Python Inputs Tutorial 2026 – input(), Validation & CLI | Poetic Bytes

def basic_input_demo():
    name = input("What is your name? ")
    print(f"Hello, {name}! Nice to meet you.")

    age = input("How old are you? ")
    print(f"You are {age} years old.")
    print(f"Type of age: {type(age)}")

basic_input_demo()

def multi_line_prompt():
    prompt = """
    ─── Welcome to the Calculator ───
    Enter two numbers and an operation.
    """
    print(prompt)

    a = input("First number: ")
    b = input("Second number: ")
    op = input("Operation (+, -, *, /): ")

    print(f"Inputs: {a} {op} {b}")

multi_line_prompt()

def handle_empty():
    response = input("Type something (or press Enter): ")

    if response == "":
        print("You pressed Enter without typing anything!")
    else:
        print(f"You typed: {response}")

    print(f"Length: {len(response)} characters")

handle_empty()

def int_conversion_demo():
    age_str = input("Enter your age: ")
    age = int(age_str)

    print(f"Next year you will be {age + 1}")
    print(f"Type of age: {type(age)}")

    binary = "1010"
    decimal = int(binary, base=2)
    print(f"Binary {binary} = decimal {decimal}")

int_conversion_demo()

def float_conversion_demo():
    price_str = input("Enter the price: $")
    price = float(price_str)

    tax = price * 0.08
    total = price + tax

    print(f"Price: ${price:.2f}")
    print(f"Tax (8%): ${tax:.2f}")
    print(f"Total: ${total:.2f}")
    print(f"Type of price: {type(price)}")

float_conversion_demo()

def bool_conversion_demo():
    user_input = input("Enter something: ")
    value = bool(user_input)

    print(f"bool('{user_input}') = {value}")

    if value:
        print("You entered something non-empty!")
    else:
        print("You entered nothing.")

    print(f"bool(0) = {bool(0)}")
    print(f"bool(42) = {bool(42)}")
    print(f"bool('yes') = {bool('yes')}")

bool_conversion_demo()

def validate_integer():
    try:
        value = int(input("Enter a whole number: "))
        print(f"✅ You entered: {value}")
        return value
    except ValueError:
        print("❌ That's not a valid whole number!")
        return None

result = validate_integer()
if result is not None:
    print(f"Double it: {result * 2}")

def get_positive_number(prompt: str) -> float:
    while True:
        try:
            value = float(input(prompt))
            if value > 0:
                return value
            print("❌ Please enter a positive number.")
        except ValueError:
            print("❌ Invalid input. Please enter a number.")

def main():
    radius = get_positive_number("Enter radius: ")
    area = 3.14159 * radius ** 2
    print(f"✅ Area of circle: {area:.2f}")

main()

def get_score() -> int:
    while True:
        try:
            score = int(input("Enter a score (0–100): "))
            if 0 <= score <= 100:
                return score
            print("❌ Score must be between 0 and 100.")
        except ValueError:
            print("❌ Please enter a whole number.")

def grade_score(score: int) -> str:
    if score >= 90: return "A"
    if score >= 80: return "B"
    if score >= 70: return "C"
    if score >= 60: return "D"
    return "F"

score = get_score()
print(f"✅ Score {score} → Grade {grade_score(score)}")

import re

def validate_name() -> str:
    while True:
        name = input("Enter your name (2–30 letters): ").strip()

        if len(name) < 2 or len(name) > 30:
            print("❌ Name must be 2–30 characters.")
            continue

        if not re.match(r"^[A-Za-z\s\-'']+$", name):
            print("❌ Name contains invalid characters.")
            continue

        return name

def validate_email() -> str:
    while True:
        email = input("Enter your email: ").strip()
        if re.match(r"^[\w\.-]+@[\w\.-]+\.\w+$", email):
            return email
        print("❌ Invalid email format.")

name = validate_name()
email = validate_email()
print(f"✅ Welcome, {name}! Email: {email}")

def parse_multiple_numbers():
    raw = input("Enter three numbers separated by spaces: ")
    parts = raw.split()
    print(f"Parts: {parts}")

    if len(parts) != 3:
        print("❌ Please enter exactly three numbers.")
        return

    try:
        a, b, c = float(parts[0]), float(parts[1]), float(parts[2])
        print(f"✅ Sum: {a + b + c:.2f}")
        print(f"✅ Average: {(a + b + c) / 3:.2f}")
    except ValueError:
        print("❌ All inputs must be numbers.")

parse_multiple_numbers()

def collect_items() -> list:
    items = []
    print("Enter items one per line. Press Enter twice to finish.")

