file.read Method Documentation (Python 2.7.10)

[Stephen Tucker]

Chris,

Thanks for this clarification.

I have not found documentation that disagrees with you. I simply observe
that the documentation that I have alluded to earlier in this chain
(section 5.9 File Objects) could have been made clearer by the addition of
a note along the lines that the behaviour of a file's read method (in
particular, what the unit of information is that it reads (that is, "byte",
"UTF-8 encoded character", or whatever)) depends on the way in which the
file has been opened.

Thank you, Chris (and others) for your attention to my request. I consider
this enquiry closed.

Stephen.




On Wed, Jan 11, 2023 at 5:36 PM Chris Angelico <rosuav at gmail.com> wrote:

> On Thu, 12 Jan 2023 at 04:31, Stephen Tucker <stephen_tucker at sil.org>
> wrote:
> > 1. Create BOM.txt
> > 2. Input three bytes at once from BOM.txt and print them
> > 3. Input three bytes one at a time from BOM.txt and print them
>
> All of these correctly show that a file, in binary mode, reads and writes
> bytes.
>
> > 4. Input three bytes at once from BOM.txt and print them
> > >>> import codecs
> > >>> myfil = codecs.open ("BOM.txt", mode="rb", encoding="UTF-8")
>
> This is now a codecs file, NOT a vanilla file object. See its docs here:
>
> https://docs.python.org/2.7/library/codecs.html#codecs.open
>
> The output is "codec-dependent" but I would assume that UTF-8 will
> yield Unicode text strings.
>
> > 5. Attempt to input three bytes one at a time from BOM.txt and print them
> > -------------------------------------------------------------------------
> >
> > >>> myfil = codecs.open ("BOM.txt", mode="rb", encoding="UTF-8")
> > >>> myBOM_4 = myfil.read (1)
> > >>> myBOM_4
> > u'\ufeff'
>
> > A. The attempt at Part 5 actually inputs all three bytes when we ask it
> to input just the first one!
>
> On the contrary; you asked it for one *character* and it read one
> character.
>
> Where were you seeing documentation that disagreed with this?
>
> ChrisA
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