Lambda with map() in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a lambda function in Python?

A lambda function is a small anonymous function defined with the lambda keyword. It can take any number of arguments but has only one expression, which is returned.

beginner

What does the map() function do in Python?

map() applies a given function to each item of an iterable (like a list) and returns a map object with the results.

beginner

How do you combine lambda and map() to square each number in a list?

You can write:
list(map(lambda x: x**2, [1, 2, 3])) which returns [1, 4, 9].

intermediate

Why use lambda with map() instead of a regular function?

Using lambda with map() lets you write quick, simple functions inline without defining a separate function with def.

beginner

What type of object does map() return and how do you get a list from it?

map() returns a map object, which is an iterator. To get a list, wrap it with list(), like list(map(...)).

What does this code return?
list(map(lambda x: x + 1, [1, 2, 3]))

A [1, 3, 5]

B [1, 2, 3]

C [0, 1, 2]

D [2, 3, 4]

The lambda adds 1 to each element, so 1+1=2, 2+1=3, 3+1=4.

Which of these is a correct way to use map() with a lambda to double numbers?

A map(x => x * 2, [1, 2, 3])

B map(lambda x: x * 2, [1, 2, 3])

C map(lambda x: x + 2, [1, 2, 3])

D map(double, [1, 2, 3])

Option B uses Python lambda syntax correctly to double each number.

What is the output type of map() before converting it?

A list

B dictionary

C map object (iterator)

D string

map() returns a map object, which is an iterator.

Why might you prefer lambda with map() over a for-loop?

A It allows concise, readable code for simple operations

B It uses less memory

C It is always faster

D It can only be used with lists

Using lambda with map() makes code shorter and clearer for simple tasks.

What will this code output?
list(map(lambda x: x % 2 == 0, [1, 2, 3, 4]))

A [False, True, False, True]

B [1, 2, 3, 4]

C [True, False, True, False]

D [0, 1, 0, 1]

The lambda checks if each number is even, returning True or False accordingly.

Explain how lambda functions work with map() in Python.

Think about how you can quickly change each item in a list without writing a full function.

Describe a real-life example where using lambda with map() would be helpful.

Imagine you want to quickly add tax to a list of prices.