Data Types

Basic data types

Type	Description	Example
int	Integer	42
float	Floating point	3.14
str	String	"hello"
bool	Boolean	True / False
NoneType	Null value	None

x = 10          # int
y = 3.14        # float
s = "hello"     # str
b = True        # bool
n = None        # NoneType

Type checking

isinstance()

isinstance(42, int)             # True
isinstance(3.14, float)         # True
isinstance(42, (int, float))    # True (checks multiple types)
isinstance("hi", str)           # True

Tip

isinstance() is the recommended way to check types because it supports inheritance.

type()

type(42)            # <class 'int'>
type(42).__name__   # "int" (returns the type name as a string)
 
# Custom type check
def is_type(value, type_str):
    return type(value).__name__ == type_str
 
is_type(5, "int")   # True

Warning

type() does not account for inheritance. Use isinstance() when possible.

Type conversion

int("42")       # str → int: 42
float("3.14")   # str → float: 3.14
str(42)         # int → str: "42"
bool(1)         # int → bool: True
bool(0)         # int → bool: False
bool("")        # str → bool: False
bool("hello")   # str → bool: True
list("abc")     # str → list: ['a', 'b', 'c']
tuple([1,2])    # list → tuple: (1, 2)

Note

bool() returns False for empty values: 0, 0.0, "", [], {}, (), None.

Numeric validation

Checking if a string is a number

def is_integer(s):
    return s.isdigit()   # True if all characters are digits
 
def is_float(s):
    parts = s.split(".")
    return len(parts) == 2 and parts[0].isdigit() and parts[1].isdigit()
 
is_integer("123")    # True
is_integer("12.3")   # False
is_float("3.14")     # True
is_float("3.1.4")    # False

Tip

For negative numbers, strip the leading - before checking: s.lstrip("-").isdigit().

Integer details

x = 42          # decimal
y = 0b1010      # binary (10)
z = 0o12        # octal (10)
w = 0xA         # hexadecimal (10)
 
large = 1_000_000   # underscores as thousand separators (readability)

Note

Python integers have arbitrary precision: they can be as large as memory allows, with no overflow.

Float details

x = 3.14
y = 2.5e10       # scientific notation: 2.5 × 10^10
z = 1.2e-4       # 0.00012

Warning

Floating point arithmetic can have precision issues:

0.1 + 0.2   # 0.30000000000000004 (not exactly 0.3)

Use round() or the decimal module for precise calculations.

Next: Strings