int() — Convert to Integer

int() converts a possible value into an integer (int).

In this lesson you'll learn which data types can be converted, why some fail, and the difference between int(12.34) and int("12.34").

What you'll learn

• The purpose of int()
• Convert float, bool, and integer-looking strings
• Understand TypeError vs ValueError
• Know why identical digits can produce different results

What does int() do?

int() creates a new integer object from another value, but only if the conversion is valid.

number = int(value)

The original value is never modified.

Example 1 — Float → Integer (Possible)

The decimal part is truncated toward zero. It is not rounded.

a = 12.34
print(a, type(a))

b = int(a)
print(b, type(b))

print(int(0.345))

12.34 <class 'float'>
12 <class 'int'>
0

Key concept: int(12.99) becomes 12, not 13. Python simply removes the fractional part.

Example 2 — Boolean → Integer (Possible)

Python treats booleans as numeric values internally.

Boolean	int() result
True	1
False	0

print(int(True))    # 1
print(int(False))   # 0

Example 3 — Complex → Integer (Not Possible)

Complex numbers contain a real and imaginary part, so int() rejects them.

a = 2 + 3j

# int(a)

TypeError: int() argument must be a string, a bytes-like object or a real number, not 'complex'

This is a TypeError because the type itself is unsupported.

Example 4 — String → Integer

A string works only if its contents represent a valid base-10 integer.

Valid integer strings

print(int("12"))
print(int("123"))
print(int("-45"))

12
123
-45

Invalid string examples

Input	Why it fails
"12.34"	Decimal point → ValueError
"True"	Text, not boolean → ValueError
"2+3j"	Complex literal text → ValueError
"PYTHON"	Not a number → ValueError

Interactive playground

Select a source type and see how int() behaves.

The most important difference

These two values look similar, but one succeeds and the other fails.

	Call	Result	Input type
Works	int(12.34)	12	float
Fails	int("12.34")	ValueError	string

Why?

• 12.34 is already a float, so Python truncates it.
• "12.34" is text, and it is not a valid integer literal.

Complete conversion map

Source	Example	Result
float	int(12.34)	12
bool	int(True)	1
bool	int(False)	0
complex	int(2+3j)	TypeError
str	int("12")	12
str	int("12.34")	ValueError
str	int("True")	ValueError
str	int("2+3j")	ValueError
str	int("PYTHON")	ValueError

Practice exercises

Try predicting the output before running the code.

Exercise 1 — What will these return?

int(0.345)
int(-3.9)

Answer: 0 and -3

Exercise 2 — Which one succeeds?

int("12")
int("12.34")

Answer: Only int("12") works.

Exercise 3 — Compare these:

int(True)
int("True")

Answer: The first returns 1. The second raises ValueError.

Quick knowledge check

1. What does int(12.34) return?
   12 — the fraction is removed, not rounded.

2. Why does int("12.34") fail?
   The string is not a valid base-10 integer literal.

3. Why does int(2+3j) fail?
   It raises TypeError because complex is not a supported real-number type for int().

Summary

• int() converts a possible value into an integer.
• float and bool convert successfully.
• complex raises TypeError.
• Only integer-looking strings convert.
• Golden rule: int(12.34) works. int("12.34") is a ValueError.