Python Tutorial / Build a First Program with Variables, Input and Output

Python variables refer to values, input() reads text and print() displays results. Convert input text to a numeric type before using it in arithmetic, then format the result for the reader.

Distinguish assignment from comments

The assignment operator = associates the result on its right with the name on its left. It does not test mathematical equality. Reassigning a name makes later expressions use the new value. Choose meaningful names and avoid overwriting built-in names such as print, input or list.

amount = 3500
amount = amount + 500
print(amount)  # Display the calculated result

This prints 4000. Text after # is a comment rather than an executed instruction. Comments are most useful when they explain a choice, unit or constraint instead of merely restating the code.

For the relevant APIs and platform requirements, see Build a First Program with Variables, Input and Output documentation.

Run the input and output example

Save the following as input_expense.py and run python input_expense.py in the project environment. Enter lunch at the name prompt and 8000 at the amount prompt.

name = input("name: ").strip()
amount_text = input("amount: ").strip()
amount = int(amount_text)
print(f"{name}: {amount:,} KRW")

The program’s standard output, with the typed input omitted, is:

name: amount: lunch: 8,000 KRW

Follow each value through conversion

The first call reads an expense name and removes surrounding whitespace. amount_text remains a string until int() converts it to an integer. An f-string places expressions inside braces; the comma format specifier displays thousands separators.

A terminal normally echoes what you type, so its interactive line layout will differ from the output-only block above. Input waiting is also normal: a stationary cursor does not necessarily mean the program is stuck.

Change one input and inspect failures

1. Enter 9000 instead of 8000 and check for 9,000 KRW.
2. Enter 8000.5 and observe ValueError because int() does not parse a decimal-point string.
3. Try an empty amount, then restore the valid 8000 input and confirm normal execution.

Track where text becomes a number rather than assuming that a numeric-looking input is already numeric. Handling invalid input and asking again requires a deliberate validation loop; the exception handling lesson explains how to add that behavior without hiding unrelated failures.