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      Dictionaries

      Python Tutorial

      This Python tutorial has been written for the beginners to help them understand the basic to advanced concepts of Python Programming Language. After completing this tutorial, you will find yourself at a great level of expertise in Python, from where you can take yourself to the next levels to become a world class Software Engineer.

      Dictionaries

      Dictionary is one of the built-in data types in Python. Python's dictionary is example of mapping type. A mapping object 'maps' value of one object with another.
      In a language dictionary we have pairs of word and corresponding meaning. Two parts of pair are key (word) and value (meaning). Similarly, Python dictionary is also a collection of key:value pairs. The pairs are separated by comma and put inside curly brackets {}.
      To establish mapping between key and value, the colon ':' symbol is put between the two.
      Given below are some examples of Python dictionary objects
      capitals = {"Maharashtra":"Mumbai", "Gujarat":"Gandhinagar", "Telangana":"Hyderabad", "Karnataka":"Bengaluru"}
      numbers = {10:"Ten", 20:"Twenty", 30:"Thirty",40:"Forty"}
      marks = {"Savita":67, "Imtiaz":88, "Laxman":91, "David":49}

      Example 1

      Only a number, string or tuple can be used as key. All of them are immutable. You can use an object of any type as the value. Hence following definitions of dictionary are also valid
      d1 = {"Fruit":["Mango","Banana"], "Flower":["Rose", "Lotus"]}
      d2 = {('India, USA'):'Countries', ('New Delhi', 'New York'):'Capitals'}
      print (d1)
      print (d2)
      It will produce the following output
      {'Fruit': ['Mango', 'Banana'], 'Flower': ['Rose', 'Lotus']}
      {'India, USA': 'Countries', ('New Delhi', 'New York'): 'Capitals'}

      Example 2

      Python doesn't accept mutable objects such as list as key, and raises TypeError.
      d1 = {["Mango","Banana"]:"Fruit", "Flower":["Rose", "Lotus"]}
      print (d1)
      It will raise a TypeError
      Traceback (most recent call last):
         File "C:\Users\Sairam\PycharmProjects\pythonProject\main.py", line 8, in <module>
      d1 = {["Mango","Banana"]:"Fruit", "Flower":["Rose", "Lotus"]}
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      TypeError: unhashable type: 'list'

      Example 3

      You can assign a value to more than one keys in a dictionary, but a key cannot appear more than once in a dictionary.
      d1 = {"Banana":"Fruit", "Rose":"Flower", "Lotus":"Flower", "Mango":"Fruit"}
      d2 = {"Fruit":"Banana","Flower":"Rose", "Fruit":"Mango", "Flower":"Lotus"}
      print (d1)
      print (d2)
      It will produce the following output
      {'Banana': 'Fruit', 'Rose': 'Flower', 'Lotus': 'Flower', 'Mango': 'Fruit'}
      {'Fruit': 'Mango', 'Flower': 'Lotus'}

      Python Dictionary Operators

      In Python, following operators are defined to be used with dictionary operands. In the example, the following dictionary objects are used.
      d1 = {'a': 2, 'b': 4, 'c': 30}
      d2 = {'a1': 20, 'b1': 40, 'c1': 60}
      Operator
      Description
      Example
      dict[key]
      Extract/assign the value mapped with key
      print (d1['b']) retrieves 4
      d1['b'] = 'Z' assigns new value to key 'b'
      dict1|dict2
      Union of two dictionary objects, retuning new object
      d3=d1|d2 ; print (d3)
      {'a': 2, 'b': 4, 'c': 30, 'a1': 20, 'b1': 40, 'c1': 60}
      dict1|=dict2
      Augmented dictionary union operator
      d1|=d2; print (d1)
      {'a': 2, 'b': 4, 'c': 30, 'a1': 20, 'b1': 40, 'c1': 60}

      Practice with Online Editor

      Note: This Python online Editor is a Python interpreter written in Rust, RustPython may not fully support all Python standard libraries and third-party libraries yet.
      Remember to save code(Ctrl + S Or Command + S) before run it.