How to remove a key value pair from a dictionary in Python

Key takeaways

  • In Python, dictionaries store data as key-value pairs, each key identifying a unique value.

  • Removing key-value pairs is important for handling data and keeping dictionaries up-to-date.

  • There are several methods for removing keys from dictionaries:

    • The del keyword: Directly removes a key-value pair by referencing the key

    • The popitem() method: Removes the last inserted key-value pair

    • The pop(key[, default]) method: Removes a specific key-value pair and optionally provides a default value if the key doesn’t exist

A dictionary contains a collection of indexes and values (indexes are also called keys). Each key is associated with a single value which helps in efficient retrieval. The association of a key and a value is called a key-value pair or an item. 

new_dict = {'Color': 'Yellow', 'Type': 'Sun flower', 'Quantity': 50}

Here, 'Color', 'Type', and 'Quantity' are keys, and 'Yellow', Sun flower, and 50 are their corresponding values.

Where are dictionaries used?

Dictionaries are used in various scenarios as listed below:

  • Many NoSQL databases, like Redis and MongoDB, store data as key-value pairs.

  • Web APIs commonly use key-value pairs to send data between servers and clients.

  • key-value pairs are used in configuration files to set parameters and options for applications.

Python provides support for the dictionary data structure. Understanding how to remove key-value pairs from a Python dictionary is necessary for removing obsolete or incorrect key-value pairs. There are several ways to remove a key-value pair from a dictionary as listed below:

There are also ways to remove multiple or all keys from a dictionary:

  • We can remove multiple keys from a dictionary using the pop() method.

  • We can delete all Keys from a Dictionary using the del keyword.

Method 1: Remove a key-value pair from a dictionary using the del keyword

The del keyword deletes a key-value pair from a dictionary. We simply access the value that needs to be deleted and use the following syntax:

del dict[key]

If the key-value pair does not exist, a KeyError exception is thrown.

# declare a dictionary
dict1 = {1: "one", 2: "two", 3: "three", 4: "four"}
print("Original Dictionary: ", dict1)
# using del and giving the key as index
del dict1[1]
print("Dictionary after del: ", dict1)
# using del and giving the key as index
del dict1[3]
print("Dictionary after del: ", dict1)

Method 2: Remove a key-value pair from a dictionary using the popitem() method

The built-in popitem() method deletes the last key-value pair in a dictionary. We cannot specify the element that needs to be deleted. The function takes no arguments.

dict.popitem()

A KeyError exception is thrown if the dictionary is empty. Otherwise, the key-value pair is returned as a tuple.

# declare a dictionary
dict1 = {1: "one", 2: "two", 3: "three", 4: "four"}
print("Original Dictionary: ", dict1)
# using popitem()
valDel = dict1.popitem()
print("Dictionary after using popitem(): ", dict1)
print("The key:value pair that was removed is: ", valDel)
# using popitem()
valDel = dict1.popitem()
print("Dictionary after using popitem(): ", dict1)
print("The key:value pair that was removed is: ", valDel)

Method 3: Remove a key-value pair from a dictionary using the pop() method

The built-in pop() method deletes a specific key-value pair from a dictionary.

dict.pop(key[, default])

The function takes two arguments:

  1. key: The key of the value that needs to be deleted

  2. default: An optional argument (the default value is returned if the key does not exist in the dictionary)

If the key does not exist and the default argument is not given, a KeyError exception is returned. This can be avoided using the second argument.

Otherwise, if the key exists, the value of the element removed is returned.

# declare a dictionary
dict1 = {1: "one", 2: "two", 3: "three", 4: "four"}
print("Original Dictionary: ", dict1)
# using pop()
valDel = dict1.pop(1)
print("Dictionary after using pop(): ", dict1)
print("The value that was removed is: ", valDel)
# using pop()
valDel = dict1.pop(3)
print("Dictionary after using pop(): ", dict1)
print("The value that was removed is: ", valDel)
# using pop()
valDel = dict1.pop(3, "No Key Found")
print("Dictionary after using pop(): ", dict1)
print("The value that was removed is: ", valDel)
# using pop()
# if default value not given, error will be raised
print("Error raised: ")
valDel = dict1.pop(3)

Method 4: Remove multiple keys from a dictionary using the pop() method

We can delete multiple key-value pairs from the dictionary using the pop() method in a for loop. First, we declare an array of keys that need to be removed from the dictionary, then use a loop to iterate, and lastly remove them from the dictionary using the pop() method one by one.

# declare a dictionary
dict1 = {1: "one", 2: "two", 3: "three", 4: "four"}
removeKeys = [2,3]
for key in removeKeys:
  dict1.pop(key)
print(dict1)

Method 5: Delete all key-value pairs from a dictionary using the del keyword

We can delete all the key-value pairs from a dictionary using the del keyword as demonstrated in the code below:

# declare a dictionary
dict1 = {1: "one", 2: "two", 3: "three", 4: "four"}
print("Original Dictionary: ", dict1)
del dict1
try:
    print(test_dict)
except:
    print('All elements are deleted!')

Quiz!

1

Which statement is correct for removing all the key-value pairs using the del keyword?

A)

delete dict_name

B)

del dict_name[key]

C)

del dict_name

D)

del dict_name.delete()

Question 1 of 30 attempted

In conclusion, knowing how to delete key-value pairs is an essential skill for managing data structures. Effective use of keywords/methods like del, pop() and popitem() will help in data manipulation in our projects.

Frequently asked questions

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How do we remove the last key-value pair from a dictionary in Python?

We can remove the last key-value pair from a dictionary using the in-built function popitem().

How do we remove elements from a set in Python?

We can remove elements from a set using the Python remove() method.

colors = {"yellow", "green", "red"}
colors.remove("green")
print(colors)

What happens if we try to remove a key that does not exist in the dictionary?

If we try to remove a key that does not exist, a KeyError exception is raised.

How do we sort a dictionary by value in Python?

We can sort a dictionary by value in Python using the sorted() method:

dict1 = {1: "one", 2: "two", 3: "three", 4: "four"}

lst = dict1.values()

#Sorted by value
print("Sorted by value: ", sorted(lst))

How do we check if a dictionary is empty in Python?

We can check if a dictionary is empty using a simple if not statement or the len() function.

if not newDict:
    print("Dictionary is empty")
//or
if len(newDict) == 0:
    print("Dictionary is empty")

What is a Python hash table?

A Python hash table contains key-value pairs, but the key is created using a hashing function. As a result, a data element’s search and insertion functions become considerably faster, since the key values themselves become the index of the array that holds the data.

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