Python Dictionaries

A Dictionary is a collection of many items. The indices of dictionaries can use different data types. Indices for dictionaries are called keys and values. Key with its associated value is called key:value pair. For example:

dict1 = {"fruit": "apple", "color": "red", "size": "small"}

Accessing Dictionary Items

You can access the dictionary items by referring to the key.

Example:

dict1 = {"fruit": "apple", "color": "red", "size": "small"}
a = dict1["fruit"]
print(a)

Output:

apple

Dictionary have also a get() method that will give the same output.

Example:

dict1 = {"fruit": "apple", "color": "red", "size": "small"}
a = dict1.get("fruit")
print(a)

Output:

apple

Changing Items

You can change the dictionary items by referring to the key.

Example:

dict1 = {"fruit": "apple", "color": "red", "size": "small"}
dict1["fruit"] = "banana"
print(dict1)

Output:

{'fruit': 'banana', 'color': 'red', 'size': 'small'}

Adding Items

You can add a new item in a dictionary using a new key-value pair.

Example:

dict1 = {"fruit": "apple", "color": "red", "size": "small"}
dict1["price"] = "25"
print(dict1)

Output:

{'fruit': 'apple', 'color': 'red', 'size': 'small', 'price': '25'}

Removing Items

You can remove a specified item by using the del statement.

Example:

dict1 = {"fruit": "apple", "color": "red", "size": "small"}
del dict1["size"]
print(dict1)

Output:

{'fruit': 'apple', 'color': 'red'}

You can also use the del statement to delete the entire dictionary.

Example:

dict1 = {"fruit": "apple", "color": "red", "size": "small"}
del dict1
print(dict1)

Output:

Traceback (most recent call last):
  File "C:\Users\Hp\Desktop\py\python.py", line 3, in <module>
    print(dict1)
NameError: name 'dict1' is not defined

Note: Since the total set is deleted an error is raised in the output.

The clear() statement will empty the whole dictionary.

dict1 = {"fruit": "apple", "color": "red", "size": "small"}
dict1.clear()
print(dict1)

{}

Length of a Dictionary

You can define the length of a Dictionary using the len() method.

Example:

dict1 = {"fruit": "apple", "color": "red", "size": "small"}
print(len(dict1))

Output:

3

Checking Whether a Key Exists in a Dictionary

The in and not in operators can check whether a certain key exists in a dictionary.

Example:

dict1 = {"fruit": "apple", "color": "red", "size": "small"}
if "color" in dict1:
  print("Color is red")

Output:

Color is red

Dictionary Methods

There are a set of built-in methods in python which you can use on Dictionary.