On 2023-02-19 16:57:02 +0000, Axy via Python-list wrote: > Looks like the data to be written is buffered, so actual write takes place > after readlines(), when close() flushes buffers. > > See io package documentation, BufferedIOBase. > > The solution is file.flush() after file.write()
Or alternatively, file.seek() to the intended position when switching
between reading and writing. (The C standard says you have to do this. I
can't find it in the Python docs, but apparently Python behaves the
same.)
> On 19/02/2023 14:03, Azizbek Khamdamov wrote:
> > 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")
Also note that you can't ADD anything at the beginning (or in the
middle) of a file. You will overwrite existing content if you try this.
You can only add at the end of the file. If you want to insert
something, you have to rewrite everything from that position.
(So typically, for small files you wouldn't update a file in place, you
would just replace it completely. For large data sets which need to be
updated you would generally use some kind of database.)
hp
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| | | h...@hjp.at | -- Charles Stross, "Creative writing
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