🌱 Phase 1 · Foundations 🟢 Beginner MODULE 05

Input & Output

⏱️ 30 min read

📖 Theory + Code

🧩 5 Quiz Questions

🏗️ 1 Challenge

Your progress in Phase 183%

🎯 What you'll learn: The full power of print() — its sep, end, and formatting parameters. How input() works and why its result is always a string. How to cast user input to numbers, collect multiple inputs in one line, validate input, and build complete interactive console programs.

Section 1

`print()` — In Depth

You've used print() since Lesson 1, but it has several powerful parameters that most beginners never discover. Understanding them makes your output cleaner and more professional.

Parameter	Default	Purpose
*objects	—	One or more values to print, separated by commas
sep	`" "` (space)	String placed between multiple values
end	`"\n"` (newline)	String printed after the last value
file	`sys.stdout`	Where to write output (advanced — file objects)
flush	`False`	Force immediate output (advanced — buffering)

print_params.py

PYTHON

# Default print — sep=" ", end="\n"
print("Python", "is", "great")        # Python is great

# Custom sep — change the separator
print("Python", "is", "great", sep="-")  # Python-is-great
print("2025", "01", "15", sep="/")       # 2025/01/15
print(1, 2, 3, 4, 5, sep=", ")          # 1, 2, 3, 4, 5
print("a", "b", "c", sep="")             # abc (no separator)

# Custom end — don't move to next line
print("Loading", end="...")
print("Done!")                            # Loading...Done!

# Build a line without loops
for i in range(5):
    print(i, end=" ")                      # 0 1 2 3 4
print()  # blank print() to move to next line

# Print nothing — just a blank line
print()
print("After the gap")

Number Formatting in print()

number_formatting.py

PYTHON

pi       = 3.14159265
price    = 1999999.5
percent  = 0.875

# Decimal places with f-strings
print(f"Pi (2dp): {pi:.2f}")            # Pi (2dp): 3.14
print(f"Pi (5dp): {pi:.5f}")            # Pi (5dp): 3.14159

# Thousands separator
print(f"Price: {price:,.2f}")            # Price: 1,999,999.50

# Percentage
print(f"Score: {percent:.1%}")           # Score: 87.5%

# Width padding (right-align numbers in columns)
print(f"{'Name':10} {'Score':>6}")
print(f"{'Ali':10} {95:>6}")
print(f"{'Muhammad':10} {88:>6}")
# Name        Score
# Ali            95
# Muhammad       88

Section 2

`input()` — Getting User Data

The input() function pauses your program, displays a prompt, and waits for the user to type something and press Enter. It always returns a string — no matter what the user typed.

Program reaches input()

Python displays the prompt text you provide and pauses execution — the program freezes, waiting.

User types and presses Enter

Everything the user typed (before Enter) is captured as a single string. The Enter key itself is NOT included.

input() returns the string

The return value is assigned to your variable. Program continues. Always a str — even if the user typed 42.

Terminal — input() in action

$ python3 greet.py

Enter your name: Sara ← user types this

Enter your age: 21 ← user types this

Hello Sara! You were born in 2004.

input_basics.py

PYTHON

# Basic input
name = input("Enter your name: ")
print(f"Hello, {name}!")

# CRITICAL: input() ALWAYS returns a string!
raw_age = input("Enter your age: ")
print(type(raw_age))         # <class 'str'> — even if user typed 21

# Convert to int to do arithmetic
age = int(raw_age)
birth_year = 2025 - age
print(f"You were born in {birth_year}.")

# One-liner: convert immediately on input
age = int(input("Enter your age: "))      # concise
price = float(input("Enter price (PKR): ")) # for decimals

⚠️

The #1 beginner mistake with input()

Forgetting that input() returns a string. If a user types 5 and you try to add 3 without converting, Python gives: TypeError: can only concatenate str (not "int") to str. Always convert with int() or float() before doing maths.

Section 3

Multiple Inputs & split()

Sometimes you want the user to enter several values at once, separated by spaces or commas. Python's .split() combined with input() makes this clean and efficient.

multiple_inputs.py

PYTHON

# Method 1: separate input() calls (simple)
first_name = input("First name: ")
last_name  = input("Last name: ")
print(f"Full name: {first_name} {last_name}")

# Method 2: split() — user types "Ali Khan" in one input
first, last = input("Enter full name: ").split()
print(f"Hi {first}, surname is {last}")

# Method 3: map() — convert multiple values at once
# User types "10 20 30" → three integers
a, b, c = map(int, input("Enter 3 numbers: ").split())
print(f"Sum: {a + b + c}")  # Sum: 60

# User types "5 7" — two floats
x, y = map(float, input("Enter x y: ").split())
print(f"x² + y² = {x**2 + y**2:.2f}")

# Variable number of inputs → list
marks = list(map(int, input("Enter marks separated by spaces: ").split()))
print(f"Total: {sum(marks)}, Average: {sum(marks)/len(marks):.1f}")

💡

How map(int, iterable) works

map(func, iterable) applies func to every item in the iterable and returns a map object. map(int, ["10", "20", "30"]) is equivalent to calling int() on each element. Combined with .split() and tuple unpacking, it's the standard pattern for reading multiple numbers from one line.

Section 4

Input Validation

Real programs can't trust users to type the right thing. Input validation means checking that the user's input is safe before you use it. Even a simple check with .isdigit() or a try/except block can prevent crashes.

input_validation.py

PYTHON

# Method 1: .isdigit() — check before converting
raw = input("Enter your age: ")
if raw.isdigit():
    age = int(raw)
    print(f"You are {age} years old.")
else:
    print("Please enter a valid whole number.")

