Python in a Nutshell

The array Module

The array module supplies a type, also called array, whose instances are mutable sequences, like lists. An array a is a one-dimensional sequence whose items can be only characters, or only numbers of one specific numeric type that is fixed when a is created.

The extension module Numeric, covered later in this chapter, also supplies a type called array that is far more powerful than array.array. For advanced array operations and multidimensional arrays, I recommend Numeric even if your array elements are not numbers.

array.array is a simple type, whose main advantage is that, compared to a list, it can save memory to hold objects all of the same (numeric or character) type. An array object a has a one-character read-only attribute a .typecode, set when a is created, that gives the type of a’s items. Table 15-2 shows the possible type codes for array.

Table 15-2. Type codes for the array module

Type code	C type	Python type	Minimum size
'c'	char	str (length 1)	1 byte
'b'	char	int	1 byte
'B'	unsigned char	int	1 byte
'h'	short	int	2 bytes
'H'	unsigned short	int	2 bytes
'i'	int	int	2 bytes
'I'	unsigned	long	2 bytes
'l'	long	int	4 bytes
'L'	unsigned long	long	4 bytes
'f'	float	float	4 bytes
'd'	double	float	8 bytes

The size in bytes of each item may be larger than the minimum, depending on the machine’s architecture, and is available as the read-only attribute a .itemsize. Module array supplies just one function, a factory ...