Python Functions Tutorial¶

1. Function Definition, Parameters, and Return Statements¶

• Functions are defined using the def keyword.
• Parameters are inputs to functions.
• return sends back a result from the function.

In [ ]:

def greet(name):
    greeting_sentence = f"Hello, {name}!" 
    return greeting_sentence

greeting_sentence = greet("Alice")
print(greeting_sentence)

def greet(name): greeting_sentence = f"Hello, {name}!" return greeting_sentence greeting_sentence = greet("Alice") print(greeting_sentence)

Hello, Alice!

In [4]:

def is_even(n):
    if n % 2 == 0:
        return True
    else:
        return False 

number = 5
is_even(number)

def is_even(n): if n % 2 == 0: return True else: return False number = 5 is_even(number)

Out[4]:

False

In [5]:

def sqaure_cube(number_list):
    print(number_list)

num_list = [1, 2, 6, 5, 8, 2]
sqaure_cube(num_list)

def sqaure_cube(number_list): print(number_list) num_list = [1, 2, 6, 5, 8, 2] sqaure_cube(num_list)

[1, 2, 6, 5, 8, 2]

Exercise 1¶

Q1 : Write a function area_of_rectangle(length, width) that returns the area of a rectangle.¶

Q2 : Create a function is_even(number) that returns True if the number is even, otherwise False.¶

Q3 : Create a function that takes a list of number as parameter, and return the list with sqaure of even numbers and cube of odd numbers. The order of number should be preserved.¶

Input : [5, 3, 6, 7, 1, 2]

Output : [125, 27, 36, 343, 1, 4]

Q4 : Write a Python function that takes a list of words as input and returns a dictionary showing how many times each word appears in the list.¶

Input : 

words = ['apple', 'banana', 'apple', 'orange', 'banana', 'apple']

Output : 

{'apple': 3, 'banana': 2, 'orange': 1}

Q5 : Write a Python function that calculates the average grade for each student given a dictionary of their scores.¶

Hint : sum([1, 2, 3]) provides sum of a list

input : 

grades = {
    'Alice': [85, 90, 78],
    'Bob': [70, 80, 65],
    'Charlie': [100, 95, 90]
}


output : 

{
    'Alice': 84.33,
    'Bob': 71.67,
    'Charlie': 95.0
}

In [ ]:

grades_dictionary = {
    'Alice': [85, 90, 78],
    'Bob': [70, 80, 65],
    'Charlie': [100, 95, 90]
}

output_dictionary = {}

for grade in grades_dictionary.items():
    student_name, students_grades = grade 
    student_average_grade = sum(students_grades) / len(students_grades)

    output_dictionary[student_name] = student_average_grade

print(output_dictionary)

grades_dictionary = { 'Alice': [85, 90, 78], 'Bob': [70, 80, 65], 'Charlie': [100, 95, 90] } output_dictionary = {} for grade in grades_dictionary.items(): student_name, students_grades = grade student_average_grade = sum(students_grades) / len(students_grades) output_dictionary[student_name] = student_average_grade print(output_dictionary)

{'Alice': 84.33333333333333, 'Bob': 71.66666666666667, 'Charlie': 95.0}

In [11]:

def averageGrades(grades_dictionary):
    output_dictionary = {}

    for grade in grades_dictionary.items():
        student_name, students_grades = grade 
        student_average_grade = sum(students_grades) / len(students_grades)

        output_dictionary[student_name] = student_average_grade

    return output_dictionary

def averageGrades(grades_dictionary): output_dictionary = {} for grade in grades_dictionary.items(): student_name, students_grades = grade student_average_grade = sum(students_grades) / len(students_grades) output_dictionary[student_name] = student_average_grade return output_dictionary

In [13]:

grades_dictionary = {
    'Alice': [85, 90, 78],
    'Bob': [70, 80, 65],
    'Charlie': [100, 95, 90]
}

average_grades_dictionary = averageGrades(grades_dictionary)
print(average_grades_dictionary)

grades_dictionary = { 'Alice': [85, 90, 78], 'Bob': [70, 80, 65], 'Charlie': [100, 95, 90] } average_grades_dictionary = averageGrades(grades_dictionary) print(average_grades_dictionary)

