What Is a Variable?
A variable is a name that is used to store a value in your program memory.In simple words, you can think a variable like a box with a label. The box contains the value and its label is name of a variable.
x = 10
name = "Hitesh"
is_ready = TrueYou don’t need to declare the data type of a variable. You don’t need to declare it in Python.
You can change the value (of a variable) any time as shown below:
x = 20
name = "Ramesh"
is_ready = FalseCreating and Assigning Variables
In Python, you can create a variable using the = sign.a = 10
b = 3.14
text = "Hello"Multiple assignments:
You can assign several variables at once in a single line. This helps to make code short and clean.
x, y, z = 10, 20, 30
name = age = city = "New Delhi"In next line, three variables (name, age, and city) get the same value "New Delhi”. This is also known as chained assignment
Augmented assignment:
In this, you update the value of a variable using its own value in a shorter way.
In this type assignment, we use a shortcut operator like +=, -=, *=, or /=.
Example:
• x += 5 means add 5 to x
• x -= 2 means subtract 2 from x
• x *= 3 means multiply x by 3
• x /= 2 means divide x by 2
Example code:
count = 10 # Step 1: Assign initial value 10 to 'count'
count += 20count += 20 means, take the current value of count (10), add 20 to it, and store the new value (30) back into count variable.
Variable Naming Rules & Conventions
In Python, when you create a variable then one needs to follow some rules to avoid error at run time.Rule No 01:
You can not start a variable name with a number as shown below:
Example 01:
2countFollowing error message is shown:
Example 02:
count2 Rule No 02:
A variable name can only have:
• Lowercase letters: a–z
• Uppercase letters: A–Z
• Digits: 0–9
• Underscore: _
Example:
user_name = "Hitesh"
age2 = 25
total_sum = 100Rule No 03:
Python treats uppercase and lowercase as different.
Example: Count and count are two different variables in Python language.
Rule No 04:
In Python, there are some reserved words like class, if, for, while, etc.
These reserved words are called keywords and you cannot use them as variable names.
Variable Types and Mutability
In Python variables, you can store any type of data like:num = 40 # int
price = 19.99 # float
name = "Hitesh" # string
is_open = False # bool
data = [1, 2, 3, 4] # list
info = {"age": 25} # dictMutable vs Immutable
Mutability simply means whether a value can be changed after creation or not.
1. Immutable Example
x = 10
y = x
y = 15
print(x) # 10 -> unchanged10
Here, you can see that changing y value does not affect x because numbers are immutable.
2. Mutable Example
a = [10, 20]
b = a
b.append(30)
print(a) # [10, 20, 30]
print(b) # [10, 20, 30]Output:
[10, 20, 30]
[10, 20, 30]
If we print both lists a and b, the result is [10, 20, 30] because lists are mutable.
Both a and b are of list type and share the same memory location, so when one changes, the other also changes.