02-03: Input and Output

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input() Function

input() is used to take input from the user through the keyboard.

• It pauses the program and waits for user input
• Whatever the user types is returned as a string (str)
• Optional message (prompt) can be shown to guide the user

✅ Syntax

input("message to user")

✅ Example

name = input("Enter your name: ")
print("Hello", name)

👉 Sample run:

Enter your name: Imran
Hello Imran

💡 Explanation - The program displays → Enter your name: - The user types → Imran - name stores "Imran" (string) - print() displays the result

⚠️ Important Note

age = input("Enter age: ")

• Even if the user enters 25, Python stores it as: "25" # string, not integer

📌 Taking Multiple Inputs

🔹 Simple Way

a = int(input("Enter first number: "))
b = int(input("Enter second number: "))

print("Sum =", a + b)

👉 Sample run:

Enter first number: 10
Enter second number: 20
Sum = 30

🔹 Multiple Inputs in One Line

a, b = map(int, input("Enter two numbers: ").split())

print("Sum =", a + b)

👉 Sample run:

Enter two numbers: 10 20
Sum = 30

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Type Conversion (Casting)

🔹 Why Type Conversion is Needed?

Since input() returns a string, mathematical operations will fail without conversion.

❌ Example (Error)

num = input("Enter a number: ")
print(num + 5)

👉 Error because: - "num" is string - 5 is integer

TypeError: can only concatenate str (not "int") to str

✅ Correct Approach

num = int(input("Enter a number: "))
print(num + 5)

👉 Sample run:

Enter a number: 10
15

🔹 Common Conversion Functions

Function	Description	Example
int()	Converts to integer	int("10") → 10
float()	Converts to decimal	float("3.5") → 3.5
str()	Converts to string	str(100) → "100"

🔹 Float Example

price = float(input("Enter price: "))
print(price * 2)

👉 Sample run:

Enter price: 49.5
99.0

🔹 String Conversion Example

num = 50
text = str(num)
print("Value is " + text)

👉 Output:

Value is 50

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print() Function

print() is used to display output on the screen

• It can print text, numbers, variables, and expressions
• It automatically converts values to string when displaying

✅ Basic Usage

print("Hello World")
print(10)
print("Age:", 25)

👉 Output:

Hello World
10
Age: 25

🔹 Printing Multiple Values

name = "Imran"
age = 25

print("Name:", name, "Age:", age)

👉 Output:

Name: Imran Age: 25

⚙️ Important Parameters of print()

🔹 1. sep (Separator)

Defines how multiple values are separated

print("A", "B", "C", sep="-")

👉 Output:

A-B-C

🔹 2. end (Ending Character)

Controls what is printed at the end

print("Hello", end=" ")
print("World")

👉 Output:

Hello World

🔹 Default Behavior

print("Hello")
print("World")

👉 Output:

Hello
World

👉 Because default end = "\n" (new line)

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📌 Output Formatting

Formatting helps display output in a clear and readable way

🔹 Method 1: Using Comma ,

name = "Imran"
age = 25

print("Name:", name, "Age:", age)

👉 Output:

Name: Imran Age: 25

👉 Simple and beginner-friendly

🔹 Method 2: Using + (Concatenation)

name = "Imran"
print("Hello " + name)

👉 Output:

Hello Imran

⚠️ Only works with strings

print("Age: " + str(25))   # must convert number to string

👉 Output:

Age: 25

🔹 Method 3: format() Method

name = "Imran"
age = 25

print("My name is {} and I am {} years old".format(name, age))

👉 Output:

My name is Imran and I am 25 years old

🔹 Method 4: f-Strings (Best ⭐)

Introduced in Python 3.6

name = "Imran"
age = 25

print(f"My name is {name} and I am {age} years old")

👉 Output:

My name is Imran and I am 25 years old

f-strings are powerful, because: - Clean and readable - Can include variables + expressions

a = 10
b = 5

print(f"Sum = {a + b}")

👉 Output:

Sum = 15

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Formatting Numbers using f-Strings

🔹 Basic Syntax

f"{value:format_specifier}"

🔹 1.1 Decimal Precision

Example:

pi = 3.1415926535

print(f"{pi:.2f}")

👉 Output:

3.14

💡 Explanation

.2f → 2 decimal places

f → float

Examples

num = 5

print(f"{num:.2f}")

👉 Output:

5.00

🔹 1.2 Width & Alignment

num = 25

print('*****')
print(f"{num:5}")

👉 Output:

*****
   25

Alignment Types

print('*****')
print(f"{25:<5}")  # Left
print(f"{25:>5}")  # Right
print(f"{25:^5}")  # Center
print('*****')

👉 Output:

*****
25   
   25
 25  
*****

🔹 1.3 Zero Padding

num = 7

print(f"{num:05}")

👉 Output:

00007

🔹 1.4 Comma Separator

num = 1000000

print(f"{num:,}")

👉 Output:

1,000,000

🔹 1.5 Percentage Formatting

value = 0.85

print(f"{value:.2%}")

👉 Output:

85.00%

🔹 1.6 Scientific Notation

num = 123456

print(f"{num:.2e}")

👉 Output:

1.23e+05

🔹 1.7 Combining Everything

num = 12345.6789

print(f"{num:,.2f}")

👉 Output:

12,345.68

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Combined Example (Real Use)

name = input("Enter your name: ")
age = int(input("Enter your age: "))
height = float(input("Enter your height: "))

print(f"\n--- User Information ---")
print(f"Name   : {name}")
print(f"Age    : {age}")
print(f"Height : {height:.2f}")
print(f"In 5 years, age will be {age + 5}")

👉 Sample run:

Enter your name: Imran
Enter your age: 25
Enter your height: 5.9

--- User Information ---
Name   : Imran
Age    : 25
Height : 5.90
In 5 years, age will be 30

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Quick Summary

• input() → takes input (always string)
• print() → displays output
• sep → controls separator
• end → controls line ending
• int(), float(), str() → type conversion
• f-strings → best for formatting

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Practice Problems

# Problem 1
name = input("Enter name: ")
print(f"Welcome {name}")

# Problem 2
num = int(input("Enter a number: "))
print(f"Square = {num * num}")

# Problem 3
a, b = map(int, input("Enter two numbers: ").split())
print(f"Sum = {a + b}, Difference = {a - b}")

👉 Sample run:

Enter name: Imran
Welcome Imran
Enter a number: 6
Square = 36
Enter two numbers: 10 4
Sum = 14, Difference = 6

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Exercises: 02-03: Exercises — Input and Output

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⬅️ Previous: 02-02: Variables and Data Types ➡️ Next: 02-04: Operators