Strings

How to convert a string to an int in Python

Quick answer

Call int(s). It accepts leading/trailing whitespace and raises ValueError on anything that isn't a valid integer.

s = "42"
n = int(s)
print(n + 8)  # 50

int() accepts a str and returns the integer it represents. Whitespace around the digits is stripped; a leading '+' or '-' is honoured; embedded whitespace or letters raise ValueError.

For bases other than 10, pass the base as the second argument: int('ff', 16) → 255, int('101', 2) → 5. This is how you parse hex or binary from a string.

If you have a string that MIGHT be a number, wrap the call in try/except ValueError — Python has no 'is_integer' equivalent to JavaScript's Number.isInteger() for strings.

Variations

Parse hexadecimal

n = int("ff", 16)     # 255
n = int("0xff", 16)   # also 255

Base can be 2 (binary), 8 (octal), 10 (decimal), 16 (hex), or 0 (auto-detect from prefix).

Safe parse with default

def to_int(s, default=0):
    try:
        return int(s)
    except (ValueError, TypeError):
        return default

Handles both non-numeric strings and None.

Float to int (truncates)

int(3.7)   # 3
int(-3.7)  # -3 (toward zero, not floor)

Use math.floor() if you want -3.7 → -4.

Practise this in your browser

Every how-to has a live lesson. Free tier, no card.

Start free →

Unlock every lesson

Pro — $12/mo, unlimited AI, cancel any time.

See Pro plans →

Get one Python lesson + one career idea every Friday

No spam, no "buy our course now". Three bullets, every Friday. Unsubscribe with one click.