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devel / comp.lang.python / Re: File write, weird behaviour

Re: File write, weird behaviour

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From: die...@handshake.de (Dieter Maurer)
Newsgroups: comp.lang.python
Subject: Re: File write, weird behaviour
Date: Sun, 19 Feb 2023 22:06:19 +0100
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by: Dieter Maurer - Sun, 19 Feb 2023 21:06 UTC

Azizbek Khamdamov wrote at 2023-2-19 19:03 +0500:
> ...
>Example 2 (weird behaviour)
>
>file = open("D:\Programming\Python\working_with_files\cities.txt",
>'r+') ## contains list cities
># the following code DOES NOT add new record TO THE BEGINNING of the
>file IF FOLLOWED BY readline() and readlines()# Expected behaviour:
>new content should be added to the beginning of the file (as in
>Example 1)
>file.write("new city\n")
>
>file.readlines()
>file.close()
>
>I could not find anything in documentation to explain this strange
>behaviour. Why is this happening?

The effect of "r+" (and friends) is specified by the C standard.

The Linux doc (of `fopen`) tells us that ANSI C requires that
a file positioning command (e.g. `seek`) must intervene
between input and output operations. Your example above violates
this condition. Therefore, weird behavior is to be expected.

Subject	Author
Re: File write, weird behaviour	Dieter Maurer