Python 2.7 中的 Open() 和 codecs.open() 表现出奇怪的不同
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Open() and codecs.open() in Python 2.7 behave strangely different
提问by Kriattiffer
I have a text file with first line of unicode characters and all other lines in ASCII. I try to read the first line as one variable, and all other lines as another. However, when I use the following code:
我有一个文本文件，其中包含第一行 unicode 字符和所有其他 ASCII 行。我尝试将第一行作为一个变量读取，将所有其他行作为另一个变量读取。但是，当我使用以下代码时：
# -*- coding: utf-8 -*-
import codecs
import os
filename = '1.txt'
f = codecs.open(filename, 'r3', encoding='utf-8')
print f
names_f = f.readline().split(' ')
data_f = f.readlines()
print len(names_f)
print len(data_f)
f.close()
print 'And now for something completely differerent:'
g = open(filename, 'r')
names_g = g.readline().split(' ')
print g
data_g = g.readlines()
print len(names_g)
print len(data_g)
g.close()
I get the following output:
我得到以下输出：
<open file '1.txt', mode 'rb' at 0x01235230>
28
7
And now for something completely differerent:
<open file '1.txt', mode 'r' at 0x017875A0>
28
77
If I don't use readlines(), whole file reads, not only first 7 lines both at codecs.open() and open().
如果我不使用 readlines()，则会读取整个文件，而不仅仅是 codecs.open() 和 open() 的前 7 行。
Why does such thing happen? And why does codecs.open() read file in binary mode, despite the 'r' parameter is added?
为什么会发生这样的事情？为什么 codecs.open() 以二进制模式读取文件，尽管添加了 'r' 参数？
Upd: This is original file: http://www1.datafilehost.com/d/0792d687
更新：这是原始文件：http: //www1.datafilehost.com/d/0792d687
采纳答案by Martijn Pieters
Because you used .readline()first, the codecs.open()file has filled a linebuffer; the subsequent call to .readlines()returns onlythe buffered lines.
因为你使用了.readline()first，codecs.open()文件已经填满了一个行缓冲区；随后的调用只.readlines()返回缓冲的行。
If you call .readlines()again, the rest of the lines are returned:
如果.readlines()再次调用，则返回其余行：
>>> f = codecs.open(filename, 'r3', encoding='utf-8')
>>> line = f.readline()
>>> len(f.readlines())
7
>>> len(f.readlines())
71
The work-around is to not mix .readline()and .readlines():
解决方法是不要混合.readline()和.readlines()：
f = codecs.open(filename, 'r3', encoding='utf-8')
data_f = f.readlines()
names_f = data_f.pop(0).split(' ') # take the first line.
This behaviour is really a bug; the Python devs are aware of it, see issue 8260.
这种行为确实是一个错误；Python 开发人员知道这一点，请参阅issue 8260。
The other option is to use io.open()instead of codecs.open(); the iolibrary is what Python 3 uses to implement the built-in open()function and is a lot more robust and versatile than the codecsmodule.
另一种选择是使用io.open()而不是codecs.open(); 该io库是 Python 3 用来实现内置open()函数的，并且比codecs模块更加健壮和通用。
