array
— Efficient arrays of numeric values¶
array
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'
wchar_t
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
'Q'
unsigned long long
int
8
'f'
float
float
4
'd'
double
float
8
Notes:
-
It can be 16 bits or 32 bits depending on the platform.
Changed in version 3.9:
array('u')
now useswchar_t
as C type instead of deprecated
Py_UNICODE
. This change doesn’t affect its behavior because
Py_UNICODE
is alias ofwchar_t
since Python 3.3.Deprecated since version 3.3, will be removed in version 4.0.
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()
, orfromunicode()
method (see below)
to add initial items to the array. Otherwise, the iterable initializer is
passed to theextend()
method.Raises an auditing event
array.__new__
with argumentstypecode
,initializer
.
-
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 asarray.buffer_info()[1] *
. This is occasionally useful when working with low-level (and
array.itemsize
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 thefromfile()
method).New in version 3.2:
fromstring()
is renamed tofrombytes()
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.
-
array.
fromlist
(
list
)
¶
-
Append items from the list. This is equivalent to
for x in list:
except that if there is a type error, the array is unchanged.
a.append(x)
-
array.
fromunicode
(
s
)
¶
-
Extends this array with data from the given unicode string. The array must
be a type'u'
array; otherwise aValueError
is raised. Use
array.frombytes(unicodestring.encode(enc))
to append Unicode data to an
array of some other type.
-
array.
index
(
x
[
, start
[
, stop
]
]
)
¶
-
Return the smallest i such that i is the index of the first occurrence of
x in the array. The optional arguments start and stop can be
specified to search for x within a subsection of the array. Raise
ValueError
if x is not found.Changed in version 3.10: Added optional start and stop parameters.
-
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
thetofile()
method.)New in version 3.2:
tostring()
is renamed totobytes()
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.
tounicode
(
)
¶
-
Convert the array to a unicode string. The array must be a type
'u'
array;
otherwise aValueError
is raised. Usearray.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
])
See also
- Module
struct
-
Packing and unpacking of heterogeneous binary data.
- Module
xdrlib
-
Packing and unpacking of External Data Representation (XDR) data as used in some
remote procedure call systems. - NumPy
-
The NumPy package defines another array type.