CODEWITHSUNDEEP
python
this.guy
this.guy

Reputation: 91

Modify only a specific part of a file

I have a python script that is supposed to read a file. The issue is that that file is very large so for efficiency I decided that my script should only read from line 650000 and onward, since previous line does not contain relevant information.

Is there any way to only modify lines 650000 till eof, so for example, if i read() this file only those specific lines would appear?

Upvotes: 2

Views: 274

Answers (1)

unwind
unwind

Reputation: 399803

Files are not line-oriented, they are blocks of bytes.

There's no way, short of reading the data in, to figure out how many bytes make up those first 650,000 lines, so you'd have to do that just in order to skip them.

Starting modifying a file at a certain offset is possible, but that offset will be in bytes which is the addressing unit used by files.

Skipping lines can be done easily enough:

with open("myfile.txt", "w+t") as f:
  for i in xrange(650000):
    f.readline() # Read a line and throw it away
  f.write("hello")

This will truncate the file so that there will be no data after the hello (but 650,000 lines before it, of course).

Upvotes: 2

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