We can create anonymous functions, known as lambda functions. Lambda functions are different from normal Python functions, they origin from Lambda Calculus. It allows you to write very short functions.

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• Practice Python with interactive exercises
• Practice Python with interactive exercises

Lambda function example This code shows the use of a lambda function:

#!/usr/bin/env python
f = lambda x : 2 * x
print f(3)

A return statements is never used in a lambda function, it always returns something. A lambda functions may contain if statements:

#!/usr/bin/env python
f = lambda x: x > 10
print(f(2))
print(f(12))

map function

The definition of map is map(function,iterable). It applies a function to every item in the iteratable.  We can use map() to on a lambda function with a list:

#!/usr/bin/env python
list = [1,2,3,4,5]
squaredList = map(lambda x: x*x, list)
print(squaredList)

Anywhere you use lambda functions, you could use normal functions instead.  A lambda function is not a statement, it is an expression. Lambda functions do not support a block of statements.

filter function

filter(function,iterable) creates a new list from the elmeents for which the function returns True. Example:

#!/usr/bin/env python
list = [1,2,3,4,5,6,7,8,9,10]
newList = filter(lambda x: x % 2 == 0, list)
print(newList)

The returning list returns contains only the elements for which the lambda expression "lamba x: x % 2 == 0"  is true.

reduce function

The reduce function, reduce(function, iterable) applies two arguments cumulatively to the items of iterable, from left to right. Example:

#!/usr/bin/env python
list = [1,2,3,4,5]
s = reduce(lambda x,y: x+y,  list)
print(s)

In this case the expression is always true, thus it simply sums up the elements of the list. Another example:

#!/usr/bin/env python
list = [10,6,7,5,2,1,8,5]
s = reduce(lambda x,y: x if (x > y) else y, list)
print(s)