Python Keywords, Identifiers & Variables

📚 What You'll Learn Here

Python Keywords — Reserved words and their purpose
Python Identifiers — Naming rules and conventions
Python Variables — How to store and manage data
Rules for Naming — What's valid and what's not
Variables vs Identifiers — Understanding the difference
Hands-on Practice — Write and run Python code
Interactive Quiz — Test your knowledge

1. Python Keywords — The Reserved Words

Keywords are unique reserved words in Python that cannot be used as variable names, function names, or other identifiers. They are the building blocks of the Python language — the vocabulary that Python understands.

Each keyword serves a specific purpose, and together they form the syntax of Python programs. As of Python 3.11.2, there are 35 keywords that Python supports.

💡 Important: All keywords in Python are case-sensitive. So IF is not the same as if. Be careful when using them!

List of Python Keywords:

All 35 Python Keywords:

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

How to List All Keywords:

# Python script to list all keywords
import keyword
print(keyword.kwlist)

Output:
['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']

Using help() to View Keywords:

>>> help("keywords")

Here is a list of the Python keywords. Enter any keyword to get more help.

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

📝 Note: The list of Python keywords may change in future releases. New keywords may be added, and old ones may be discontinued.

2. Python Identifiers — Naming Your Code

Identifiers are the names given to entities like variables, functions, classes, and labels in a program. When you assign a name to a programmable entity in Python, it's technically called an identifier.

Identifiers must be different from keywords. Keywords cannot be used as identifiers. Python has a set of rules for creating meaningful identifiers.

Rules for Naming Identifiers:

Use letters, digits, or underscores: Combination of alphabets (a-z, A-Z), digits (0-9), or underscore (_)
Cannot start with a digit: Digits cannot be used as the first character
Cannot use keywords: Keywords are reserved and cannot be used as identifiers
No special symbols: Symbols like !, @, #, $, %, etc. are not allowed
Case-sensitive: myVar and myvar are different

✅ Valid Identifiers

shapeClass
shape_1
upload_shape_to_db
_private
myVar123

❌ Invalid Identifiers

1shape (starts with digit)
shape class (has space)
class (is a keyword)
my-var (has hyphen)
@name (has special symbol)

# Valid identifiers
>>> shapeClass = 1
✅ Works fine!

# Invalid identifiers (will raise errors)
>>> shape Class = 1
SyntaxError: invalid syntax

>>> 1shape = 1
SyntaxError: invalid decimal literal

3. Python Variables — Storing Your Data

Variables are names that refer to memory locations where data is stored. They are the most fundamental concept in programming — they allow you to store, retrieve, and manipulate data.

Key Facts About Python Variables:

📌 No Declaration Needed

Variables don't require explicit declaration. You just assign a value and the variable is created.

🔄 Dynamic Typing

Variables can hold different types of objects at different times. They are references to objects, not the objects themselves.

🧠 Object-Oriented

Every variable points to an object that has a type, value, and reference count.

Understanding Python Variables:

# Variable assignment and type checking
>>> age = 20
>>> type(age)
<class 'int'>

>>> name = 'Python'
>>> type(name)
<class 'str'>

>>> name = {'Python', 'C', 'C++'}
>>> type(name)
<class 'set'>

How Variables Work in Python:

Creation: When you assign a value, Python creates an object in memory
Reference: The variable name becomes a reference to that object
Rebinding: When the value changes, Python creates a new object and updates the reference
Garbage Collection: Old objects are automatically cleaned up when no longer referenced

# Memory address changes when value changes
>>> age = 20
>>> id(age)
1716585200

>>> age = 11
>>> id(age)
1716585232
# Different memory address = new object!

4. Rules for Naming Python Variables

✅ Legal Variable Names

myname = "Python"
my_name = "Python"
_my_name = "Python"
myName = "Python"
MYNAME = "Python"
myname2 = "Python"

❌ Illegal Variable Names

2myname = "Python" (starts with digit)
my-name = "Python" (has hyphen)
my var = "Python" (has space)

# ✅ Valid variable names
myname = "Python"
my_name = "Python"
_my_name = "Python"
myName = "Python"
MYNAME = "Python"
myname2 = "Python"

# ❌ Invalid variable names (will raise errors)
2myname = "Python"    # SyntaxError
my-name = "Python"    # SyntaxError
my var = "Python"     # SyntaxError

5. Variables vs Identifiers — What's the Difference?

Variables	Identifiers
A variable is a unique name given to a memory location	A unique name given to any entity is called an identifier
Variable names are called identifiers	The range of identifiers is higher than variables
A variable is a name given to a memory location that holds some kind of value	An identifier is a name given to variables, constants, lists, tuples, classes, etc.

