In the context of a file object, the seek function changes the stream position to a given byte offset, with an optional argument of where to offset from. While you can find the official documentation here, it can be unclear how to actually use this feature, so keep reading to see examples on how to use it.
File named example:
foobar
spam eggsf = open('example', 'rb')f.seek(3, 0), our stream position will move 3 bytes forward relative to the beginning of the stream. Now if we then did f.read(1) to read a single byte from where we are in the stream, it would return the string 'b' from the 'b' in 'foobar'. Notice that the 'b' is the 4th character. Also note that after we did f.read(1), we moved the stream position again 1 byte forward relative to the current position in the stream. So the stream position is now currently at position 4.
Now lets do f.seek(4, 1). This will move our stream position 4 bytes forward relative to our current position in the stream. Now if we did f.read(1), it would return the string 'p' from the 'p' in 'spam' on the next line. Note this time that the character at position 6 is the newline character '\n'.
Finally, lets do f.seek(-4, 2), moving our stream position backwards 4 bytes relative to the end of the stream. Now if we did f.read() to read everything after our position in the file, it would return the string 'eggs' and also move our stream position to the end of the file.
Note
- For the second argument in seek(), use os.SEEK_SET, os.SEEK_CUR, and os.SEEK_END in place of 0, 1, and 2 respectively.
- os.SEEK_CUR is only usable when the file is in byte mode.