python►a-basics

Python-a10-Functional Programming

This article shows the examples of Functional Programming in python

function composition

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# 1
def inner():
    print('this is the inner function')
    
def outer(func):
    func()
    
outer(inner)  # this is the inner function

# 2
def outer():
    def inner():
        print('this is the inner function')
    return inner

outer()() # this is the inner function

# sorted
animals = ["ferret", "vole", "dog", "gecko"]
print(sorted(animals, key=len)) # ['dog', 'vole', 'gecko', 'ferret']

lambda

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# callable Return whether the object is callable
print(callable(lambda s: s[::-1])) # True

# 2
reverse = lambda s: s[::-1]
print(reverse('This is a test')) # tset a si sihT<

# 3
print((lambda s: s[::-1])('This is a test'))  # tset a si sihT

# 4
print((lambda x, y, z: x + y + z / 3)(1, 2, 3)) # 4.0

# 5
def func(x):
    return x, x ** 2, x ** 3

print(func(3)) #(3, 9, 27)

# 6
print((lambda x: (x, x ** 2, x ** 3))(3)) #(3, 9, 27)

map

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# map returns an iterator
def reverse(s):
    return s[::-1]

animals = ["cat", "dog", "hedgehog", "gecko"]
iterator = map(reverse, animals)
print(iterator)         # <map object at 0x000001ADCF5CFCD0>
print(list(iterator)    # ['tac', 'god', 'gohegdeh', 'okceg']

# 2
print(list(map(lambda s: s[::-1], animals)))    # ['tac', 'god', 'gohegdeh', 'okceg']

# map with multiple iterables
def func(a, b, c):
    return a + b + c

print(list(map(func, [1, 2, 3], [10, 20, 30], [100, 200, 300])))    # [111, 222, 333]

filter

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# 1
def greater_than_100(x):
    return x > 100

print(list(filter(greater_than_100, [1, 3, 5, 100, 200, 300])))     # [200, 300]

reduce

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# 1
from functools import reduce

def add(x, y):
    return x + y

print(reduce(add, [1, 3, 5]))   # 9

# complex
def custom_map(function, iterable):
    from functools import reduce

    return reduce(
        lambda items, value: items + [function(value)],
        iterable,
        []
    )

print(list(custom_map(str, [2, 3, 3, 4, 5]))) # ['2', '3', '3', '4', '5']