Numeric Conversion Functions

Numeric Conversion Functions
	Chapter 4. Simple Numeric Expressions and Output

We can convert a number from one type to another. A conversion may involve a loss of precision because we've reduced the number of bits available. A conversion may also add a false sense of precision by adding bits which don't have any real meaning.

We'll call these factory functions because they are a factory for creating new objects from other objects. The idea of factory function is a very general one, and these are just the first of many examples of this pattern.

Also, this section is only an introduction. A more complete list of conversion functions is provided in the section called “String Conversion Functions”.

Conversion Function Definitions

There are a number of conversions from one numeric type to another.

int (x) → integer: Generates an integer from the object x. If x is a floating point number, digits to the right of the decimal point are truncated as part of creating an integer. If the floating point number is more than about 10 digits, a long integer object is created to retain the precision. If x is a long integer that is too large to be represented as an integer, there's no conversion. If x is a string, the string is parsed to create an integer value. Complex values can't be turned into integers directly.
float (x) → float: Generates a float from object x. If x is an integer or long integer, a floating point number is created. Note that long integers can have a large number of digits, but floating point numbers only have approximately 16 digits; there can be some loss of precision. Complex values can't turned into floating point numbers directly.
long (x) → long: Generates a long integer from x. If x is a floating point number, digits to the right of the decimal point are truncated as part of creating a long integer.
complex (real, [imag]) → complex: Generates a complex number from real and imag.

If this “complex (real, [imag] )” syntax synopsis is confusing, you might want to see Syntax For Newbies.

Syntax For Newbies

We'll show optional parameters to functions by surrounding them with []'s. In the case of complex, there will be two different ways to use the function, with one parameter, real, or with two parameters, real, imag. We don't actually enter the []'s, they're just hints as to what the two forms of the function are.

In the case of “complex(real, [imag] )”, we have two choices.

>>> complex( 2.0, 3.0 )
(2+3j)
>>> complex( 4.0 )
(4+0j)

Conversion Function Examples

float (x ) creates a floating point number equal to the string or number x. If a string is given, it must be a valid floating point number: digits, decimal point, and an exponent expression. Examples: float("6.02E24"), float(23). This is handy when doing division to prevent getting the simple integer quotient.

For example:

>>> print float(22)/7, 22/7
3.14285714286 3

int (x ) creates an integer equal to the string or number x. If a string is given, it must be a valid decimal integer string. Examples: int("1243"), int(3.14159).

long (x ) creates a long integer equal to the string or number x. If a string is given, it must be a valid decimal integer. The expression long(2) has the same value as the literal 2L. Examples: long(6.02E23), long(2).

For example:

>>> print long(2)**64
18446744073709551616

This shows the range of values possible with 64-bit integers, available on larger computers.

Complex is not as simple as the others. A complex number has two parts, real and imaginary. Conversion to complex typically involves two parameters.

complex (r, [i] ) creates a complex number with the real part of r; if the second parameter, i, is given, this is the imaginary part of the complex number, otherwise the imaginary part is zero. The string must be a valid complex number. Examples:

>>> print complex(3,2), complex(4), complex("3+4j")
(3+2j) (4+0j) (3+4j)

Note that the second parameter, with the imaginary part of the number, is optional. This leads to a number of different ways to call this function. In the example above, we used three variations: two numeric parameters, one numeric parameter and one string parameter.


Numeric Types and Operators		Built-In Functions