Python - Ways to invert mapping of dictionary

Dictionary is a collection which is unordered, changeable and indexed. In Python, dictionaries are written with curly brackets, and they have keys and values. Inverting a dictionary means swapping keys and values, so the original values become the new keys and vice versa.

Using Dictionary Comprehension

The most Pythonic way to invert a dictionary is using dictionary comprehension ?

# initialising dictionary
ini_dict = {101: "vishesh", 201: "laptop"}

# print initial dictionary
print("initial dictionary:", ini_dict)

# inverse mapping using dict comprehension
inv_dict = {v: k for k, v in ini_dict.items()}

# print final dictionary
print("inverse mapped dictionary:", inv_dict)

initial dictionary: {101: 'vishesh', 201: 'laptop'}
inverse mapped dictionary: {'vishesh': 101, 'laptop': 201}

Using zip() and dict() Functions

The zip() function pairs values with keys, then dict() creates the inverted dictionary ?

# initialising dictionary
ini_dict = {101: "vishesh", 201: "laptop"}

# print initial dictionary
print("initial dictionary:", ini_dict)

# inverse mapping using zip and dict functions
inv_dict = dict(zip(ini_dict.values(), ini_dict.keys()))

# print final dictionary
print("inverse mapped dictionary:", inv_dict)

initial dictionary: {101: 'vishesh', 201: 'laptop'}
inverse mapped dictionary: {'vishesh': 101, 'laptop': 201}

Using map() and reversed()

The map() function applies reversed() to each key-value tuple, swapping their positions ?

# initialising dictionary
ini_dict = {101: "akshat", 201: "ball"}

# print initial dictionary
print("initial dictionary:", ini_dict)

# inverse mapping using map and reversed
inv_dict = dict(map(reversed, ini_dict.items()))

# print final dictionary
print("inverse mapped dictionary:", inv_dict)

initial dictionary: {101: 'akshat', 201: 'ball'}
inverse mapped dictionary: {'akshat': 101, 'ball': 201}

Using Lambda Function

You can create a lambda function that returns an inverted dictionary ?

# initialising dictionary
ini_dict = {101: "akshat", 201: "ball"}

# print initial dictionary
print("initial dictionary:", ini_dict)

# inverse mapping using lambda
invert_dict = lambda d: {v: k for k, v in d.items()}
inv_dict = invert_dict(ini_dict)

# print final dictionary
print("inverse mapped dictionary:", inv_dict)

initial dictionary: {101: 'akshat', 201: 'ball'}
inverse mapped dictionary: {'akshat': 101, 'ball': 201}

Comparison

Conclusion

Dictionary comprehension is the most readable and efficient method for inverting dictionaries. Use zip() with dict() for functional programming style, and lambda functions when you need a reusable inversion function.