我需要知道如何从python中的文件中读取行,以便我先读取最后一行,然后以这种方式继续,直到光标到达文件的开头.有任何想法吗？
ang*_*son 23
解决这个问题的一般方法是,按行,反向读取文本文件,可以通过至少三种方法解决.
一般的问题是,由于每行可以有不同的长度,您无法事先知道每行在文件中的起始位置,也不知道有多少行.这意味着您需要对问题应用一些逻辑.
With this approach, you simply read the entire file into memory, in some data structure that subsequently allows you to process the list of lines in reverse. A stack, a doubly linked list, or even an array can do this.
Pros: Really easy to implement (probably built into Python for all I know)
Cons: Uses a lot of memory, can take a while to read large files
With this approach, you also read through the entire file once, but instead of storing the entire file (all the text) in memory, you only store the binary positions inside the file where each line started. You can store these positions in a similar data structure as the one storing the lines in the first approach.
Whever you want to read line X, you have to re-read the line from the file, starting at the position you stored for the start of that line.
Pros: Almost as easy to implement as the first approach
Cons: can take a while to read large files
With this approach you will read the file block-wise or similar, from the end, and see where the ends are. You basically have a buffer, of say, 4096 bytes, and process the last line of that buffer. When your processing, which has to move one line at a time backward in that buffer, comes to the start of the buffer, you need to read another buffer worth of data, from the area before the first buffer you read, and continue processing.
This approach is generally more complicated, because you need to handle such things as lines being broken over two buffers, and long lines could even cover more than two buffers.
It is, however, the one that would require the least amount of memory, and for really large files, it might also be worth doing this to avoid reading through gigabytes of information first.
Pros: Uses little memory, does not require you to read the entire file first
Cons: Much hard to implement and get right for all corner cases
There are numerous links on the net that shows how to do the third approach: