Lambda functions

These are Anonymous Functions that take multiple inputs and evaluate the output in a single statement. It has the following syntax:

lambda arguments : expression

Syntactic Sugar

A lambda expression creates a function object just like the def statement.

Lundh’s lambda Refactoring Recipe

If you find a piece of code hard to understand because of a lambda, follow this refactoring procedure:

1. Write a comment explaining what that lambda does.
2. Summarise that comment by a single statement.
3. Convert the lambda expression into a def expression with the name you found in (2) and the docstring with the comment you made in (1).
4. Remove the comment and use of the lambda statement with the new function.

Examples

Invert strings

lambda string : string[::-1]

Custom key to sort by

>>> test = [
>>> 	{"name": "julian", "age": 10},
>>> 	{"name": "sandra", "age": 8},
>>> 	{"name": "jemima", "age": 9}
>>> ]
>>> sorted(test, key = lambda entry : entry["age"])
[
	{"name": "sandra", "age": 8},
	{"name": "jemima", "age": 9},
	{"name": "julian", "age": 10}
]