array — Efficient arrays of numeric values

This module defines an object type which can compactly represent an array of basic values: characters, integers, floating-point numbers, complex numbers. Arrays are mutable sequence types and behave very much like lists, except that the type of objects stored in them is constrained. The type is specified at object creation time by using a type code, which is a single character. The following type codes are defined:

Type code

C Type

Python Type

Minimum size in bytes

Notes

'b'

signed char

int

1

'B'

unsigned char

int

1

'u'

wchar_t

Unicode character

2

(1)

'w'

Py_UCS4

Unicode character

4

(2)

'h'

signed short

int

2

'H'

unsigned short

int

2

'i'

signed int

int

2

'I'

unsigned int

int

2

'l'

signed long

int

4

'L'

unsigned long

int

4

'q'

signed long long

int

8

'Q'

unsigned long long

int

8

'e'

_Float16

float

2

(3)

'f'

float

float

4

'd'

double

float

8

'Zf'

float complex

complex

8

(4)

'Zd'

double complex

complex

16

(4)

Notes:

  1. It can be 16 bits or 32 bits depending on the platform.

    Changed in version 3.9: array('u') now uses wchar_t as C type instead of deprecated Py_UNICODE. This change doesn’t affect its behavior because Py_UNICODE is alias of wchar_t since Python 3.3.

    Deprecated since version 3.3, will be removed in version 3.16: Please migrate to 'w' typecode.

  2. Added in version 3.13.

  3. The IEEE 754 binary16 “half precision” type was introduced in the 2008 revision of the IEEE 754 standard. This type is not widely supported by C compilers. It’s available as _Float16 type, if the compiler supports the Annex H of the C23 standard.

    Added in version 3.15.

  4. Complex types (Zf and Zd) are available unconditionally, regardless on support for complex types (the Annex G of the C11 standard) by the C compiler. As specified in the C11 standard, each complex type is represented by a two-element C array containing, respectively, the real and imaginary parts.

    Added in version 3.15.

See also

The ctypes and struct modules, as well as third-party modules like numpy, use similar – but slightly different – type codes.

The actual representation of values is determined by the machine architecture (strictly speaking, by the C implementation). The actual size can be accessed through the array.itemsize attribute.

The module defines the following item:

array.typecodes

A tuple with all available type codes.

Changed in version 3.15: The type changed from str to tuple.

The module defines the following type:

class array.array(typecode[, initializer])

A new array whose items are restricted by typecode, and initialized from the optional initializer value, which must be a bytes or bytearray object, a Unicode string, or iterable over elements of the appropriate type.

If given a bytes or bytearray object, the initializer is passed to the new array’s frombytes() method; if given a Unicode string, the initializer is passed to the fromunicode() method; otherwise, the initializer’s iterator is passed to the extend() method to add initial items to the array.

Array objects support the ordinary mutable sequence operations of indexing, slicing, concatenation, and multiplication. When using slice assignment, the assigned value must be an array object with the same type code; in all other cases, TypeError is raised. Array objects also implement the buffer interface, and may be used wherever bytes-like objects are supported.

Raises an auditing event array.__new__ with arguments typecode, initializer.

typecode

The typecode character used to create the array.

itemsize

The length in bytes of one array item in the internal representation.

append(value, /)

Append a new item with the specified value to the end of the array.

buffer_info()

Return a tuple (address, length) giving the current memory address and the length in elements of the buffer used to hold array’s contents. The size of the memory buffer in bytes can be computed as array.buffer_info()[1] * array.itemsize. This is occasionally useful when working with low-level (and inherently unsafe) I/O interfaces that require memory addresses, such as certain ioctl() operations. The returned numbers are valid as long as the array exists and no length-changing operations are applied to it.

Note

When using array objects from code written in C or C++ (the only way to effectively make use of this information), it makes more sense to use the buffer interface supported by array objects. This method is maintained for backward compatibility and should be avoided in new code. The buffer interface is documented in Buffer Protocol.

byteswap()

“Byteswap” all items of the array. This is only supported for values which are 1, 2, 4, 8 or 16 bytes in size; for other types of values, RuntimeError is raised. It is useful when reading data from a file written on a machine with a different byte order. Note, that for complex types the order of components (the real part, followed by imaginary part) is preserved.

count(value, /)

Return the number of occurrences of value in the array.

extend(iterable, /)

Append items from iterable to the end of the array. If iterable is another array, it must have exactly the same type code; if not, TypeError will be raised. If iterable is not an array, it must be iterable and its elements must be the right type to be appended to the array.

frombytes(buffer, /)

Appends items from the bytes-like object, interpreting its content as an array of machine values (as if it had been read from a file using the fromfile() method).

Added in version 3.2: fromstring() is renamed to frombytes() for clarity.

fromfile(f, n, /)

Read n items (as machine values) from the file object f and append them to the end of the array. If less than n items are available, EOFError is raised, but the items that were available are still inserted into the array.

fromlist(list, /)

Append items from the list. This is equivalent to for x in list: a.append(x) except that if there is a type error, the array is unchanged.