What Is A Stream Position Pointer In Python Handling Of Files

1 min readFeb 5, 2022

The aim of this page📝 is to explain the concept of stream position pointer essential for file handling with Python.

1. NOTES

stream position is similar to a pointer
you get it by tell() function
you set it by seek() function
for binary files, it is a byte offset from the start of the file.
in text files, it is just an offset meaningful to the file object — the docs call it an opaque number
it has no defined physical meaning in terms of how the file is stored on disk
but in both modes (binary/test): it is an offset from the start
the start, therefore, has the stream position 0
the stream position is where the next operation will start from — not where the current one finished
after you’ve written a string to the file, the stream position is usually one offset value past the last char
when you’ve just opened a file, the offset is usually 0 or the end of the file, this depends on the mode file handling
it is 0 if you've opened it in r mode (read)
it is the end if you’ve opened it in a (append)
if at the end, it is +1 from the maximum value you could read from without getting EOF error
the two are equivalent for w and w+ modes since those truncate the file to zero bytes