💡 Simple way to remember: All variables are identifiers, but not all identifiers are variables! Identifiers are the general term for any named entity in Python.

Try It Yourself!

Now it's your turn! Write and run Python code directly in your browser:

Loading Pyodide... 0%

Python Code Editor

# 🔤 Exploring Python Keywords, Identifiers & Variables

# 1. Keywords - Python's reserved words
import keyword
print("🔑 Python Keywords:")
print(keyword.kwlist)
print()

# 2. Identifiers - Naming your code
# Valid identifiers
my_name = "Python Learner"
my_age = 25
_private = "This is private"
print(f"Name: {my_name}")
print(f"Age: {my_age}")
print(f"Private: {_private}")
print()

# 3. Variables - Storing data
name = "Python"          # String variable
version = 3.11           # Float variable
is_popular = True        # Boolean variable
numbers = [1, 2, 3, 4]   # List variable

print(f"Language: {name}")
print(f"Version: {version}")
print(f"Is Popular? {is_popular}")
print(f"Numbers: {numbers}")
print()

# 4. Dynamic typing - Variables can change type
x = 10       # Integer
print(f"x is {x} (type: {type(x).__name__})")
x = "Hello"  # Now a string
print(f"x is {x} (type: {type(x).__name__})")
x = 3.14     # Now a float
print(f"x is {x} (type: {type(x).__name__})")

# 5. Memory addresses change when value changes
age = 20
print(f"age = {age}, id: {id(age)}")
age = 21
print(f"age = {age}, id: {id(age)}")

print("\n✅ Experiment with your own variables!")

🔑 Python 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']

Name: Python Learner
Age: 25
Private: This is private

Language: Python
Version: 3.11
Is Popular? True
Numbers: [1, 2, 3, 4]

x is 10 (type: int)
x is Hello (type: str)
x is 3.14 (type: float)

age = 20, id: 1716585200
age = 21, id: 1716585232

✅ Experiment with your own variables!

🎯 Challenge Yourself!
• Create a variable with your favorite programming language
• Try creating an invalid identifier and see the error
• Check the type of different variables using type()

🏆

🎉 You've Mastered Python Keywords, Identifiers & Variables!

You now understand the naming rules of Python — keywords, identifiers, and variables. These are fundamental to writing clean, correct Python code!

Quick Quiz - Test Your Knowledge

Let's see what you've learned:

1. How many keywords does Python 3.11 have?

A) 30 B) 32 C) 35 D) 40

2. Which of these is a valid identifier in Python?

A) 2myVar B) my-var C) _myVar D) class

3. What happens when you reassign a variable to a different value in Python?

A) The old value is modified B) A new object is created and the variable points to it C) Nothing happens D) The variable is deleted

Frequently Asked Questions

🤔 What is the difference between a keyword and an identifier? ▼

Keywords are reserved words that Python uses for its own syntax — like if, while, and def. You cannot use them as names. Identifiers are names you create for variables, functions, and classes. They follow specific naming rules and cannot be keywords.

💻 Can I use a keyword as a variable name? ▼

No! Keywords are reserved by Python and cannot be used as identifiers. If you try to use a keyword like if or class as a variable name, Python will raise a syntax error. This is why you should always check if a word is a keyword before using it as a name.

🎯 Why are identifiers case-sensitive in Python? ▼

Python treats uppercase and lowercase letters as different characters. So myVar and myvar are two different identifiers. This allows you to create more precise and meaningful names, following the Python convention of using lowercase with underscores for variables (snake_case).

📚 What is the difference between variables and identifiers? ▼

While often used interchangeably, there is a subtle difference. An identifier is the name you give to any entity (variable, function, class, etc.). A variable is a specific type of identifier that refers to a memory location storing data. All variables are identifiers, but not all identifiers are variables (e.g., function names are identifiers but not variables).

📚 Where to Go From Here

Now that you understand Python keywords, identifiers, and variables, here are some related topics to explore:

Python

🐍 Python Keywords, Identifiers & Variables