What Are Variables in Python?

Variables in Python are used to store data values. They act as labels for data, allowing you to easily reference and manipulate that data throughout your program. Essentially, a variable is a name that points to a value in memory.

Key Characteristics of Variables:

  • Dynamic Typing: You don't need to specify the data type when creating a variable; Python infers it automatically.
  • Mutable: The value stored in a variable can change during program execution.

Rules for Creating Variables in Python:

  1. Naming Rules:
    • Start with a Letter or Underscore:
      • A variable name must begin with an alphabet letter (A-Z, a-z) or an underscore (_).
        • Example: my_var, _var1
    • Followed by Letters, Numbers, or Underscores:
      • After the first character, you can use letters, numbers (0-9), or underscores.
        • Example: var1, var_name2
    • No Special Characters or Spaces:
      • You cannot use symbols like @, #, $, %, etc., and spaces are not allowed.
        • Example: my-var or my var are invalid.
  2. Case Sensitivity:
    • Variable names are case-sensitive. This means myVar and myvar would be treated as different variables.
  3. Reserved Words:
    • You cannot use Python's reserved keywords (like if, for, while, class, etc.) as variable names.
      • Example: class is a reserved word and cannot be used as a variable name.
  4. Length:
    • There is no strict limit on the length of a variable name, but it is recommended to keep it descriptive yet concise.

Examples of Valid and Invalid Variable Names:

  • Valid Names:

    • age
    • user_name
    • totalAmount
    • __init__

  • Invalid Names:

    • 2ndVariable (starts with a number)
    • my-variable (contains a special character)
    • my var (contains a space)
    • class (reserved keyword)

By following these rules, you can create effective and meaningful variable names in your Python programs.

Always remember, Python is a case-sensitive language, meaning that uppercase and lowercase letters are treated as different. So, in Python, variables with the same name but different cases (e.g., Variable, variable, and VARIABLE) are considered distinct and separate. Be careful with this when naming variables or working with code to avoid errors!

Example

age = 20

Age = 30

print(age)
print(Age)

Output:

20
30

=== Code Execution Successful ===

Different Types of Variables

  • Variables can store different types of information:
    • Numbers (like 10 or 3.14)
    • Words or Text (called strings, like "hello" or "theagleye")
    • True/False values (called booleans)

Important Tips:

 

  • Variable names should be meaningful. Instead of naming it x, try using something that makes sense, like age or total_price.
  • You can’t use special characters (like @, #, or !) in variable names.

 

20+ interview questions that comprehensively cover the concept of variables in Python

Question 1. What is a variable in Python?

Answer: A variable in Python is a name used to store a value, which can be updated or reused later. It acts as a reference to the value.

Example:

x = 10
print(x)

Output:

10

 

Question 2. How do you declare a variable in Python?

Answer: Variables are created by assigning a value using the = operator. Python does not require an explicit declaration.

Example:

name = "Alice"
age = 25

 

Question 3. Can a variable name start with a number?

Answer: No, variable names must start with a letter or an underscore (_).

Example:

1name = "Alice"

Output:

SyntaxError: invalid decimal literal

 

Question 4. What are the rules for naming variables in Python?

Answer:

  • Names must start with a letter or an underscore.
  • Cannot start with a number.
  • Can only contain letters, numbers, and underscores.
  • Cannot be a reserved keyword.

Example:

_valid_name = 5
name1 = "John"

 

Question 5. What are global variables in Python?

Answer: Global variables are defined outside of any function or block and can be accessed throughout the script.

Example:

x = 10  # Global variable

def show():
    print(x)

show()

Output:

10

 

Question 6. What are local variables in Python?

Answer: Local variables are defined inside a function and can only be accessed within that function.

Example:

def show():
    y = 5  # Local variable
    print(y)

show()

Output:

5

 

Question 7. What is the difference between global and local variables?

Answer:

  • Global variables: Accessible throughout the program.
  • Local variables: Accessible only within the function where defined.

 

Question 8. How can you declare a global variable inside a function?

Answer: Use the global keyword to declare a variable as global inside a function.

Example:

def modify():
    global x
    x = 20

modify()
print(x)

Output:

20

 

Question 9. Can Python variables store multiple types of values?

Answer: Yes, Python variables are dynamically typed and can store different types of values at different times.

Example:

x = 10
x = "Hello"
print(x)

Output:

Hello

 

Question 10. What is a constant in Python? How do you define it?

Answer: Python does not have a built-in constant type, but by convention, variables written in UPPERCASE are treated as constants.

 

Question 11. What are the scope and lifetime of a variable?

Answer:

  • Scope: The part of the program where the variable is accessible.
  • Lifetime: The duration for which the variable exists in memory.

 

Question 12. Can you reassign a variable in Python?

Answer: Yes, Python allows reassignment of variables to any value or type.

Example:

x = 10
x = "Python"
print(x)

Output:

Python

 

Question 13. What is variable unpacking in Python?

Answer: Variable unpacking allows you to assign values from an iterable to multiple variables.

Example:

a, b, c = [1, 2, 3]
print(a, b, c)

Output:

1 2 3

 

Question 14. How does Python handle variables internally?

Answer: Python uses references and names to handle variables. A variable name points to an object in memory.

 

Question 15. What are shadowing variables?

Answer: Shadowing occurs when a local variable in a function has the same name as a global variable.

 

Question 16. Can variables hold functions or objects in Python?

Answer: Yes, Python variables can store functions, objects, or any data type.

 

Question 17. What are Python keywords, and can they be used as variable names?

Answer: Keywords are reserved words in Python and cannot be used as variable names.

Example:

and = 5

Output:

and = 5 
    ^^^
SyntaxError: invalid syntax

 

Question 18. What is type hinting in Python variables?

Answer: Type hinting is a way to specify the expected data type of a variable, although Python does not enforce it.

Example:

age: int = 25

 

Question 19. What are f-strings, and how are variables used in them?

Answer: F-strings are formatted string literals that make it easy to embed variables into strings.

Example:

name = "Alice"
print(f"Hello, {name}")

Output:

Hello, Alice

 

Question 20. Can Python variables have Unicode characters in their names?

Answer: Yes, Python allows Unicode characters in variable names.

Example:

नाम = "Python"
print(नाम)

Output:

Python

 

Question 21. What are the default variable types in Python?

Answer: Common types include integers (int), floating-point numbers (float), strings (str), and booleans (bool). Python determines the type dynamically.

 

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