# functions.py
'''
A few basic examples regarding functions.
'''

#
# User defined functions.
#

def my_fun(a, b):
    '''
    Does something.
    Always add some documentation.
    '''
    a += 1
    if a > 3:
        return a + b
    else:
        return a, b
    print('after return')

myFun(4, 5)
myFun?
myFun??
x = 4
y = 5
print(my_fun(x, y))
print(x)

# The scope of the variables is the function itself.

# Functions can make use of global variables.
x = 3
def my_fun(a, b):
    '''
    Does something.
    Always add some documentation.
    '''
    a += 1
    return a + b + x
print(my_fun(4, 5))


# Return more than one value.
def my_fun(a, b):
    '''
    Does something.
    Always add some documentation.
    '''
    return a**2, abs(b)
x, y = my_fun(2, -3)

# my_fun returns a tuple. Its elements can be accessed like list elements.
x = my_fun(2, -3)[0]
y = my_fun(2, -3)[1]


#
# Recursion.
#
def factorial(n):
    '''
    Computes the factorial.
    '''

    if (type(n) != int) or (n < 0):
        print("error: input value invalid")
        return (-1)

    if (n == 0):
        return 1
    else:
        return n*factorial(n-1)


#
# Argument values, keywords.
#
def my_fun(a, b, x=4, y=7):
    '''
    A function with default arguments.
    '''

    return (a + b)*x + y

my_fun(2, 3)
my_fun(2, 3, 1)
my_fun(2, 3, x=1)
my_fun(2, 3, y=1, x=1)