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Python Theory

Dictionary:

  • Dictionaries are used to store data values in key:value pairs.
  • A dictionary is a collection which is unordered, changeable and does not allow duplicates.
  • Dictionary in python is declared inside curly brackets.

    • Declaration:

    dictionary = {'key': 'value1', 'key2': 'value2', 'key3': 'value3'}
    Example
    # Empty Dictionary
    dict = {}

    # Dictionary with integer keys
    dict = {1: 'Apple', 2: 'Graphs'}

    # Dictionary with mixed keys
    dict = {'name': 'skillpundit', 1: [4, 3, 5]}
    Output
    SkillPundit: Python-Dictionary Introduction

    Dictionary vs List

    DictionaryList
    unorderedOrdered
    Accesses via keysAccessed via index
    Collection of key value pairs.Collection of elements.
    Preferred when we have unique key values.Preferred for ordered data
    No Duplicate MembersAllows Duplicate Members
    Changing and Adding Dictionary Elements:

    Add new items or change the value of existing items using an assignment operator.

    Example
    # Changing And Adding Dictionary Elements
    a = {1: 'Apple', 2: 'Graphs', 3: 'Banana'}

    # update value
    a[3] = 'Mango'
    print(a)

    # add item
    a[4] = 'Orange'
    print(a)
    Output
    SkillPundit: Python-Dictionary Introduction

    Operations in Python Dictionary:

    MethodDescription
    clear()Remove all items from the dictionary.
    copy()Returns a copy of the dictionary.
    values()Return all the values inside the dictionary.
    update()Updates the values of the dictionary with specified key value pairs.
    get()Returns the values of the key.
    items()Return a new object of the dictionary's items in (key, value) format.
    keys()Returns all the keys inside dictionary.
    pop()Pop the value with the specified key.
    popitem()The popitem() method removes the last inserted item in dictionary.
    Example
    #Removing Elements From a Dictionary
    #Create Dictionary
    a = {1:1,2:4,3:9,4:16,5:25}

    #Remove a Particular Item
    #Output: 16
    print(a.pop(4))
    print(a)

    #Remove an arbitrary Item
    #Output: (5,25)
    print(a.popitem())
    print(a)

    #Remove all items
    a.clear() #Output: {}
    print(a)

    #Delete the Dictionary
    del a #Throws Error
    print(a)
    Output
    SkillPundit: Python-Dictionary Methods
    Example
    #Dictionary Methods
    #Create a Dictionary
    a = {1:1 ,2:4 ,3:9 ,4:16 ,5:25}

    #List of all the Values in the dictionary
    print(a.values())

    #items()
    print(a.items())

    #get()
    print(a.get(3))

    #keys
    print(a.keys())

    #setdefault
    print(a.setdefault(5))
    Output
    SkillPundit: Python-Dictionary Methods

    Loops through Dictionary:

    Loops through dictionary by using a for loop

    Example
    #Loops Through Dictionary
    #Create a Dictionary
    a = {1:1, 2:4, 3:9}

    for X in a:
    print(a[X])
    for X,Y in a.items():
    print(X,Y)
    Output
    SkillPundit: Python-Dictionary Loops