Remove Unwanted Keys Associations - Python

We are given a dictionary we need to remove the unwanted keys from the dictionary. For example, a = {'a': 1, 'b': 2, 'c': 3, 'd': 4} is a dictionary we need to remove the unwanted keys from the dictionary so that the output becomes {'a':1, 'c':3} .

Using del Statement

del statement is used to remove specific key-value pairs from a dictionary by specifying the key to delete. It modifies the dictionary in place and raises a KeyError if the key does not exist.

a = {'a': 1, 'b': 2, 'c': 3, 'd': 4}
del a['b']  # Remove key 'b'
del data['d']  # Remove key 'd'
print(a)

{'a': 1, 'c': 3}

Explanation:

• del statement removes the specified keys 'b' and 'd' from the dictionary data, eliminating their associated values.
• After the deletions, the dictionary is updated to only include the remaining key-value pairs, resulting in {'a': 1, 'c': 3}

Using Dictionary Comprehension

Dictionary comprehension allows filtering a dictionary by creating a new one with only the desired keys and values. This is done by iterating over the dictionary and including key-value pairs that meet the specified condition

a = {'a': 1, 'b': 2, 'c': 3, 'd': 4}

# Set of keys to keep
b = {'a', 'c'}

# Dictionary comprehension to filter and retain only the keys present in 'b'
res = {key: a[key] for key in b}

print(res)

{'c': 3, 'a': 1}

Explanation:

• Set b specifies the keys to keep, and the dictionary comprehension {key: a[key] for key in b} iterates through these keys extracting their corresponding values from the dictionary a.
• Resulting dictionary, res, includes only the key-value pairs for the keys 'a' and 'c', producing {'a': 1, 'c': 3}

Using pop()

pop() method removes a specific key from the dictionary and returns its value, modifying the dictionary in place. If the key doesn't exist a default value (like None) can be provided to avoid a KeyError.

a = {'a': 1, 'b': 2, 'c': 3, 'd': 4}
a.pop('b', None)  # Remove 'b', ignore if not present
a.pop('d', None)  # Remove 'd', ignore if not present
print(a)

{'a': 1, 'c': 3}

Explanation:

• pop('b', None) and pop('d', None) statements remove the keys 'b' and 'd' from the dictionary a, along with their associated values, without raising an error if the keys are missing.
• After these operations, the updated dictionary contains only remaining key-value pairs, resulting in {'a': 1, 'c': 3}