Python : How to find keys by value in dictionary ?

In this article we will discuss how to find all keys associated with a given single value or multiple values.

Suppose we have a dictionary of words and thier frequency i.e.

# Dictionary of strings and int
dictOfWords = {
    "hello": 56,
    "at" : 23 ,
    "test" : 43,
    "this" : 97,
    "here" : 43,
    "now" : 97
    }

Now we want to get all the keys in dictionary whose value is 43. Like in our case there will two keys who has value 43 i.e.

here
test

Now let’s see how to get the list of keys by given value

Find keys by value in dictionary

As, dict.items() returns an iterable sequence of all key value pairs in dictionary. So, we will iterate over this sequence and for each entry we will check if value is same as given value then we will add the key in a separate list i.e.

'''
Get a list of keys from dictionary which has the given value
'''
def getKeysByValue(dictOfElements, valueToFind):
    listOfKeys = list()
    listOfItems = dictOfElements.items()
    for item  in listOfItems:
        if item[1] == valueToFind:
            listOfKeys.append(item[0])
    return  listOfKeys

Now let’s use this function to get keys by value 43 i.e.

'''
Get list of keys with value 43
'''
listOfKeys = getKeysByValue(dictOfWords, 43)

print("Keys with value equal to 43")
#Iterate over the list of keys
for key  in listOfKeys:
        print(key)

Output:

here
test

Same can be achieved by List Comprehensions i.e.

'''
Get list of keys with value 43 using list comprehension
'''        
listOfKeys = [key  for (key, value) in dictOfWords.items() if value == 43]

Find keys in dictionary by value list

Suppose we want to find all the keys in dictionary whose value matches with any of the value given in list i.e.

[43, 97]

To do that we will iterate over iterable sequence returned by dict.items() and for each entry we will check if its value matches with any entry from the given value list, if yes then we will add that key in a separate list i.e.

'''
Get a list of keys from dictionary which has value that matches with any value in given list of values
'''
def getKeysByValues(dictOfElements, listOfValues):
    listOfKeys = list()
    listOfItems = dictOfElements.items()
    for item  in listOfItems:
        if item[1] in listOfValues:
            listOfKeys.append(item[0])
    return  listOfKeys 

Now lets use this to find all the keys from dictionary whose values is equal to any value from the list i.e.

'''
Get list of keys with any of the given values
'''        
listOfKeys = getKeysByValues(dictOfWords, [43, 97] )

#Iterate over the list of values
for key  in listOfKeys:
    print(key)

Output:

Keys with value equal to any one from the list [43, 97] 
this
here
now
test

Python Dictionary Tutorial - Series:

1. What is a Dictionary in Python & why do we need it?

2. Creating Dictionaries in Python

3. Iterating over dictionaries

4. Check if a key exists in dictionary

5. Check if a value exists in dictionary

6. Get all the keys in Dictionary

7. Get all the Values in a Dictionary

8. Remove a key from Dictionary

9. Add key/value pairs in Dictionary

10. Find keys by value in Dictionary

11. Filter a dictionary by conditions

12. Print dictionary line by line

13. Convert a list to dictionary

14. Sort a Dictionary by key

15. Sort a dictionary by value in descending or ascending order

16. Dictionary: Shallow vs Deep Copy

17. Remove keys while Iterating

18. Get all keys with maximum value

19. Merge two or more dictionaries in python

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Complete example is as follows,

'''
Get a list of keys from dictionary which has the given value
'''
def getKeysByValue(dictOfElements, valueToFind):
    listOfKeys = list()
    listOfItems = dictOfElements.items()
    for item  in listOfItems:
        if item[1] == valueToFind:
            listOfKeys.append(item[0])
    return  listOfKeys  

'''
Get a list of keys from dictionary which has value that matches with any value in given list of values
'''
def getKeysByValues(dictOfElements, listOfValues):
    listOfKeys = list()
    listOfItems = dictOfElements.items()
    for item  in listOfItems:
        if item[1] in listOfValues:
            listOfKeys.append(item[0])
    return  listOfKeys 
    
def main():
    
    # Dictionary of strings and int
    dictOfWords = {
        "hello": 56,
        "at" : 23 ,
        "test" : 43,
        "this" : 97,
        "here" : 43,
        "now" : 97
        }
    
    print("Original Dictionary")
    print(dictOfWords)
    
    '''
    Get list of keys with value 43
    '''
    listOfKeys = getKeysByValue(dictOfWords, 43)
    
    print("Keys with value equal to 43")
    #Iterate over the list of keys
    for key  in listOfKeys:
            print(key)
    
    print("Keys with value equal to 43")
  
    '''
    Get list of keys with value 43 using list comprehension
    '''        
    listOfKeys = [key  for (key, value) in dictOfWords.items() if value == 43]
    
    #Iterate over the list of keys
    for key  in listOfKeys:
            print(key)       
    
    print("Keys with value equal to any one from the list [43, 97] ")
    
    '''
    Get list of keys with any of the given values
    '''        
    listOfKeys = getKeysByValues(dictOfWords, [43, 97] )
    
    #Iterate over the list of values
    for key  in listOfKeys:
        print(key)       
        
            
            
if __name__ == '__main__':
    main()

Output:

Original Dictionary
{'hello': 56, 'at': 23, 'this': 97, 'here': 43, 'test': 43, 'now': 97}
Keys with value equal to 43
here
test
Keys with value equal to 43
here
test
Keys with value equal to any one from the list [43, 97] 
this
here
test
now

 

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