Types and Conversions

Every value in Python has a type that determines what operations can be performed on it and how it is stored.

Built-in Types

The four types used most often in early programs are:

int

Whole numbers: 0, 42, -17, 1_000_000.

float

Approximate real numbers: 3.14, -0.5, 2.0, 1.5e3.

str

Strings of characters: "Hello", 'Python', "42".

bool

Boolean truth values: True or False.

Use type() to see the type of any value. Try it in the cell below:

Try it live ▶

>>> type(42)
<class 'int'>
>>> type(3.14)
<class 'float'>
>>> type("Hello")
<class 'str'>
>>> type(True)
<class 'bool'>

Go BackOpen In Tab

Type Conversion

Use the type name as a function to convert between types:

Function	Description	Example
int(x)	Convert to integer (truncates floats)	int(3.9) → 3
float(x)	Convert to float	float(7) → 7.0
str(x)	Convert to string	str(42) → "42"
bool(x)	Convert to bool	bool(0) → False

Try it live ▶

>>> int("42")        # str -> int
42
>>> float("3.14")    # str -> float
3.14
>>> int(3.99)        # float -> int (truncates toward zero)
3
>>> str(100)         # int -> str
'100'
>>> round(3.99)      # rounds instead of truncating
4

Go BackOpen In Tab

Note that int() truncates floats toward zero — it does not round. See for yourself:

Try it live ▶

>>> int(3.9)
3
>>> int(-3.9)
-3

Go BackOpen In Tab

Use round() if you need rounding. Edit the values in the cell above, and try converting a string that is not a number (for example int("hello")) to see the ValueError Python raises.

Boolean Values and Truthiness

True and False are the two boolean values. Every Python value can be interpreted as boolean in a condition:

• Falsy values: 0, 0.0, "" (empty string), [] (empty list), {} (empty dict), None

• Truthy values: everything else

Run these conversions to see truthiness in action:

Try it live ▶

>>> bool(0)
False
>>> bool(1)
True
>>> bool("")
False
>>> bool("hello")
True

Go BackOpen In Tab

None

None is a special value that represents the absence of a value. It is Python’s equivalent of null. Try assigning and testing it:

Try it live ▶

>>> x = None
>>> x is None
True
>>> print(x)
None

Go BackOpen In Tab

Functions that do not explicitly return a value return None automatically. None is also used as a placeholder when a variable exists but has not been given a meaningful value yet.

Test for None with is None, not with == None:

if result is None:
    print("No result yet.")