Identifiers and Reserved Words

Identifiers

An identifier is the name given to variables, functions, classes, and modules.

Rules for naming identifiers:

1. Can contain letters (a–z, A–Z), digits (0–9), and underscore (_).
2. Must not start with a digit.
3. Cannot be a Python reserved keyword.
4. Case-sensitive (total ≠ Total).
5. No spaces or special characters (@, $, %, etc.) allowed.

# Valid identifiers
name = "Riya"
_age = 20
student1 = "BCA"
total_marks = 450

# Invalid identifiers (would raise SyntaxError)
# 1student = "BCA"     -> starts with digit
# total-marks = 450    -> hyphen not allowed
# class = "python"     -> 'class' is a reserved keyword

Naming conventions (PEP 8):

• Variables & functions: snake_case (total_marks)
• Classes: PascalCase (StudentRecord)
• Constants: UPPER_CASE (MAX_LIMIT)
• Private members: leading underscore (_internal)

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Reserved Words (Keywords)

Reserved words are predefined words with special meaning; they cannot be used as identifiers. Python 3 has 35 keywords:

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

import keyword
print(keyword.kwlist)     # prints the full list of keywords
print(len(keyword.kwlist))
print(keyword.iskeyword("for"))    # True
print(keyword.iskeyword("value"))  # False