Functions

The basics about functions

Defining and calling a function

Example

#!/usr/bin/env python3

def my_function():
    print("Hello from a function")


def main():
    my_function()


if __name__ == "__main__":
    main()

Calling a function multiple time and scope of the variables

Example

#!/usr/bin/env python3

def my_function(fname):
    print(fname + " Refsnes")


def main():
    my_function("Emil")
    my_function("Tobias")
    my_function("Linus")


if __name__ == "__main__":
    main()

Using return

Example

#!/usr/bin/env python3

def my_function(x):
    return 5 * x


def main():
    print(my_function(3))
    print(my_function(5))
    print(my_function(9))


if __name__ == "__main__":
    main()

Default values

Example

#!/usr/bin/env python3

def my_function(country = "Norway"):
    print("I am from " + country)


def main():
    my_function("Sweden")
    my_function("India")
    my_function()
    my_function("Brazil")


if __name__ == "__main__":
    main()

Passing multiple arguments

Index based with *args

Example

#!/usr/bin/env python3

def my_function(*kids):
    print("The youngest child is " + kids[2])


def main():
    my_function("Emil", "Tobias", "Linus")


if __name__ == "__main__":
    main()

Keyword based with **kwargs

Example

#!/usr/bin/env python3

def my_function(**kid):
    print("His last name is " + kid["lname"])


def main():
    my_function(fname = "Tobias", lname = "Refsnes")


if __name__ == "__main__":
    main()

Using yield instead of return

Example

#!/usr/bin/env python3

def multi_yield():
    yield_str = "This will print the first string"
    yield yield_str
    yield_str = "This will print the second string"
    yield yield_str


def main():
    multi_obj = multi_yield()
    print(next(multi_obj))
    print(next(multi_obj))
    print(next(multi_obj))


if __name__ == "__main__":
    main()

Map, Filter and Reduce

The map() function executes a specified function for each item in an iterable. The item is sent to the function as a parameter.

Example

#!/usr/bin/env python3

def my_function(n):
    return len(n)


def main():
    x = map(my_function, ('apple', 'banana', 'cherry'))
    prin(x)
    print(list(x))


if __name__ == "__main__":
    main()

The filter() function returns an iterator were the items are filtered through a function to test if the item is accepted or not.

Example

#!/usr/bin/env python3

def my_function(x):
    if x < 18:
        return False
    else:
        return True


def main():
    ages = [5, 12, 17, 18, 24, 32]
    adults = filter(my_function, ages)
    print(list(adults))


if __name__ == "__main__":
    main()

The functools.reduce()

Example

#!/usr/bin/env python3

from functools import reduce

def my_function(a, b):
    result = a + b
    print(f"{a} + {b} = {result}")
    return result


def main():
    numbers = [0, 1, 2, 3, 4]
    reduce(my_function, numbers)


if __name__ == "__main__":
    main()

Introduction to Lambda

A lambda function is an anonymous function

Syntax

lambda arguments : expression

Example

#!/usr/bin/env python3

def main():
    x = lambda a : a + 2
    print(x(2))


if __name__ == "__main__":
    main()

Output

4

Example

#!/usr/bin/env python3

def main():
    x = lambda a, b : a + b
    print(x(2, 3))


if __name__ == "__main__":
    main()

Output

5

Using Lambda functions

Example

#!/usr/bin/env python3

def myDouble(x):
    return lambda a : a * x


def main():
    double = myDouble(2)
    print(double(3))
    print(double(4))


if __name__ == "__main__":
    main()

Output

6
8