Variables and Data Types in Python — int, float, str, bool and More

A variable stores a value so you can use it later. In Python, think of a variable as a name tag stuck on a value.

1. Creating variables

Just write name = value. No need to declare a type — Python works it out.

name = "Asha"
age = 21
cgpa = 8.7
is_placed = False

print(name, age, cgpa, is_placed)

Asha 21 8.7 False

You can change a variable any time — even to a different type:

x = 10
x = x + 5
print(x)
x = "now I am text"
print(x)

15
now I am text

Naming rules

• Letters, digits and _ only; cannot start with a digit (2marks ✗, marks2 ✓).
• Case-sensitive: Age and age are different.
• Can't use keywords like if, for, class.
• Style: use snake_case for variables: total_marks, student_name.

2. The main data types

Check a type with type()

print(type(42))
print(type(3.5))
print(type("hi"))
print(type(True))

<class 'int'>
<class 'float'>
<class 'str'>
<class 'bool'>

3. Type conversion

Use int(), float(), str() and bool() to convert.

marks = "85"            # text from input or a file
print(int(marks) + 5)   # convert to a number first
print(str(100) + "%")   # convert number to text to join
print(int(9.99))        # int() cuts off the decimal part
print(float(7))

90
100%
9
7.0

"85" + 5 gives a TypeError — you can't add text and a number. Convert first.

Truthy and falsy

bool() of 0, 0.0, "" (empty text), [], {} and None is False. Almost everything else is True.

print(bool(0), bool(""), bool([]), bool("0"), bool(5))

False False False True True

("0" is a non-empty string, so it's True!)

4. Multiple assignment and swapping

a, b, c = 1, 2, 3
a, b = b, a      # swap in one line
print(a, b, c)

2 1 3

Common mistakes

• Adding text and numbers without converting ("Age: " + 21 ✗ → "Age: " + str(21) ✓, or use a comma in print).
• Starting variable names with digits.
• Forgetting that int() cuts decimals rather than rounding (int(9.99) is 9). Use round() to round.

Quick recap

• name = value creates a variable; the type comes from the value.
• Main types: int, float, str, bool, list, tuple, set, dict, None.
• type(x) shows the type; int(), float(), str() convert.
• 0, empty things and None are falsy.