Python — User Input

input() — pause and ask

name = input("What's your name? ")
print(f"Hello, {name}!")

The program halts, shows the prompt, waits for Enter, returns everything typed as a string — always.

The conversion rule (again, because it matters)

age = input("Age? ")        # "25" even if user typed digits
age + 1                     # TypeError!

age = int(input("Age? "))   # convert at the door ✓

Floats:

price = float(input("Price? "))

Validation loop — never trust input

while True:
    raw = input("Age: ")
    if raw.isdigit():
        age = int(raw)
        break
    print("Numbers only, please.")

Or the try/except flavor (handles negatives too):

while True:
    try:
        age = int(input("Age: "))
        if 0 <= age <= 130:
            break
        print("Enter a realistic age.")
    except ValueError:
        print("Not a number.")

Multi-line prompts & defaults

answer = input("""Choose:
  1) Start
  2) Settings
> """).strip()          # .strip() forgives stray spaces
if not answer:
    answer = "1"        # default on empty Enter

.strip() + .lower() normalize almost every messy input:

if input("Proceed? y/n ").strip().lower().startswith("y"):
    start()

Multiple values in one line

x, y = input("Two numbers separated by space: ").split()
x, y = int(x), int(y)

# or list comprehension:
nums = [int(n) for n in input("Numbers: ").split()]
sum(nums)

split() without arguments splits on any run of whitespace.

Passwords — no echo

import getpass
password = getpass.getpass("Password: ")   # typed chars hidden

Never input() for secrets; terminals echo everything.

Interactive menu skeleton

items = []

while True:
    cmd = input("[a]dd [l]ist [q]uit > ").strip().lower()

    if cmd in ("q", "quit"):
        break
    elif cmd in ("a", "add"):
        items.append(input("New item: "))
    elif cmd in ("l", "list"):
        print("\n".join(items) or "(empty)")
    else:
        print("Unknown command")

This while-True/dispatch shape powers every console tool you'll build early on.

Gotchas: trailing \n is NOT included in input()'s result · EOF (Ctrl+D/Ctrl+Z) raises EOFError — wrap long-running tools' input calls when piping data.

Mini Practice

1. Greeter asking name + birth year → prints age.
2. Bulletproof float input for a price.
3. y/n confirm helper function returning bool.
4. Two-number calculator reading both from one line.
5. Full add/list/quit todo menu.

Next: string formatting →