# Method 2: try/except — handle errors gracefully
try:
    price = float(input("Enter price: "))
    print(f"Price: PKR {price:,.2f}")
except ValueError:
    print("Invalid! Please enter a number like 9.99")

# Method 3: strip() + check empty — common pattern
username = input("Enter username: ").strip()
if username:                   # truthy — non-empty string
    print(f"Welcome, @{username.lower()}!")
else:
    print("Username cannot be empty.")

✨

Always .strip() text input

Users often accidentally add spaces before or after their input. input("Name: ").strip() removes leading/trailing whitespace so " Ali " becomes "Ali". Make it a habit for all text input — it prevents dozens of subtle bugs like failed string comparisons.

Section 5

Building Interactive Programs

Combining print(), input(), variables, operators, and f-strings is all you need to build real interactive console programs. Let's look at three complete examples.

Example 1 — BMI Calculator

bmi_calculator.py

PYTHON

# ── BMI Calculator ───────────────────────────
print("=" * 35)
print("      BMI CALCULATOR")
print("=" * 35)

name   = input("Enter your name  : ").strip().title()
weight = float(input("Weight (kg)      : "))
height = float(input("Height (m)       : "))

bmi = weight / (height ** 2)

if bmi < 18.5:
    category = "Underweight"
elif bmi < 25:
    category = "Normal weight"
elif bmi < 30:
    category = "Overweight"
else:
    category = "Obese"

print(f"""
─────────────────────────────────
  Result for: {name}
  BMI      : {bmi:.2f}
  Category : {category}
─────────────────────────────────""")

Example 2 — Currency Converter

currency_converter.py

PYTHON

# ── Currency Converter ───────────────────────
USD_TO_PKR = 278.50   # constant (rate)
USD_TO_GBP = 0.79
USD_TO_EUR = 0.92

print("Currency Converter (USD base)")
print("-" * 30)

amount = float(input("Enter amount in USD: $"))

print(f"""
  ${amount:.2f} USD equals:
  PKR {amount * USD_TO_PKR:,.2f}
  GBP {amount * USD_TO_GBP:.2f}
  EUR {amount * USD_TO_EUR:.2f}""")

📋

Pattern: Prompt → Validate → Convert → Use

Every interactive program follows: show prompt → get string → validate → convert type → compute → output. Internalise this flow and you can build anything.

🎨

Make output scannable

Use "=" * 30 for headers, "-" * 30 for dividers, aligned columns with f-string width formatting. Good output UX makes programs feel professional.

⌨️

Prompt text matters

Always tell the user what format you expect: "Enter height in metres (e.g. 1.75): " is far better than just "Height: ". Clear prompts reduce bad input.

🔒

Never trust raw input

Strip whitespace, check for empty strings, and use try/except around conversions. This is the foundation of defensive programming.

🧩 Knowledge Check

5 questions — test your mastery of Input & Output

1. What type does input() always return?

2. What does print("a", "b", "c", sep="-") output?

3. A user types 25 at an input() prompt. You then write age + 5. What happens?

4. What does print("Hi", end="") do differently from a normal print("Hi")?

5. Which line collects two integers from a single line of user input (e.g. user types 10 20)?

🏗️

Coding Challenge — Personal Finance Tracker

A complete interactive console app using everything from Phase 1

Task: Build a Personal Finance Tracker that:

1. Asks for the user's name (strip + title case it)
2. Asks for their monthly income (float)
3. Collects 3 expense amounts in a single input line (e.g. 8000 3500 2000) using map(float, ...split())
4. Calculates total expenses, savings, and savings rate %
5. Uses a comparison + logical operator to check if savings rate is healthy (≥ 20% AND savings > 0)
6. Prints a formatted report card with currency formatting (:,.2f) and a percentage (:.1f)
7. Prints a tip based on whether savings rate is healthy

💡 Show hints

Use e1, e2, e3 = map(float, input("Expenses: ").split())
Savings rate: (savings / income) * 100
Healthy check: rate >= 20 and savings > 0
Currency: f"PKR {income:,.2f}"

finance_tracker.py — Sample Solution

PYTHON

# ── Personal Finance Tracker ─────────────────
name   = input("Your name       : ").strip().title()
income = float(input("Monthly income  : "))

print("Enter 3 expenses separated by spaces:")
e1, e2, e3 = map(float, input("Expenses        : ").split())

total_exp   = e1 + e2 + e3
savings     = income - total_exp
savings_pct = (savings / income) * 100
is_healthy  = savings_pct >= 20 and savings > 0

tip = "✅ Great discipline! Keep saving." if is_healthy else "⚠️ Try to cut expenses and save ≥20%."

print(f"""
╔═══════════════════════════════════╗
  Finance Report — {name}
  ───────────────────────────────────
  Income       : PKR {income:,.2f}
  Expense 1    : PKR {e1:,.2f}
  Expense 2    : PKR {e2:,.2f}
  Expense 3    : PKR {e3:,.2f}
  ───────────────────────────────────
  Total Exp    : PKR {total_exp:,.2f}
  Savings      : PKR {savings:,.2f}
  Savings Rate : {savings_pct:.1f}%
  Healthy      : {is_healthy}
  ───────────────────────────────────
  Tip: {tip}
╚═══════════════════════════════════╝""")

Phase 1 · FoundationsLesson 5 of 6

Input & Output

print() — In Depth

Number Formatting in print()

input() — Getting User Data

Multiple Inputs & split()

Input Validation

Building Interactive Programs

Example 1 — BMI Calculator

Example 2 — Currency Converter

`print()` — In Depth

`input()` — Getting User Data