1. What is a function?
    • A function is a block of code that performs a specific task.
    • It can take inputs, perform operations, and return outputs.
    • It helps in reusability of code and makes the code modular.
  2. Defining a function:
    • A function is defined using the def keyword followed by the function name and parameters in parentheses.
    • The code block inside the function is indented.
  3. Parameters and arguments:
    • Parameters are the variables defined in the function header.
    • Arguments are the values passed to the function when it is called.
  4. Return statement:
    • The return statement is used to return a value from the function.
    • If the return statement is omitted, the function returns None.
  5. Calling a function:
    • A function is called by using its name followed by parentheses and the arguments.
    • The returned value can be stored in a variable.
  6. Default parameters:
    • Default parameters have a default value, which is used if no argument is provided.
    • They are defined using the equals sign after the parameter name.
  7. Keyword arguments:
    • Keyword arguments are used to pass arguments to a function using the parameter name.
    • They are defined using the parameter name followed by the equals sign and the argument value.
  8. Variable scope:
    • Variables defined inside a function have local scope and are not accessible outside the function.
    • Variables defined outside a function have global scope and are accessible inside the function.
  9. Lambda functions:
    • Lambda functions are anonymous functions that are defined using the lambda keyword.
    • They are useful for creating small, one-line functions.
  10. Recursion:
    • Recursion is a technique where a function calls itself.
    • It can be useful for solving problems that can be broken down into smaller sub-problems.

Examples

Simple function:

Define a function that takes two numbers as arguments and returns their sum. Call the function with different arguments to show how it works.

def add_numbers(a, b):
    return a + b

# Run the function
print(add_numbers(5, 3)) 
print(add_numbers(2, 7))

Default parameters:

Define a function that takes two numbers as arguments and returns their product. Set the default value of the second parameter to 1. Call the function with different arguments to show how it works.

def multiply_numbers(a, b=1):
    return a * b

# Run the function
print(multiply_numbers(5)) 
print(multiply_numbers(2, 7))
Lecture 6 - Functions - March 1, 2023

Lecture 6 - Functions

March 1, 2023

6.1 What is a function

  1. A function is a block of code that performs a specific task.
  2. It can take inputs, perform operations, and return outputs.
  3. It helps in reusability of code and makes the code modular.

6.2 How to define a function

  1. Start a functon with def
  2. Write name of the function
  3. Add parentheses ( )
  4. Write the parameters (variables that the function will recieve)
  5. Add :
  6. Make sure that the code starts as indented block on the next line

Example 1: Add numbers

Create a function for sum of two numbers

In [1]:
def add_numbers(a, b):
    return a+b
In [2]:
# Call this function
add_numbers(123, 345)
Out[2]:
468

Example 2: Average

Create a function that finds average of two numbers

In [3]:
def average(a, b):
    return (a+b)/2
In [4]:
# Call average function
average(345, 633)
Out[4]:
489.0

Example 3: Average of list

Define avg_list that will accept a list and return its average

In [5]:
def avg_list(z) :
    return sum(z) / len(z)
In [7]:
# call avg_list function

# First create a list
marks = [65,67,98,90,45,89,87,99]

# Find average of the marks list
avg_list(marks)

age = [23,17,25,34,65,27]

avg_list(age)
# See we have reused the same function avg_list
Out[7]:
31.833333333333332

6.3 Default values

We can add default values with the symbol =

Example 4: Product

Define a function for product of two numbers The second parameter (variable) should have a default value of 1

In [10]:
def multiply (a, b = 1) :
    return a * b
In [11]:
# Call with two values
multiply(30, 20)
Out[11]:
600
In [12]:
# Since there is a default value for the second parameter
# We can run this function with one parameter
multiply(30)
Out[12]:
30

Example 5: Product of list

Define a function product_list, it should accept list and return the product of its values

In [27]:
def product_list(z):
    product = 1
    
    # loop through each element of the list
    for i in range(0, len(z)) :
        
        product = z[i] * product

    return product
In [28]:
# Call this function
mylist = [10,2,5,3,2]

product_list(mylist)
Out[28]:
600

Example 6: Add value of list

In [29]:
def sum_list(z):
    sum = 0
    for i in range(0, len(z)) :
        sum = sum + z[i]
    return sum
In [30]:
sum(mylist)
Out[30]:
22