为什么在 python 中调用 file.read 会用垃圾填充我的文件？

Question

运行这个：

import os

if __name__ == '__main__':
    exclude = os.path.join(
        r"C:\Dropbox\eclipse_workspaces\python\sync\.git", "info", "exclude")
    with open(exclude, 'w+') as excl:  # 'w' will truncate
        # print excl.read() # empty
        # excl.readall() # AttributeError: 'file' object has no attribute
        # 'readall' -- this also I do not understand
        excl.write('This will be written as expected if I comment the
         line below')
        print "Garbage\n\n", excl.read()
    # if I do not comment the line however, the file contains all the garbage
    # excl.read() just printed (edit: in addition to the line I wrote)

导致我的文件充满垃圾 - 为什么？还有为什么 readall 没有解决？

Python 2.7.3

最新迭代：

#!/usr/bin/env python2
import os

if __name__ == '__main__':
    exclude = os.path.join(r"C:\Users\MrD","exclude")
    with open(exclude,'w+') as excl:
        excl.write('This will be written if I comment the line below')
        print "Garbage\n\n",excl.read()
    # now the file contains all the garbage
    raw_input('Lol >')

Answer 1

您在在 C 级别实现 I/O 的方式上遇到了一个特殊问题。当您以+ 模式打开文件时（在您的情况下是写入和读取），那么您必须在“切换”模式之前发出刷新或搜索，否则行为未定义。在这种情况下，您向文件中添加了未初始化的内存。

在 Python 问题跟踪器中有一个报告：http://bugs.python.org/issue1394612

如果您想读回您所写的内容，解决方法是重新开始：

with open(exclude,'w+') as excl:
    excl.write('This will be written if I comment the line below')
    excl.seek(0)
    print "No more garbage\n\n", excl.read()

你也可以使用冲洗：

with open(exclude,'w+') as excl:
    excl.write('This will be written if I comment the line below')
    excl.flush()
    print "No more garbage, eof so empty:\n\n", excl.read()