ReactCHALLENGES

13. Lambda

A lambda is a small anonymous function written in a single expression:

  • parameters — zero or more parameters, separated by commas, like in def.
  • expression — a single expression; its value is returned automatically. There is no return and no block of statements.

Lambdas are often passed directly to functions that expect a function, such as sorted(key=...) or map():

  • sorted(iterable, key=...) orders the elements by the value returned by key.
  • map(function, iterable) applies the function to each element. Wrap it in list() to see the results.

Coming from JavaScript? A lambda is an arrow function with an expression body: lambda n: n * 2 is (n) => n * 2. The body must be one expression (no block, no return, no if statement), and a lambda captures the variable, not its value:

#01

Store a lambda in a variable

Assign a lambda to the variable double. It takes one parameter n and returns n * 2. Print double(5).

Print exactly:

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#02

A lambda with two parameters

Assign a lambda to the variable add. It takes two parameters a and b and returns their sum. Print add(2, 3).

Print exactly:

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#03

Use a lambda as a sort key

Use words = ["bbb", "a", "cc"]. Sort the list with sorted() and pass a lambda as the key argument. The lambda returns the length of a word, so the list is ordered from the shortest word to the longest. Print the sorted list.

Print exactly:

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#04

Use a lambda with map

Use numbers = [1, 2, 3]. Use map() with a lambda that squares its argument, wrap the result in list() and print it.

Print exactly:

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