This session is all about functions → creating them, passing arguments, scope, and the functional-programming tools (lambda, map, filter, reduce).

Creating a function (with docstring)

A function is a reusable block of code. The triple-quoted text right under the def line is a docstring → a short description of what the function does.

def is_even(num):
    """
    This function returns if a given number is odd or even
    input - any valid integer
    output - odd/even
    created on - 16th Nov 2022
    """
    if type(num) == int:
        if num % 2 == 0:
            return 'even'
        else:
            return 'odd'
    else:
        return 'pagal hai kya?'

Calling it in a loop:

for i in range(1,11):
    x = is_even(i)
    print(x)
# odd
# even
# odd
# even
# ... (keeps alternating up to 10)

Docstrings

Every function's docstring is stored in __doc__. Even built-in types have one:

print(type.__doc__)
# type(object_or_name, bases, dict)
# type(object) -> the object's type
# type(name, bases, dict) -> a new type

(The -> here is part of Python's own docstring text, not a connector.)

Two points of view

There are two sides to a function: the creator and the user. The creator thinks about edge cases (like someone passing a string instead of a number), the user just calls it and gets a result.

is_even('hello')   # 'pagal hai kya?'   (the else branch handles non-integers)

Parameters vs Arguments

• A parameter is the name in the function definition (like num above).
• An argument is the actual value you pass in when calling (like 'hello' or 4).

Types of Arguments

Three kinds: default, positional, and keyword.

def power(a=1, b=1):   # a and b have DEFAULT values
    return a**b

power()          # 1     (uses the defaults, 1**1)
power(2,3)       # 8     (positional: a=2, b=3)
power(b=3, a=2)  # 8     (keyword: name them directly, order does not matter)

args and *kwargs