python

fn = lambda x: x**3
fn(2)
8

(lambda x: x**3)(2)
8

(lambda x: [x * _ for _ in range(10)])(3)
[0, 3, 6, 9, 12, 15, 18, 21, 24, 27]

def (): 
    ........
    ........

## First Declare a function 
def ():
    .......
    .......


fn_name.__name__
'fn_name'

## Document a function with three single quotes
def check():
    '''This function is documented'''
    return


>>> check.__doc__
'This function is documented'

>>> def multiply(a, b=0): ## b is 0 by default
...     return a * b
...
>>> multiply(1, 3) ## 3 * 1
3
>>> multiply(5) ## 5 * 0
0
>>> multiply(5, b=3) ## 5 * 3
15

def count(start, step):
    while True:
        yield start
        start += step

>>> counter = count(10, 5)
>>> next(counter)
(15)

>>> next(counter) ## Increments by 5 from the previous result
(20)

>>> next(counter)
(25)

>>> next(counter), next(counter), next(counter)
(30, 35, 40)

>>> from functools import wraps

>>> def decorator_func(func):
...     @wraps(func)
...     def wrapper(*args, **kwargs):
...         print("Before calling {}.".format(func.__name__))
...         ret = func(*args, **kwargs)
...         print("After calling {}.".format(func.__name__))
...         return ret
...     return wrapper
...
>>> @decorator_func
... def check():
...     print("Inside check function.")
...
>>> check()
Before calling check.
Inside check function.
After calling check.