Different ways to Iterate / Loop over a Dictionary in Python

In this article we will discuss different ways to iterate over a dictionary

Suppose we have a dictionary with string as key and integers as value i.e.

'''
Creating Dictionaries with string as key and int as value
'''                                  
wordFrequency = {
    "Hello" : 7,
    "hi" : 10,
    "there" : 45,
    "at" : 23,
    "this" : 77
    }

Now let’s see how to iterate over this dictionary using 2 different techniques i.e.

Iterate over the dictionary using for loop over keys | “for in dictionary”

By using for in dictionary, it loops through all the keys in dictionary and for each key select the value and prints it.

'''
Iterate over the dictionary using for loop
'''
for key in wordFrequency:
    value = wordFrequency[key]
    print(key, " :: ", value)

Output:

Hello  ::  7
there  ::  45
at  ::  23
this  ::  77
hi  ::  10

Its not an efficient solution because we are iterating over all the keys in dictionary and for each key we are again searching for its associated value.

Let’s see an efficient method i.e.

Iterate over key value pairs of dictionary using dict.items()

dict.items()

It returns a iterable View object of all key,value elements in the dictionary. Its backed by original dictionary.

Let’s iterate over the list using dict.iter() i.e.

'''
Iterate over the dictionary using items()
'''    
for key , value in wordFrequency.items():
    print(key, " :: ", value)

Output:

Hello  ::  7
there  ::  45
at  ::  23
this  ::  77
hi  ::  10

As, view object is backed by original dictionary, therefore any changes made in dictionary will be reflected in it.
For example,

Take a view object of dictionary i.e.

# Take a dictionary view 
dictView =  wordFrequency.items()

View object is,

dict_items([('this', 77), ('hi', 10), ('Hello', 7), ('there', 45), ('at', 23)])

Now modify the dictionary

wordFrequency["hi"] = 90

Now same view object will also be modified because its backed by original dictionary

dict_items([('this', 77), ('hi', 90), ('Hello', 7), ('there', 45), ('at', 23)])

Complete Series of Python Dictionary tutorials,

1. Introduction to Dictionaries in Python
2. Creating Dictionaries in Python
3. Iterating over dictionaries
4. Check if a key exists in dictionary
5. Get all the keys in Dictionary
6. Get all the Values in a Dictionary
7. Remove a key from Dictionary
8. Add key/value pairs in Dictionary
9. Find keys by value in Dictionary
10. Filter a dictionary by conditions
11. Print dictionary line by line
12. Convert a list to dictionary
13. Sort a Dictionary by key or Value
14. Dictionary: Shallow vs Deep Copy
15. Remove keys while Iterating
16. Get all keys with maximum value
17. Merge two or more dictionaries in python

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Complete example is as follows,

def main():

    '''
    Creating Dictionaries with string as key and int as value
    '''                                  
    wordFrequency = {
        "Hello" : 7,
        "hi" : 10,
        "there" : 45,
        "at" : 23,
        "this" : 77
        }

    '''
    Iterate over the dictionary using for loop
    '''
    for key in wordFrequency:
        value = wordFrequency[key]
        print(key, " :: ", value)
    
    print("**************")    
    
    '''
    Iterate over the dictionary using items()
    '''    
    for key , value in wordFrequency.items():
        print(key, " :: ", value)    

    # Take a dictionary view 
    dictView =  wordFrequency.items()
    
    print("Dictionary View before modification : ", dictView, sep ="\n")
    
    # Modify the dictionary
    wordFrequency["hi"] = 90
    
    print("Dictionary View after modification : ", dictView, sep ="\n")
        
if __name__ == "__main__":
    main()

Output:

there  ::  45
hi  ::  10
this  ::  77
at  ::  23
Hello  ::  7
**************
there  ::  45
hi  ::  10
this  ::  77
at  ::  23
Hello  ::  7
Dictionary View before modification : 
dict_items([('there', 45), ('hi', 10), ('this', 77), ('at', 23), ('Hello', 7)])
Dictionary View after modification : 
dict_items([('there', 45), ('hi', 90), ('this', 77), ('at', 23), ('Hello', 7)])