Important Points about Variables:

• You don't need to declare the variable type in Python.
• The variable's type is determined automatically based on the value assigned.
• Variables make programs flexible and reusable.

Why are Variables Important?

• They store data to be used multiple times.
• They allow for dynamic data manipulation.
• They make code readable and logical.

How to Create a Variable

Just use the assignment operator =:

message = "Enjoying Coding with ShikshaSanchar"
count = 5
pi = 3.14

Rules for Naming Variables

While Python is flexible, it has some rules and best practices for naming variables:

1. Variable names must begin with a letter (a–z, A–Z) or underscore (_)

   _valid = 100

   name = "Devanshi"

   2name = "error"     # ❌ Invalid: starts with a number
   @age = 20           # ❌ Invalid: starts with special character

   Note: In Python, variable names can’t start with a number or special character. Therefore, 2name and @age are invalid and will give an errors.

2. Variable names can only contain letters, digits, and underscores

   my_var1 = 10

   roll_number = 25

   my-var = 20       # ❌ Invalid: contains hyphen
   my var = 100      # ❌ Invalid: contains space

   Note: Python variable names cannot have spaces or hyphens. In the above examples, my-var and my var are invalid and will give an error. Use underscores (_) instead, like my_var.

3. Variable names are case-sensitive

   This means Name and name are considered different.

   Name = "Shiksha"
   name = "Sanchar"
   print("Value of variable Name:", Name)
   print("Value of variable name:", name)

   Output:

   Value of variable Name: Shiksha

   Value of variable name: Sanchar

   In Python, variable names are case-sensitive.Therefore in the above example, Name stores "Shiksha" and name stores "Sanchar". Python prints both separately based on their exact spelling and case.

4. Variable names should not be Python reserved keywords

   Examples of reserved words: if, else, for, True, class, etc.

   class = "Math"    # ❌ Invalid: 'class' is a keyword
   if = 10          # ❌ Invalid: 'if' is a keyword

   Note: In Python, keywords like class and if cannot be used as variable namesbecause they are reserved for special purposes in the language.

5. Variable names should be meaningful

   Use descriptive variable names like total_marks instead of short or unclear ones like tm to make your code more readable and understandable.

   # ✅ Recommended (clear and descriptive)

   total_marks = 480

   # ❌ Not recommended (unclear)
   tm = 480

   Using total_marks makes it clear that the variable stores total marks. In contrast, tm is short and confusing, especially in longer programs.

Common Mistakes Students Make:

• Starting variable names with numbers (e.g., 2value)
• Using special characters like @, $, %, - (e.g., my-name)
• Using spaces between variable names (e.g.,my var)
• Using reserved keywords (e.g., if, while)

Correct vs Incorrect Examples

# ✅ Valid Examples
name = "Peehu"
_student_age = 18
marks1 = 95
    

# ❌ Invalid Examples
1name = "Riya"      # Starts with a digit
stu dent = 21       # Contains space
@marks = 92         # Starts with @ symbol
for = "loop"        # Uses reserved keyword
    

Best Practices for Writing Variables

• Use lowercase letters and underscores for multi-word names (e.g., total_price).
• Avoid short, unclear names (e.g., a, m).
• Use variable names that describe the data being stored.
• Use snake_case (words separated by underscores) as a standard in Python.