# `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. 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 |
`'f'` | float | float | 4 |
`'d'` | double | float | 8 |

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.

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 string with all available type codes.

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.

  Arrays are generic over the type of their contents.

  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, or 8 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.

  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.

  fromunicode(ustr, /)

    Extends this array with data from the given Unicode string. The array must have type code `'u'` or `'w'`; otherwise a `ValueError` is raised. Use `array.frombytes(unicodestring.encode(enc))` to append Unicode data to an array of some other type.

  index(value[, start[, stop]])

    Return the smallest i such that i is the index of the first occurrence of value in the array. The optional arguments start and stop can be specified to search for value within a subsection of the array. Raise `ValueError` if value is not found.

    Changed in version 3.10: Added optional start and stop parameters.

  insert(index, value, /)

    Insert a new item value in the array before position index. Negative values are treated as being relative to the end of the array.

  pop(index=-1, /)

    Removes the item with the index i from the array and returns it. The optional argument defaults to `-1`, so that by default the last item is removed and returned.

  remove(value, /)

    Remove the first occurrence of value from the array.

  clear()

    Remove all elements from the array.

    Added in version 3.13.

  reverse()

    Reverse the order of the items in the array.

  tobytes()

    Convert the array to an array of machine values and return the bytes representation (the same sequence of bytes that would be written to a file by the `tofile()` method.)

    Added in version 3.2: `tostring()` is renamed to `tobytes()` for clarity.

  tofile(f, /)

    Write all items (as machine values) to the file object f.

  tolist()

    Convert the array to an ordinary list with the same items.

  tounicode()

    Convert the array to a Unicode string. The array must have a type `'u'` or `'w'`; otherwise a `ValueError` is raised. Use `array.tobytes().decode(enc)` to obtain a Unicode string from an array of some other type.

The string representation of array objects has the form `array(typecode, initializer)`. The initializer is omitted if the array is empty, otherwise it is a Unicode string if the typecode is `'u'` or `'w'`, otherwise it is a list of numbers. The string representation is guaranteed to be able to be converted back to an array with the same type and value using `eval()`, so long as the `array` class has been imported using `from array import array`. Variables `inf` and `nan` must also be defined if it contains corresponding floating-point values. Examples:

    array('l')
    array('w', 'hello \u2641')
    array('l', [1, 2, 3, 4, 5])
    array('d', [1.0, 2.0, 3.14, -inf, nan])

See also

Module `struct`

  Packing and unpacking of heterogeneous binary data.

NumPy

  The NumPy package defines another array type.