Python in a Nutshell, 2nd Edition

Numeric Operations

Python supplies the usual numeric operations, as we’ve just seen in Table 4-2. Numbers are immutable objects: when you perform numeric operations on number objects, you always produce a new number object and never modify existing ones. You can access the parts of a complex object z as read-only attributes z.real and z.imag. Trying to rebind these attributes on a complex object raises an exception.

A number’s optional + or - sign, and the + that joins a floating-point literal to an imaginary one to make a complex number, are not part of the literals’ syntax. They are ordinary operators, subject to normal operator precedence rules (see Table 4-2). For example, -2**2 evaluates to -4: exponentiation has higher precedence than unary minus, so the whole expression parses as -(2**2), not as (-2)**2.

Numeric Conversions

You can perform arithmetic operations and comparisons between any two numbers of Python built-in types. If the operands’ types differ, coercion applies: Python converts the operand with the “smaller” type to the “larger” type. The types, in order from smallest to largest, are integers, long integers, floating-point numbers, and complex numbers.

You can request an explicit conversion by passing a noncomplex numeric argument to any of the built-in number types: int, long, float, and complex. int and long drop their argument’s fractional part, if any (e.g., int(9.8) is 9). You can also call complex with two numeric arguments, giving real and imaginary parts. ...