User Input and Output

# User Input and Output

Welcome to Chapter 6! So far, our programs have used hardcoded values. Now it's time to make them interactive by accepting input from users.

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1. Introduction #

Real-world programs interact with users. A login form asks for credentials. A calculator asks for numbers. In Python, the input() function makes this possible.

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2. Learning Objectives #

• Use the input() function to get user input.

• Convert input to appropriate data types.

• Format output using f-strings, .format(), and % operator.

• Use escape characters and raw strings.

• Build a user profile generator.

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3. The input() Function #

```python id="py6_ex1" name = input("Enter your name: ") print(f"Hello, {name}!")

**Important:** `input()` always returns a **string**:

python id="py6_ex2" age = int(input("Enter your age: ")) height = float(input("Enter height (m): ")) print(f"Age: {age}, Height: {height}")

### Multiple Inputs

python id="py6_ex3" a, b = map(int, input("Enter two numbers: ").split()) print(f"Sum: {a + b}")

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## 4. f-Strings (Python 3.6+)

python id="py6_ex4" name = "Alice" age = 25 gpa = 3.856

print(f"Name: {name}, Age: {age}") print(f"GPA: {gpa:.2f}") print(f"Formatted: {1234567:,}") print(f"Percentage: {0.856:.1%}") print(f"{'Left':<15}|{'Center':^15}|{'Right':>15}|") print(f"Padded: {42:05d}")

### .format() Method

python id="py6_ex5" print("Hello, {}! Age: {}".format("Bob", 30)) print("{name} is {age}".format(name="Alice", age=25))

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## 5. Escape Characters

| Escape | Meaning |
|--------|---------|
| `\n` | New line |
| `\t` | Tab |
| `\\` | Backslash |
| `\"` | Double quote |

python id="py6_ex6" print("Line 1\nLine 2") print("Name\tAge") path = r"C:\Users\folder" # Raw string print(path)

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## 6. Mini Project: User Profile Generator

python id="py6project" print("=" * 50) print(" 👤 USER PROFILE GENERATOR") print("=" * 50)

firstname = input(" First name: ") lastname = input(" Last name: ") age = int(input(" Age: ")) email = input(" Email: ") city = input(" City: ")

username = f"{firstname.lower()}.{lastname.lower()}{age}"

print("\n" + "=" * 50) print(f"{'GENERATED PROFILE':^50}") print("=" * 50) print(f" {'Full Name':<15}: {firstname} {last_name}") print(f" {'Username':<15}: {username}") print(f" {'Age':<15}: {age}") print(f" {'Email':<15}: {email}") print(f" {'City':<15}: {city}") print(f" {'Status':<15}: {'Minor 🔒' if age < 18 else 'Adult ✅'}") print("=" * 50)

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## 7. Practical Example: Formatted Receipt

python id="py6ex7" print(f"{'STORE RECEIPT':^40}") print("=" * 40)

for name, qty, price in items: linetotal = qty * price total += linetotal print(f"{name:<15}{qty:>5}${price:>9.2f}${linetotal:>9.2f}")

print("-" * 40) print(f"{'GRAND TOTAL':>30}${total:>9.2f}") ``

1. 1. Forgetting to convert input: input() returns strings. Use int() or float().

1. 2. Forgetting the f prefix: "{name}" prints literally, not the variable value.

1. 3. Not handling invalid input: int("abc") crashes with ValueError.

1. 4. Escape characters in paths: Use raw strings r"C:\path".

• Use .strip() to remove whitespace: input("Name: ").strip().

Q1: input() returns: A) int B) float C) str D) depends Answer: C

Q2: How to get integer input? A) input(int) B) int(input()) C) input().int() D) integer(input()) Answer: B

Q3: :.2f in f-string does: A) Rounds to 2 ints B) 2 decimal places C) Pads 2 zeros D) Multiplies by 2 Answer: B

Q5: f"{'hi':>10}" produces: A) hi-------- B) --------hi C) ----hi---- D) hi Answer: B

Q6: split() does: A) Joins B) Splits to list C) Removes chars D) Converts case Answer: B

Q7: int("abc") causes: A) Returns 0 B) Returns None C) ValueError D) Returns "abc" Answer: C

Q8: \t produces: A) New line B) Tab C) Backspace D) Alert Answer: B

1. 1. Difference between input() in Python 2 vs 3? Python 3 input() always returns string. Python 2 input() evaluates the expression.

1. 4. Difference between print() and return? print() outputs to console; return sends value back from function.

1. 5. What are raw strings? Strings prefixed with r that treat backslashes as literal characters.

Q: Can f-strings contain conditions? A: Yes! f"{'pass' if score >= 60 else 'fail'}" works.

Q: How to read from file instead of keyboard? A: File handling (Chapter 16) or redirect: python script.py < input.txt.

• input() returns strings; convert with int(), float().

In Chapter 7: Conditional Statements, you'll learn decision-making with if, elif, else`, and build a grade calculator! 🚀