Read specific bytes of file in python

Question

I want to specify an offset and then read the bytes of a file like

offset = 5
read(5) 

and then read the next 6-10 etc. I read about seek but I cannot understand how it works and the examples arent descriptive enough.

seek(offset,1) returns what?

Thanks

Answer 1

The values for the second parameter of seek are 0, 1, or 2:

0 - offset is relative to start of file
1 - offset is relative to current position
2 - offset is relative to end of file

Remember you can check out the help -

>>> help(file.seek)
Help on method_descriptor:

seek(...)
    seek(offset[, whence]) -> None.  Move to new file position.

    Argument offset is a byte count.  Optional argument whence defaults to
    0 (offset from start of file, offset should be >= 0); other values are 1
    (move relative to current position, positive or negative), and 2 (move
    relative to end of file, usually negative, although many platforms allow
    seeking beyond the end of a file).  If the file is opened in text mode,
    only offsets returned by tell() are legal.  Use of other offsets causes
    undefined behavior.
    Note that not all file objects are seekable.

Answer 2

Just play with Python's REPL to see for yourself:

[...]:/tmp$ cat hello.txt 
hello world
[...]:/tmp$ python
Python 2.7.6 (default, Mar 22 2014, 22:59:56) 
[GCC 4.8.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> f = open('hello.txt', 'rb')
>>> f.seek(6, 1)    # move the file pointer forward 6 bytes (i.e. to the 'w')
>>> f.read()        # read the rest of the file from the current file pointer
'world\n'