Hello-Calc: Python Basics

An interactive introduction to Python's core concepts. Learn about variables, see the list of reserved keywords, understand identifier rules, and see how comments work, all in one place.

1. Variables & Calculation

A variable stores a value. Enter two numbers below to see them stored in variables and then added together.

2. Identifier Rules

An identifier is the name you give to a variable, function, etc. It must follow these rules:

  • Can contain letters (a-z, A-Z), numbers (0-9), and underscores (_).
  • Cannot start with a number. (e.g., 1st_num is invalid).
  • Cannot be a keyword. (e.g., for is invalid).
  • Is case-sensitive. (myVar and myvar are different).

3. Python Keywords

Keywords are the reserved words in Python; you can't use them as variable names. Tap a keyword to see its purpose.

4. Practice Questions

Test your understanding of the concepts.

1) Which of the following is a VALID Python variable name (identifier)?
How: user_score_2 follows all rules.
Why the others are wrong: 2nd_place starts with a number. global is a keyword. user-score contains a hyphen, which is not allowed.
2) What is the primary purpose of a comment in code?
How: Comments (starting with # in Python) are ignored by the computer and are meant to provide explanations for humans reading the code.