{'Alice': 84.33333333333333, 'Bob': 71.66666666666667, 'Charlie': 95.0}

In [ ]:

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In [5]:

def wordCounter(words):
    output_dictionary = {}

    for w in words:
        if w not in output_dictionary.keys():
            output_dictionary[w] = 1
        else:
            output_dictionary[w] = output_dictionary[w] + 1
    
    return output_dictionary

def wordCounter(words): output_dictionary = {} for w in words: if w not in output_dictionary.keys(): output_dictionary[w] = 1 else: output_dictionary[w] = output_dictionary[w] + 1 return output_dictionary

In [6]:

words = ['apple', 'banana', 'apple', 'orange', 'banana', 'apple']

counter_dictionary = wordCounter(words)
print(counter_dictionary)

words = ['apple', 'banana', 'apple', 'orange', 'banana', 'apple'] counter_dictionary = wordCounter(words) print(counter_dictionary)

{'apple': 3, 'banana': 2, 'orange': 1}

2. Default Parameters, Keyword Arguments, and Docstrings¶

• Default parameters are used when an argument is not passed.
• Keyword arguments allow passing parameters by name.
• Docstrings are string literals used to describe functions.

In [ ]:

'''
this is a 
multiline
string
'''

''' this is a multiline string '''

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def power(base, exponent=2):
    ''' 
    base is raised to the power of exponent

    Input: 
        base : 
        exponent:
    
    Output:
        base ** exponent is the output of the function
    '''
    return base ** exponent

print(power(3))
power(2, 3)
outup_number = power(
    base = 10,
    exponent=2
)
print(outup_number)

def power(base, exponent=2): ''' base is raised to the power of exponent Input: base : exponent: Output: base ** exponent is the output of the function ''' return base ** exponent print(power(3)) power(2, 3) outup_number = power( base = 10, exponent=2 ) print(outup_number)

9
100

In [28]:

help(power)

help(power)

Help on function power in module __main__:

power(base, exponent=2)
    base is raised to the power of exponent

    Input:
        base :
        exponent:

    Output:
        base ** exponent is the output of the function

In [ ]:

print(power.__doc__)

print(power.__doc__)

In [3]:

help(power)

help(power)

Help on function power in module __main__:

power(base, exponent=2)
    Returns the base raised to the power of exponent.

Exercise 2¶

Q3 : Write a function greet(name, message="Welcome!") that prints a greeting. Demonstrate it with default and keyword arguments.¶

Output : Welcome! Alice

Q4 : Define a function multiply(a, b=2) with a docstring. Call it using positional and keyword arguments.¶

In [30]:

def greet(name, message = 'Welcome!'):
    greeting_sentence = f'{message} {name}'
    print(greeting_sentence)

greet('Alice')
greet('Charlie', message = 'Thank You!')

def greet(name, message = 'Welcome!'): greeting_sentence = f'{message} {name}' print(greeting_sentence) greet('Alice') greet('Charlie', message = 'Thank You!')

Welcome! Alice
Thank You! Charlie

3. *args and **kwargs¶

• *args allows variable number of positional arguments.
• **kwargs allows variable number of keyword arguments.

In [31]:

def tempFunction1(*args):
    print(args)
    print(type(args))

tempFunction1(1, 2, 4, 5, 'Hello')

def tempFunction1(*args): print(args) print(type(args)) tempFunction1(1, 2, 4, 5, 'Hello')

(1, 2, 4, 5, 'Hello')
<class 'tuple'>

In [8]:

def tempFunction2(**kwargs):
    print(kwargs)
    print(kwargs['name'])

tempFunction2(name = 'nirajan', location = 'bkt')        

def tempFunction2(**kwargs): print(kwargs) print(kwargs['name']) tempFunction2(name = 'nirajan', location = 'bkt')

