Each item of a dictionary has a key-value pair which are separated by a colon(:) and enclosed within curly braces { }.It can be changeable and do not allow duplicate.
Creating a Dictionary
A dictionary may contain any data type and is mutable.Values in a dictionary can be of any data type and can be duplicated, whereas keys can’t be repeated and must be immutable.
Syntax
Accessing Elements on a Dictionary
Dictionary is an unordered data type.Hence, we cannot use the indexing operator to access the values.We will have to use the key to access the associated value.To access data,we can either place the keys inside the square brackets[] or use the get method( ).
Example
Output
Adding and Modifying Entries to a Dictionary
a)Adding Dictionary Entries
TO add a new key value pair or to modify the values of a dictionary , we will use the assignment operator (=).Python evaluates the new entry and checks if there is a similar key in the current dictionary.If there is none,then it appends the key:value pair.If the key alreary exists,then it updates the value of existing key.
Syntax
Example
Output
{‘Name’: ‘leela’, ‘Age’:’21', ‘course’: ‘CSE’}
b)Modifying Dictionary Entries
To modify the current value , use the assignment operator (=) to specify the new value to be associated with the key
Example
Ouput
{‘Name’: ‘Renu’}
Removing or Deleting Elements from a Dictionary
To remove a key:value from a dictionary, we can use the pop( ) method which removes the pair and return the value of the given key.
a) pop( ) method
Used to remove a specified key-value pair from a dictionary and returns the value of the deleted key.
Example
Output
{‘a’: 1, ‘b’: 2, ‘c’: 3}
b)popitem( ) method
Used to remove a random key-value pair from a dictionary.The method does not take an argument and returns the deleted key-value pair.
Output
{‘a’: 1, ‘b’: 2, ‘c’: 3}
c) clear( ) method
Used to remove all the key-value pairs in a dictionary
Example
Output
{}
d) Deleting a Dictionary
The del keyword is used to delete a dictionary.
Example
Output
Python Dictionary Methods
a) Update( )
Updates a dictionary with key-value pairs from another dictionary.
Example
Output
{‘a’: 1, ‘b’: 2, ‘c’: 3, ‘d’: 4,’name’: ’amu’}
b)Item( ) method
Returns list of a dictionary’s key-value pairs.
Example
Output
dict_items([(‘a’, 1), (‘b’, 2), (‘c’, 3), (‘d’, 4)])
c) Value( ) method
Returns a list of dictionary values.
Example
Output
dict_values([1, 2, 3, 4])
d) Keys( ) method
Returns a list of dictionary keys.
Example
Output
dict_keys([‘a’, ‘b’, ‘c’, ‘d’])
e) Setdefault( ) method
Searchers for a given key in a dictionary and returns the value if found.If not, it returns the default value.
Example 1
Output
3
Example 2
Output
None
Dictionary Membership Test
We can use the membership operatoes ‘in’ and ‘not in’ to check whether a specific key exists or not on the dictionary.It is only for dictionary keys, not values.
Example
Output
True
False
True
Using built in functions with dictionary
Python has several built-in functions that can be used with dictionary to perform various tasks.
a) len( )
Returns the number of items on a dictionary.
Example
Output
4
b) sorted( )
Returns a sorted view of dictionary keys but not sort the dicyionary itself.
Example
Output
[‘a’, ‘c’, ‘d’, ‘z’]
c) Creating a dictionary with the dict( ) function
Another way of creating a dictionary is with dict( ),a built-in function.The function allows programmers to create a dictionary out of a list of tuple pairs.Each pair will have two elements that can be used as a key and value.
Example
Output
{‘cat’: ‘kitten’, ‘dog’: ‘puppy’, ‘lion’: ‘cub’}
d) Dictionary Comprehension
Dictionary comprehension is a concise way of creating a new dictionary from a python iterable.It consists of a key-value expression and a for statement enclosed in curly braces { }.
Example
Output
{0: 0, 1: 1, 2: 4, 3: 9, 4: 16, 5: 25, 6: 36, 7: 49, 8: 64, 9: 81}
