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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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))
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,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.
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)