Numeric values are immutable, and like everything else in Python, they are represented by objects. To assign a new numeric value to a name is not to “update” that value; it is to create a new object representing the new value and to reassign the reference to the name. If you want to delete a reference to a number object, you need to use del to do it.

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Integer types

The Boolean integer type can have the constant value True or False, which are built-in names assigned to a subclass of the int type. It behaves like an integer value zero or one if used in a numeric context, but prints as True or False (by redefining its str and repr formats). All Python objects have a Boolean True or False value.

Python 2 unified standard sized (previously, architecture-dependent 32 or 64-bit) and unsized long integers. Since then, the standard or “plain” integer is unsized and does not overflow, and no special notation is needed. Binary is represented using the prefix 0b, octal with 0o, and hexadecimal with 0x.

Other numeric types

Double-precision floating point real numbers are implemented as C doubles. The actual degree of precision is architecture- and interpreter-dependent (that is, dependent on the C compiler that built the CPython interpreter). Scientific notation is available using the e suffix.

Decimal floating point numbers are available from the Decimal class in the decimal module.

Complex numbers use the format real+imaginaryj (e.g., 12.34+1j). You can access the attributes n.real, n.imag, and n.conjugate().

Integer type functions (available for integers only)

bin(), oct(), and hex() return string representations. ord() and chr() convert ASCII characters to integer values and integer values to ASCII character strings, respectively.

Other numeric type functions (available for all numeric types)

int(), float(), complex(), and bool() perform two functions: (1) they convert from one numeric type to another; (2) they return the numeric value of a string. int() can take a base parameter for string conversions only. complex() can take separate parameters for the real and imaginary portions, for numeric conversions only.

These functions are factory functions: they create a new instance of a class.

abs() returns absolute value. divmod() returns the tuple (quotient, remainder). pow() can take an optional third parameter (a modulus argument, for applications in cryptography). round() takes an optional parameter, a specified number of decimal places. These arithmetic functions are built in; other functions and tools (e.g., pi, e, sqrt()) are available from the math module, which provides most of the functions in the C standard library math. Random number functions are available from the random module.

int() truncates; floor() rounds to the next smaller integer; round() rounds to the nearest integer.

Sources

Chun, Wesley J. Core Python Programming. 2nd ed, Prentice Hall, 2007. Section 4.6, “Standard Type Built-in Functions”; Chapter 5, “Numbers.”

Lutz, Mark. Learning Python. Third ed., O’Reilly, 2008. Chapter 5, “Numbers.”