    while True:
        line = input("> ")
        if line == "":
            break
        items.append(line)

    return items

def main():
    items = collect_items()
    print(f"\nYou entered {len(items)} items:")
    for i, item in enumerate(items, 1):
        print(f"  {i}. {item}")

main()

import sys

def show_argv():
    print(f"Script name: {sys.argv[0]}")
    print(f"Number of arguments: {len(sys.argv) - 1}")

    for i, arg in enumerate(sys.argv[1:], 1):
        print(f"  Arg {i}: {arg}")

    if len(sys.argv) > 1:
        print(f"\nFirst argument: {sys.argv[1]}")

show_argv()

import sys

def simple_cli():
    if len(sys.argv) < 2:
        print("Usage: python script.py <name> [age]")
        return

    name = sys.argv[1]
    age = "unknown"

    if len(sys.argv) >= 3:
        try:
            age = int(sys.argv[2])
        except ValueError:
            age = "invalid"

    print(f"Hello, {name}!")
    print(f"Age: {age}")

simple_cli()

import argparse

def build_parser():
    parser = argparse.ArgumentParser(
        description="A simple CLI tool with argparse"
    )

    parser.add_argument("name", help="Your name")
    parser.add_argument("--age", type=int, default=18, help="Your age (default: 18)")
    parser.add_argument("--verbose", action="store_true", help="Enable verbose output")

    return parser

def main():
    parser = build_parser()
    args = parser.parse_args(["Alice", "--age", "25", "--verbose"])

    if args.verbose:
        print("🔍 Verbose mode enabled")

    print(f"Hello, {args.name}!")
    print(f"Age: {args.age}")

    if args.age >= 18:
        print("✅ You are an adult.")
    else:
        print("🔞 You are a minor.")

main()

import argparse

def create_parser():
    parser = argparse.ArgumentParser(description="File operations")

    parser.add_argument("source", help="Source file path")
    parser.add_argument("dest", nargs="?", default=".", help="Destination path (default: current dir)")

    parser.add_argument("-v", "--verbose", action="store_true", help="Verbose output")
    parser.add_argument("-f", "--force", action="store_true", help="Overwrite without asking")

    return parser

def main():
    parser = create_parser()
    args = parser.parse_args(["report.txt", "/backup/", "--verbose"])

    print(f"Source: {args.source}")
    print(f"Destination: {args.dest}")
    print(f"Verbose: {args.verbose}")
    print(f"Force: {args.force}")

main()

import getpass

def secure_login():
    username = input("Username: ")
    password = getpass.getpass("Password: ")

    print(f"\nUsername: {username}")
    print(f"Password length: {len(password)} characters (hidden)")

    if username == "admin" and password == "secret123":
        print("✅ Login successful!")
    else:
        print("❌ Invalid credentials.")

secure_login()

import getpass

def change_password():
    print("🔐 Change Password")
    print("-" * 30)

    current = getpass.getpass("Current password: ")
    if current != "secret123":
        print("❌ Incorrect current password.")
        return

    new1 = getpass.getpass("New password: ")
    new2 = getpass.getpass("Confirm new password: ")

    if new1 != new2:
        print("❌ Passwords do not match.")
        return

    if len(new1) < 8:
        print("❌ Password must be at least 8 characters.")
        return

    print("✅ Password changed successfully!")

change_password()

def read_text_file(path: str):
    try:
        with open(path, "r", encoding="utf-8") as f:
            content = f.read()
            print(f"📄 File: {path}")
            print(f"Characters: {len(content)}")
            print("Content:")
            print(content[:200])
    except FileNotFoundError:
        print(f"❌ File not found: {path}")
    except Exception as e:
        print(f"❌ Error reading file: {e}")

read_text_file("sample.txt")

import csv
from io import StringIO

def parse_csv_data(csv_text: str):
    reader = csv.DictReader(StringIO(csv_text))
    rows = list(reader)

    print(f"📊 Found {len(rows)} rows")
    if rows:
        print(f"Columns: {', '.join(rows[0].keys())}")
        for row in rows[:3]:
            print(row)

csv_sample = """name,age,city
Alice,30,New York
Bob,25,London
Charlie,35,Paris"""

parse_csv_data(csv_sample)

import json

json_sample = '{"user": "glenn", "level": "advanced", "scores": [95, 88, 92]}'

def parse_json(data: str):
    try:
        obj = json.loads(data)
        print("✅ JSON parsed successfully")
        print(f"User: {obj['user']}")
        print(f"Level: {obj['level']}")
        print(f"Scores: {obj['scores']}")
        print(f"Average: {sum(obj['scores']) / len(obj['scores']):.1f}")
    except json.JSONDecodeError as e:
        print(f"❌ Invalid JSON: {e}")

parse_json(json_sample)

def sentinel_loop():
    total = 0
    count = 0
    print("Enter numbers to sum. Type 'quit' to stop.")

    while True:
        raw = input("> ")
        if raw.lower() == "quit":
            break

        try:
            num = float(raw)
            total += num
            count += 1
            print(f"✅ Added {num}. Running total: {total:.2f}")
        except ValueError:
            print("❌ Invalid number. Try again.")

    if count > 0:
        print(f"📊 Summary: {count} numbers, total {total:.2f}, average {total/count:.2f}")
    else:
        print("No numbers entered.")

