If the argument defines __int__(), int(x) returns x.__int__(). If the argument defines __index__(), it returns x.__index__(). For floating-point numbers, this truncates towards zero.
If the argument is not a number or if base is given, then it must be a string, bytes, or bytearray instance representing an integer in radix base. Optionally, the string can be preceded by + or - (with no space in between), have leading zeros, be surrounded by whitespace, and have single underscores interspersed between digits.
A base-n integer string contains digits, each representing a value from 0 to n-1. The values 0–9 can be represented by any Unicode decimal digit. The values 10–35 can be represented by a to z (or A to Z). The default base is 10. The allowed bases are 0 and 2–36. Base-2, -8, and -16 strings can be optionally prefixed with 0b/0B, 0o/0O, or 0x/0X, as with integer literals in code. For base 0, the string is interpreted in a similar way to an integer literal in code, in that the actual base is 2, 8, 10, or 16 as determined by the prefix. Base 0 also disallows leading zeros: int('010', 0) is not legal, while int('010') and int('010', 8) are.
The integer type is described in Numeric Types — int, float, complex.
Changed in version 3.4: If base is not an instance of int and the base object has a base.__index__ method, that method is called to obtain an integer for the base. Previous versions used base.__int__ instead of base.__index__.
Changed in version 3.6: Grouping digits with underscores as in code literals is allowed.
Changed in version 3.7: The first parameter is now positional-only.
Changed in version 3.8: Falls back to __index__() if __int__() is not defined.
Changed in version 3.11: int string inputs and string representations can be limited to help avoid denial of service attacks. A ValueError is raised when the limit is exceeded while converting a string to an int or when converting an int into a string would exceed the limit. See the integer string conversion length limitation documentation.
Changed in version 3.14: int() no longer delegates to the __trunc__() method.