Hi There, In this post we’ll see python dictonaries and dictonary methods.

• Python dictionary is an unordered collection of items. While other compound data types have only value as an element, a dictionary has a key: value pair. Dictionaries are optimized to retrieve values when the key is known.

Example dictionary

• Example:

    my_dict = {'name': 'Gopikrishna', 'age': 24, 'single': True, 1 : 'Lucky Number'}
  

• Example dictionary

    >>> student = dict(name="Stark", age=28, male=True)
    >>> student
    {'age': 28, 'male': True, 'name': 'Stark'}
    >>>
  

Accessing dictonary value using key

• Usage:

    >>> student = {'age': 28, 'male': True, 'name': 'Stark'}
    >>> #Reading dict value using key 'name'
    ...
    >>> student['name']
    'Stark'
    >>> print(student.get('phone')) # Will return None if key not presented
    None
  

Dictonary methods

dict.get()

Accessing dictonary value using get() method

• Takes one argument i.e key

• Return value of the corresponding key

    >>> student = {'age': 28, 'male': True, 'name': 'Stark'}
    >>> #Reading dict value using key 'name'
    ...
    >>> student.get('age')
    28
    >>>
  

dict.keys()

Get all keys from a dictonary using keys() method

• Takes no arguments

• Returns list containing keys of the dictonary

    >>> student = {'age': 28, 'male': True, 'name': 'Stark'}
    >>> student.keys()
    ['age', 'male', 'name']
    >>>
  

dict.values()

Get all keys from a dictonary using values() method

• Takes no arguments

• Returns list containing values of the dictonary

    >>> student = {'age': 28, 'male': True, 'name': 'Stark'}
    >>> student.values()
    [28, True, 'Stark']
    >>>	
  

dict.items()

Get all items from a dictonary using items() method

• Takes no arguments

• Returns list of tuple containing keys, values pairs of the dictonary

    >>> student = {'age': 28, 'male': True, 'name': 'Stark'}
    >>> student.values()
    [('age', 28), ('male', True), ('name', 'Stark')]
    >>>	
  

dict.clear()

• Takes no arguments
• Returns None

clear() method Deletes all items from a dict

• Usage:

    >>> student = {'age': 28, 'male': True, 'name': 'Stark'}
    >>> student.clear()
    >>> student
    {}
    >>>
  

dict.copy()

• Takes no arguments
• Returns copy of the dict.

copy() method can create copy of a dict

• Usage:

    >>> student = {'age': 28, 'male': True, 'name': 'Stark'}
    >>> student_copy = student.copy() #Creating student dict copy and storing in student_copy
    >>> student
    {'age': 28, 'male': True, 'name': 'Stark'}
    >>> student_copy
    {'age': 28, 'male': True, 'name': 'Stark'}
    >>>
    >>>
    >>> student == student_copy #Both dicts student and student_copy are same according to values
    True
    >>> student is student_copy #But memory addresses are different
    False
    >>>
  

fromkeys()

• Takes two arguments
• Returns resultent dictonary.

fromkeys() method to give same value for all keys

• Usage:

    >>> my_dict = {}.fromkeys(['name', 'age', 'phone', 'email'], 'unknown')
    >>> my_dict
    {'phone': 'unknown', 'age': 'unknown', 'name': 'unknown', 'email': 'unknown'}
    >>>
  

dict.pop()

• Takes one argument i.e key
• Returns corresponding key, value pair which was removed.

pop() method to delete corresponding key, value pair

• Usage:

    >>> student = {'age': 28, 'male': True, 'name': 'Stark'}
    >>> student
    {'age': 28, 'male': True, 'name': 'Stark'}
    >>> student.pop('male') #Removes key, value pair if key is present and retuns True/False
    True
    >>> student
    {'age': 28, 'name': 'Stark'}
    >>>
  

dict.popitem()

• Takes no arguments
• Returns tuple containing any one random key, value pair which was removed.

popitem() method to delete a random key, value pair

• Usage:

    >>> student = {'age': 28, 'male': True, 'name': 'Stark'}
    >>> student.popitem()
    ('age', 28)
    >>> student
    {'male': True, 'name': 'Stark'}
    >>>
  

dict.update()

• Update keys and values in a dict with another set of key value pair
• Takes one argument i.e dict
• Returns None
• updates the dict by appending given dict.

update() method to delete a random key, value pair

• Usage:

    >>> my_list = {'male': True, 'name': 'Stark'}
    >>> my_list.update({"email": "tony@stark.com", "avenger": True})
    >>> my_list
    {'avenger': True, 'male': True, 'name': 'Stark', 'email': 'tony@stark.com'}
    >>>
  

Iterating Dictionarieswith for loop

• Usage:

    >>> student = {'age': 28, 'male': True, 'name': 'Stark'}
    >>> for key, value in student.items():
    ...     print(key)
    ...     print(value)
    ...
    age
    28
    male
    True
    name
    Stark
    >>>
  

Check exestance of a key in dictonary uisng in keyword

• Usage:

    >>> student = {'age': 28, 'male': True, 'name': 'Stark'}
    >>> 'age' in student #Will return True if key is presented
    True
    >>> 'phone' in student #Will return False if key is not presented
    False
    >>>
  

Check exestance of a value in dictonary

• Usage:

    >>> student = {'age': 28, 'male': True, 'name': 'Stark'}
    >>> 'Stark' in student.values() #Will return True if value is presented
    True
    >>> 'Avengers' in student.values() #Will return False if value is not presented
    False