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# 8.6. `array` — 高效的数值数组

此模块定义了一种对象类型，可以紧凑地表示基本类型值的数组：字符、整数、浮点数等。 数组属于序列类型，其行为与列表非常相似，不同之处在于其中存储的对象类型是受限的。 类型在对象创建时使用单个字符的 类型码 来指定。 已定义的类型码如下：

类型码 | C 类型 | Python 类型 | 以字节表示的最小尺寸
--- | --- | --- | ---
`'c'` | char | character | 1
`'b'` | signed char | int | 1
`'B'` | unsigned char | int | 1
`'u'` | Py_UNICODE | Unicode 字符 | 2 (see note)
`'h'` | signed short | int | 2
`'H'` | unsigned short | int | 2
`'i'` | signed int | int | 2
`'I'` | unsigned int | long | 2
`'l'` | signed long | int | 4
`'L'` | unsigned long | long | 4
`'f'` | float | float | 4
`'d'` | double | float | 8

注解

The `'u'` typecode corresponds to Python’s unicode character. On narrow Unicode builds this is 2-bytes, on wide builds this is 4-bytes.

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 values stored for `'L'` and `'I'` items will be represented as Python long integers when retrieved, because Python’s plain integer type cannot represent the full range of C’s unsigned (long) integers.

这个模块定义了以下类型：

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, string, or iterable over elements of the appropriate type.

  在 2.4 版更改: Formerly, only lists or strings were accepted.

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

`array.``ArrayType`

  Obsolete alias for `array`.

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 buffer objects are supported.

以下数据项和方法也受到支持：

`array.``typecode`

  用于创建数组的类型码字符。

`array.``itemsize`

  在内部表示中一个数组项的字节长度。

`array.``append`(x)

  添加一个值为 x 的新项到数组末尾。

`array.``buffer_info`()

  返回一个元组 `(address, length)` 以给出用于存放数组内容的缓冲区元素的当前内存地址和长度。 以字节表示的内存缓冲区大小可通过 `array.buffer_info()[1] * array.itemsize` 来计算。 这在使用需要内存地址的低层级（因此不够安全） I/O 接口时会很有用，例如某些 `ioctl()` 操作。 只要数组存在并且没有应用改变长度的操作，返回数值就是有效的。

  注解

  当在 C 或 C++ 编写的代码中使用数组对象时（这是有效使用此类信息的唯一方式），使用数组对象所支持的缓冲区接口更为适宜。 此方法仅保留用作向下兼容，应避免在新代码中使用。 缓冲区接口的文档参见 Buffers and Memoryview Objects。

`array.``byteswap`()

  “字节对调”所有数组项。 此方法只支持大小为 1, 2, 4 或 8 字节的值；对于其他值类型将引发 `RuntimeError`。 它适用于从不同字节序机器所生成的文件中读取数据的情况。

`array.``count`(x)

  返回 x 在数组中的出现次数。

`array.``extend`(iterable)

  将来自 iterable 的项添加到数组末尾。 如果 iterable 是另一个数组，它必须具有 完全 相同的类型码；否则将引发 `TypeError`。 如果 iterable 不是一个数组，则它必须为可迭代对象并且其元素必须为可添加到数组的适当类型。

  在 2.4 版更改: Formerly, the argument could only be another array.

`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)

  添加来自 list 的项。 这等价于 `for x in list: a.append(x)`，区别在于如果发生类型错误，数组将不会被改变。

`array.``fromstring`(s)

  添加来自字符串的项，将字符串解读为机器值的数组（相当于使用 `fromfile()` 方法从文件中读取数据）。

`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.fromstring(unicodestring.encode(enc))` to append Unicode data to an array of some other type.

`array.``index`(x)

  返回最小的 i 使得 i 为 x 在数组中首次出现的序号。

`array.``insert`(i, x)

  将值 x 作为新项插入数组的 i 位置之前。 负值将被视为相对于数组末尾的位置。

`array.``pop`([i])

  从数组中移除序号为 i 的项并将其返回。 可选参数值默认为 `-1`，因此默认将移除并返回末尾项。

`array.``read`(f, n)

  1.5.1 版后已移除: Use the `fromfile()` method.

  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.``remove`(x)

  从数组中移除首次出现的 x。

`array.``reverse`()

  反转数组中各项的顺序。

`array.``tofile`(f)

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

`array.``tolist`()

  将数组转换为包含相同项的普通列表。

`array.``tostring`()

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

`array.``tounicode`()

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

`array.``write`(f)

  1.5.1 版后已移除: Use the `tofile()` method.

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

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

参见

模块 `struct`

  打包和解包异构二进制数据。

模块 `xdrlib`

  打包和解包用于某些远程过程调用系统的 External Data Representation (XDR) 数据。

The Numerical Python Documentation

  Numeric Python 扩展 (NumPy) 定义了另一种数组类型；请访问 http://www.numpy.org/ 了解有关 Numerical Python 的更多信息。