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Courses/Python Mastery/The Building Blocks (Tokens & Syntax)

Keywords — The 35 Reserved Words

20 min • Beginner • Module 2

The words Python has reserved for itself: if, for, def, class, True, False — what each one does.

Keywords — The 35 Reserved Words

Keywords are the words Python owns. They define the language itself — you cannot use them as variable names, no matter how clever the idea seems.

See them all yourself

Python can list its keywords for you:

import keyword
print(keyword.kwlist)
print(len(keyword.kwlist))

Output (Python 3.12):

['False', 'None', 'True', 'and', 'as', 'assert', 'async', 'await', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'nonlocal', 'not', 'or', 'pass', 'raise', 'return', 'try', 'while', 'with', 'yield']
35

Thirty-five words. That’s the entire “vocabulary” Python reserves — English has hundreds of thousands. This smallness is a feature: you can learn every keyword in a week.

The proof they’re reserved

Try to use one as a variable:

for = 5

Output:

SyntaxError: invalid syntax

Python stops you instantly. Compare with a non-keyword:

for_you = 5      # fine — "for_you" is not the keyword "for"

The keywords, grouped by what they do

Values: True, False, None

Decisions: if, elif, else

Loops: for, while, break, continue

Functions: def, return, lambda, yield, pass, global, nonlocal

Classes & objects: class, self-adjacent tools like del

Logic: and, or, not, in, is

Errors: try, except, finally, raise, assert

Imports: import, from, as

Contexts: with, async, await

You already know some from Module 1. The rest arrive naturally, one per lesson — by the end of this course you’ll have used almost all 35 without ever sitting down to “memorize keywords.”

The three special-value keywords (meet them now)

True, False, and None appear constantly:

is_student = True
is_teacher = False
result = None          # "nothing yet" — an empty placeholder

None deserves special attention: it means “no value here”, and it’s what functions return when they don’t return anything:

def say_hi():
    print("hi")

x = say_hi()
print(x)        # None — say_hi displays text but returns nothing

Common Errors & Fixes

  • SyntaxError: invalid syntax on a line that looks fine — check if you used a keyword as a name (class = "10th", for = 5).
  • NameError: name 'true' is not defined — Python keywords are case-sensitive: it’s True, not true. Same for False and None. This one catches everyone coming from other languages.
  • SyntaxError: cannot assign to True — trying to change a keyword’s value. They’re reserved; pick another name.

✅ Checkpoint

  1. How many keywords does Python have, and how could you list them yourself? (35 — import keyword; print(keyword.kwlist))
  2. Which is valid: import = 5 or importing = 5? (importing — “importing” is not the keyword “import”)
  3. What does None mean? (No value — an intentional empty placeholder)
  4. Is it true or True? (True — keywords are case-sensitive)

Next: identifiers — the names you get to invent, and the rules that govern them.