# Functional Programming in Python

Contents

Functional programming can also be interesting in **Python**. Here are some useful snippets.

## Lambda

A lambda expression is an **anonymous function**.

```
# Simple power function
f = lambda x: x*x
[f(x) for x in range(10)]
# [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
```

## Map

`map`

is a **higher-order function** that allows to apply a function to every element in an `iterable`

object and it returns itself an `iterable`

.

```
m = map(f, range(10))
list(m)
# [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
```

## Filter

The filter function **tests** each element in an `iterable`

object with a function that returns either `True`

or `False`

.

```
# In this case it's an even filter
even = filter(lambda x: x % 2 == 0, range(10))
list(even)
# [0, 2, 4, 6, 8]
# Combine map and filter
even = map(f, filter(lambda x: x % 2 == 0, range(10)))
list(even)
# [0, 4, 16, 36, 64]
```

## Reduce

Apply function of two arguments cumulatively to the items of sequence, from left to right, so as to **reduce** the sequence to a **single value**.

```
from functools import reduce
reduce(lambda x,y: x+y, range(10))
# 45
```

## Head & Tail

`head`

and `tail`

are idiomatic of functional programming languages.

```
head, *tail = range(10)
head
# 0
tail
# [1, 2, 3, 4, 5, 6, 7, 8, 9]
```

## List Comprehension

```
[n for n in range(10) if n % 2 == 0]
# [0, 2, 4, 6, 8]
```

## Any and All

Check if `any`

or `all`

conditions are met.
They can also be seen as series of logical `or`

and `and`

operators, respectively.

```
any(x > 10 for x in range(10))
# False
all(x >= 0 for x in range(10))
# True
```