How to pass a variable number of arguments to a function?

Practicing Coding Interview Questions in Python

Kirill Smirnov

Data Science Consultant, Altran

Argument types

There are two types of arguments:

 

Argument types

There are two types of arguments:

• positional arguments

 

Argument types

There are two types of arguments:

• positional arguments
• keyword arguments

 

Argument types

There are two types of arguments:

• positional arguments
• keyword arguments

 

Positional arguments

def func_with_pos_args(arg1, arg2):

    pass

def multiply(x, y):
    return x * y

multiply(2, 3)

6

*args

def func_with_var_pos_args(*args):

    pass

func_with_var_pos_args(1, 2, 'hello')

*args

def func_with_var_pos_args(*args):

    print(args)

func_with_var_pos_args(1, 2, 'hello')

(1, 2, 'hello')

*args

def func_with_var_pos_args(*args):
    for arg in args:
        print(arg)

func_with_var_pos_args(1, 2, 'hello')

1
2
'hello'

Redefining multiply()

def multiply(*args):
    result = 1
    for arg in args:
        result = result * arg
    return result

multiply(1, 2, 3):

6

multiply(1, 2, 3, 4)

24

Redefining multiply()

def multiply(*nums):
    result = 1
    for num in nums:
        result = result * num
    return result

multiply(1, 2, 3):

6

multiply(1, 2, 3, 4)

24

Another use of single asterisk *

def multiply(num1, num2, num3):
    return num1 * num2 * num3

multiply(1, 2, 3)

6

Another use of single asterisk *

def multiply(num1, num2, num3):
    return num1 * num2 * num3

nums = (2, 3, 4)

multiply(*nums)

24

nums = [2, 3]
multiply(*nums, 4)

24

Another use of single asterisk *

def multiply(*args):
    result = 1
    for arg in args:
        result = result * arg
    return result

nums = (2, 3, 4, 5)

multiply(*nums)

120

Argument types

There are two types of arguments:

• positional arguments
• keyword arguments

 

Keyword arguments

def func_with_kwargs(arg1=1, arg2=2):

def multiply(x=1, y=2):
    print(str(x) + ' : ' + str(y))

multiply(2, 3)

2 : 3

multiply()

1 : 2

Keyword arguments

def func_with_kwargs(arg1=1, arg2=2):

def multiply(x=1, y=2):
    print(str(x) + " : " + str(y))

multiply(y=5, x=3)

3 : 5

**kwargs

kwargs - keyword arguments

def func_with_var_kwargs(**kwargs):
    print(kwargs)

func_with_var_kwargs(arg1=1, arg2=2, arg3=3)

{arg1: 1, arg2: 2, arg3: 3}

func_with_var_kwargs(1, arg2=2, arg3=3)

TypeError

Redefining multiply()

def multiply_kwargs(**kwargs):
    result = 1
    for (key, value) in kwargs.items():
        print(key + ' = ' + str(value))
        result = result * value
    return result

def multiply(*args):
    result = 1
    for arg in args:
        result = result * arg
    return result

Calling multiply_kwargs()

multiply_kwargs(num1=1, num2=2, num3=3, num4=4)

num1 = 1
num2 = 2
num3 = 3
num4 = 4
24

Another use of double asterisk **

def multiply(num1=1, num2=2, num3=3):
    print('num1 = ' + str(num1))
    print('num2 = ' + str(num2))
    print('num3 = ' + str(num3))
    return num1 * num2 * num3

multiply()

num1 = 1
num2 = 2
num3 = 3
6

Another use of double asterisk **

def multiply(num1=1, num2=2, num3=3):
    print('num1 = ' + str(num1))
    print('num2 = ' + str(num2))
    print('num3 = ' + str(num3))
    return num1 * num2 * num3

nums = {'num1': 10, 'num2': 20, 'num3': 30}

multiply(**nums)

num1 = 10
num2 = 20
num3 = 30
6000

Another use of double asterisk **

def multiply(num1=1, num2=2, num3=3):
    print('num1 = ' + str(num1))
    print('num2 = ' + str(num2))
    print('num3 = ' + str(num3))
    return num1 * num2 * num3

nums = {'num1': 10, 'num3': 30}

multiply(**nums)

num1 = 10
num2 = 2
num3 = 30
600

Another use of double asterisk **

def multiply(num1=1, num2=2, num3=3):
    print('num1 = ' + str(num1))
    print('num2 = ' + str(num2))
    print('num3 = ' + str(num3))
    return num1 * num2 * num3

nums = {'NUM10': 1, 'num2': 2, 'num3': 3}

multiply(**nums)

TypeError

Another use of double asterisk **

def multiply_kwargs(**kwargs):
    result = 1
    for (key, value) in kwargs.items():
        print(key + ' = ' + str(value))
        result = result * value
    return result

nums = {
    'num1': 2, 'num2': 3,
    'num3': 4, 'num4': 5
}

multiply_kwargs(**nums)

num1 = 2
num2 = 3
num3 = 4
num4 = 5
120

Argument order

def func(                                           ):

Argument order

def func(arg1, arg2,                                ):

• arg1, arg2 - positional arguments

Argument order

def func(arg1, arg2, *args,                         ):

• arg1, arg2 - positional arguments
• *args - positional arguments of variable size

Argument order

def func(arg1, arg2, *args, kwarg1, kwarg2,         ):

• arg1, arg2 - positional arguments
• *args - positional arguments of variable size
• kwarg1, kwarg2 - keyword arguments

Argument order

def func(arg1, arg2, *args, kwarg1, kwarg2, **kwargs):

• arg1, arg2 - positional arguments
• *args - positional arguments of variable size
• kwarg1, kwarg2 - keyword arguments
• **kwargs - keyword arguments of variable size

def func(arg1, arg2, *args):

def func(arg1, arg2, **kwargs):

def func(*args, **kwargs):

Let's practice!

Practicing Coding Interview Questions in Python