{'name': 'nirajan', 'location': 'bkt'}
nirajan

In [4]:

def show_args(*args, **kwargs):
    print("Positional arguments:", args)
    print("Keyword arguments:", kwargs)

show_args(1, 2, 3, name="Alice", age=25)

def show_args(*args, **kwargs): print("Positional arguments:", args) print("Keyword arguments:", kwargs) show_args(1, 2, 3, name="Alice", age=25)

Positional arguments: (1, 2, 3)
Keyword arguments: {'name': 'Alice', 'age': 25}

In [20]:

def func3(a, *args, **kwargs):
    print(a)
    print(args)
    print(kwargs)


func3(1, 'apple', 'mango', fruit = 'grapes', city = 'pokhara')

def func3(a, *args, **kwargs): print(a) print(args) print(kwargs) func3(1, 'apple', 'mango', fruit = 'grapes', city = 'pokhara')

1
('apple', 'mango')
{'fruit': 'grapes', 'city': 'pokhara'}

In [32]:

def sum_all(*numbers):
    print(sum(numbers))

sum_all(1, 2, 3, 5, 2, 3)

def sum_all(*numbers): print(sum(numbers)) sum_all(1, 2, 3, 5, 2, 3)

16

Exercise¶

Q5 : Write a function sum_all(*numbers) that returns the sum of all arguments passed to it.¶

Q6 : Create a function print_student_details(**details) that prints each key-value pair passed as keyword arguments.¶

Hint: Use dict.items() function

Function call:

print_student_details(name="Sita", age=20, grade="A", address="Kathmandu")

Output:

name: Sita
age: 20
grade: A
address: Janakpur

4. Scope: Local, Global, and Nonlocal¶

• Local: Defined inside a function.
• Global: Defined at the top level.

In [39]:

x = 10

x = 10

In [41]:

def func2():
    global x
    print(x)

func2()

def func2(): global x print(x) func2()

10

In [38]:

def func1():
    x = 20
    print('inside function : ', x)

func1()
print('outside function : ', x)

def func1(): x = 20 print('inside function : ', x) func1() print('outside function : ', x)

inside function :  20
outside function :  10

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In [4]:

x = 'this is a global variable'

def func1():
    x = 'this is a local variable'
    print(x) ## --> local variable


func1()
print(x) # --> global variable

x = 'this is a global variable' def func1(): x = 'this is a local variable' print(x) ## --> local variable func1() print(x) # --> global variable

this is a local variable
this is a global variable

5. Methods vs. Functions¶

• Functions are defined using def and are independent.
• Methods are functions associated with objects (e.g., strings, lists).

In [ ]:

# Function
def add(a, b):
    return a + b

# Method (associated with string object)
text = "hello"
print(text.upper())

print(add(5, 10))

# Function def add(a, b): return a + b # Method (associated with string object) text = "hello" print(text.upper()) print(add(5, 10))

In [42]:

list1 = [1, 2, 3, 4, 5]
list2 = [4, 5, 6, 7, 8]

intersection_list = []

for number in list1:
    if number in list2:
        intersection_list.append(number)

print(intersection_list)

list1 = [1, 2, 3, 4, 5] list2 = [4, 5, 6, 7, 8] intersection_list = [] for number in list1: if number in list2: intersection_list.append(number) print(intersection_list)

[4, 5]

Problem Solving Exercise¶

Q7: Common Elements Between Two Lists¶

Write a function common_elements(list1, list2) that returns a list of elements common to both lists.

Q8: Second Largest Element¶

Write a function second_largest(lst) that returns the second largest number in a list.

Q9: Rotate List Elements¶

Write a function rotate_list(lst, k) that rotates the list k steps to the right.

Input:

lst = [1, 2, 3, 4, 5, 6, 7]
k = 3

Output:

[5, 6, 7, 1, 2, 3, 4]

In [ ]:

lst = [1, 2, 3, 4, 5, 6, 7]
k = 3

lst = [1, 2, 3, 4, 5, 6, 7] k = 3

Out[ ]:

['mango', 'apple']

In [ ]: