什么是Python缓冲区类型?

问题:什么是Python缓冲区类型?

bufferpython中有一个类型,但是我不知道如何使用它。

Python文档中,描述为:

buffer(object[, offset[, size]])

object参数必须是支持缓冲区调用接口的对象(例如字符串,数组和缓冲区)。将创建一个引用该对象参数的新缓冲区对象。缓冲区对象将从对象的开头(或指定的偏移量)开始是一个切片。切片将延伸到对象的末尾(或具有由size参数指定的长度)。

There is a buffer type in python, but I don’t know how can I use it.

In the Python doc the description is:

buffer(object[, offset[, size]])

The object argument must be an object that supports the buffer call interface (such as strings, arrays, and buffers). A new buffer object will be created which references the object argument. The buffer object will be a slice from the beginning of object (or from the specified offset). The slice will extend to the end of object (or will have a length given by the size argument).


回答 0

用法示例:

>>> s = 'Hello world'
>>> t = buffer(s, 6, 5)
>>> t
<read-only buffer for 0x10064a4b0, size 5, offset 6 at 0x100634ab0>
>>> print t
world

在这种情况下,缓冲区是一个子字符串,从位置6开始,长度为5,并且不占用额外的存储空间-它引用字符串的一部分。

这对于像这样的短字符串不是很有用,但是在使用大量数据时可能是必需的。这个例子使用了可变的bytearray

>>> s = bytearray(1000000)   # a million zeroed bytes
>>> t = buffer(s, 1)         # slice cuts off the first byte
>>> s[1] = 5                 # set the second element in s
>>> t[0]                     # which is now also the first element in t!
'\x05'

如果您想对数据有多个视图并且不想(或不能)在内存中保存多个副本,这将非常有用。

请注意,尽管您可以在Python 2.7中使用它,但是buffer已经被memoryviewPython 3中的更好名称所代替。

还要注意,如果不深入研究C API,就不能为自己的对象实现缓冲区接口,即,不能在纯Python中做到这一点。

An example usage:

>>> s = 'Hello world'
>>> t = buffer(s, 6, 5)
>>> t
<read-only buffer for 0x10064a4b0, size 5, offset 6 at 0x100634ab0>
>>> print t
world

The buffer in this case is a sub-string, starting at position 6 with length 5, and it doesn’t take extra storage space – it references a slice of the string.

This isn’t very useful for short strings like this, but it can be necessary when using large amounts of data. This example uses a mutable bytearray:

>>> s = bytearray(1000000)   # a million zeroed bytes
>>> t = buffer(s, 1)         # slice cuts off the first byte
>>> s[1] = 5                 # set the second element in s
>>> t[0]                     # which is now also the first element in t!
'\x05'

This can be very helpful if you want to have more than one view on the data and don’t want to (or can’t) hold multiple copies in memory.

Note that buffer has been replaced by the better named memoryview in Python 3, though you can use either in Python 2.7.

Note also that you can’t implement a buffer interface for your own objects without delving into the C API, i.e. you can’t do it in pure Python.


回答 1

我认为在将python与本机库接口时,缓冲区非常有用。(Guido van Rossum buffer此邮件列表帖子中进行了解释)。

例如,numpy似乎使用缓冲区进行有效的数据存储:

import numpy
a = numpy.ndarray(1000000)

a.data是:

<read-write buffer for 0x1d7b410, size 8000000, offset 0 at 0x1e353b0>

I think buffers are e.g. useful when interfacing python to native libraries. (Guido van Rossum explains buffer in this mailinglist post).

For example, numpy seems to use buffer for efficient data storage:

import numpy
a = numpy.ndarray(1000000)

the a.data is a:

<read-write buffer for 0x1d7b410, size 8000000, offset 0 at 0x1e353b0>