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Python 3.6.5 Documentation > "array" — Efficient arrays of numeric values

"array" — Efficient arrays of numeric values
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This module defines an object type which can compactly represent an
array of basic values: characters, integers, floating point numbers.
Arrays are 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'" | Py_UNICODE | Unicode character | 2 | (1) |
+-------------+----------------------+---------------------+-------------------------+---------+
| "'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 | (2) |
+-------------+----------------------+---------------------+-------------------------+---------+
| "'Q'" | unsigned long long | int | 8 | (2) |
+-------------+----------------------+---------------------+-------------------------+---------+
| "'f'" | float | float | 4 | |
+-------------+----------------------+---------------------+-------------------------+---------+
| "'d'" | double | float | 8 | |
+-------------+----------------------+---------------------+-------------------------+---------+

Notes:

1. The "'u'" type code corresponds to Python’s obsolete unicode
character ("Py_UNICODE" which is "wchar_t"). Depending on the
platform, it can be 16 bits or 32 bits.

"'u'" will be removed together with the rest of the "Py_UNICODE"
API.

Deprecated since version 3.3, will be removed in version 4.0.

2. The "'q'" and "'Q'" type codes are available only if the
platform C compiler used to build Python supports C "long long",
or, on Windows, "__int64".

New in version 3.3.

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 "itemsize" attribute.

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
list, a *bytes-like object*, or iterable over elements of the
appropriate type.

If given a list or string, the initializer is passed to the new
array’s "fromlist()", "frombytes()", or "fromunicode()" method (see
below) to add initial items to the array. Otherwise, the iterable
initializer is passed to the "extend()" method.

array.typecodes

A string with all available type codes.

Array objects support the ordinary 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.

The following data items and methods are also supported:

array.typecode

The typecode character used to create the array.

array.itemsize

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

array.append(x)

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

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.

array.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.

array.count(x)

Return the number of occurrences of *x* in the array.

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.

array.frombytes(s)

Appends items from the string, interpreting the string as an array
of machine values (as if it had been read from a file using the
"fromfile()" method).

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

array.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. *f* must be a real built-in file
object; something else with a "read()" method won’t do.

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.

array.fromstring()

Deprecated alias for "frombytes()".

array.fromunicode(s)

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

array.index(x)

Return the smallest *i* such that *i* is the index of the first
occurrence of *x* in the array.

array.insert(i, x)

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

array.pop([i])

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.

array.remove(x)

Remove the first occurrence of *x* from the array.

array.reverse()

Reverse the order of the items in the array.

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.)

New in version 3.2: "tostring()" is renamed to "tobytes()" for
clarity.

array.tofile(f)

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

array.tolist()

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

array.tostring()

Deprecated alias for "tobytes()".

array.tounicode()

Convert the array to a unicode string. The array must be a type
"'u'" array; otherwise a "ValueError" is raised. Use
"array.tobytes().decode(enc)" to obtain a unicode string from an
array of some other type.

When an array object is printed or converted to a string, it is
represented as "array(typecode, initializer)". The *initializer* is
omitted if the array is empty, otherwise it is a string if the
*typecode* is "'u'", otherwise it is a list of numbers. The string 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". Examples:

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