sentinel_loop()

def show_menu():
    print("\n📋 Menu")
    print("  1. Say hello")
    print("  2. Double a number")
    print("  3. Show current time")
    print("  0. Exit")

def menu_loop():
    while True:
        show_menu()
        choice = input("Choose an option: ").strip()

        if choice == "0":
            print("👋 Goodbye!")
            break
        elif choice == "1":
            name = input("Your name: ")
            print(f"Hello, {name}! 👋")
        elif choice == "2":
            try:
                num = float(input("Enter a number: "))
                print(f"Double: {num * 2}")
            except ValueError:
                print("❌ Invalid number.")
        elif choice == "3":
            import time
            print(f"🕐 {time.strftime('%H:%M:%S')}")
        else:
            print("❌ Invalid option. Try again.")

menu_loop()

from typing import Optional

def safe_int_input(
    prompt: str,
    min_val: Optional[int] = None,
    max_val: Optional[int] = None,
    retries: int = 3
) -> Optional[int]:
    for attempt in range(1, retries + 1):
        try:
            raw = input(f"{prompt} ")
            value = int(raw)

            if min_val is not None and value < min_val:
                print(f"❌ Value must be at least {min_val}.")
                continue

            if max_val is not None and value > max_val:
                print(f"❌ Value must be at most {max_val}.")
                continue

            return value

        except ValueError:
            print(f"❌ Invalid integer. ({retries - attempt} attempts left)")

    print("❌ Too many attempts. Returning None.")
    return None

age = safe_int_input("Enter your age:", min_val=1, max_val=120)
if age is not None:
    print(f"✅ Age: {age}")

score = safe_int_input("Enter a score (0-100):", min_val=0, max_val=100)
if score is not None:
    print(f"✅ Score: {score}")

def read_file_safely(path: str):
    try:
        with open(path, "r", encoding="utf-8") as f:
            return f.read()
    except FileNotFoundError:
        print(f"❌ File not found: {path}")
        return None
    except PermissionError:
        print(f"❌ Permission denied: {path}")
        return None
    except UnicodeDecodeError as e:
        print(f"❌ Encoding error: {e}")
        return None
    except Exception as e:
        print(f"❌ Unexpected error: {e}")
        return None

content = read_file_safely("sample.txt")
if content is not None:
    print(f"✅ Read {len(content)} characters")

import json
from pathlib import Path

def interactive_config() -> dict:
    print("\n⚙️ Interactive Configuration Setup")
    print("Press Enter to use default values.")

    config = {}

    name = input("Project name [default: myproject]: ") or "myproject"
    config["name"] = name

    port_input = input("Port [default: 8000]: ")
    config["port"] = int(port_input) if port_input else 8000

    debug_input = input("Debug mode? (yes/no) [default: no]: ")
    config["debug"] = debug_input.lower() in ("yes", "y", "true")

    env = input("Environment [dev/prod, default: dev]: ") or "dev"
    config["environment"] = env

    return config

def save_config(config: dict, path: str = "config.json"):
    with open(path, "w", encoding="utf-8") as f:
        json.dump(config, f, indent=2)
    print(f"✅ Config saved to {path}")

config = interactive_config()
print("\n📋 Configuration:")
for k, v in config.items():
    print(f"  {k}: {v}")

import re

def collect_person_data() -> dict:
    print("\n📝 Enter person details:")

    while True:
        name = input("Full name: ").strip()
        if len(name) >= 2 and re.match(r"^[A-Za-z\s\-'']+$", name):
            break
        print("❌ Please enter a valid name (2+ letters, no numbers).")

    while True:
        email = input("Email: ").strip()
        if re.match(r"^[\w\.-]+@[\w\.-]+\.\w+$", email):
            break
        print("❌ Invalid email format.")

    while True:
        age_str = input("Age: ")
        try:
            age = int(age_str)
            if 1 <= age <= 150:
                break
            print("❌ Age must be between 1 and 150.")
        except ValueError:
            print("❌ Please enter a valid number.")

    role = input("Role (developer, designer, manager): ").strip().lower()
    if role not in ("developer", "designer", "manager"):
        role = "other"
        print(f"Role set to {role}")

    return {"name": name, "email": email, "age": age, "role": role}

person = collect_person_data()
print("\n✅ Person saved:")
for k, v in person.items():
    print(f"  {k}: {v}")

import argparse

def build_subcommand_parser():
    parser = argparse.ArgumentParser(description="Task manager CLI")
    subparsers = parser.add_subparsers(dest="command", required=True)

    add_parser = subparsers.add_parser("add", help="Add a task")
    add_parser.add_argument("title", help="Task title")
    add_parser.add_argument("--priority", choices=["low", "medium", "high"], default="medium")

    list_parser = subparsers.add_parser("list", help="List tasks")
    list_parser.add_argument("--filter", choices=["all", "active", "done"], default="all")

    done_parser = subparsers.add_parser("done", help="Mark task as done")
    done_parser.add_argument("task_id", type=int, help="Task ID")

    return parser

def main():
    parser = build_subcommand_parser()
    args = parser.parse_args(["add", "Buy milk", "--priority", "high"])

    if args.command == "add":
        print(f"✅ Added task: '{args.title}' (priority: {args.priority})")
    elif args.command == "list":
        print(f"📋 Listing tasks (filter: {args.filter})")
    elif args.command == "done":
        print(f"✅ Task {args.task_id} marked as done")

main()