撤消文件readline()操作，以便文件指针恢复到原始状态 [英] Undo a file readline() operation so file-pointer is back in original state

问题描述

我正在使用file.readline()以只读模式浏览文本文件的Python文件指针，以查找特殊行.找到该行后，我想将文件指针传递给一个方法，该方法期望文件指针位于该读取行的开始位置(而不是紧随其后.)

I'm browsing through a Python file pointer of a text file in read-only mode using file.readline() looking for a special line. Once I find that line I want to pass the file pointer to a method that is expecting the file pointer to be at the START of that readline (not right after it.)

基本上我该如何撤消对文件指针的一个file.readline()操作?

How do I essentially undo one file.readline() operation on a file pointer?

推荐答案

您必须记住位置，方法是在阅读行之前调用file.tell()，然后调用file.seek()进行倒带.像这样:

You have to remember the position by calling file.tell() before the readline and then calling file.seek() to rewind. Something like:

fp = open('myfile')
last_pos = fp.tell()
line = fp.readline()
while line != '':
  if line == 'SPECIAL':
    fp.seek(last_pos)
    other_function(fp)
    break
  last_pos = fp.tell()
  line = fp.readline()

我不记得在for line in file循环内调用file.seek()是否安全，因此我通常只写出while循环.可能有更多的Python方式可以做到这一点.

I can't recall if it is safe to call file.seek() inside of a for line in file loop so I usually just write out the while loop. There is probably a much more pythonic way of doing this.

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