[Tutor] EOF problems

[Michael Janssen]

On Wed, 28 Jan 2004, Christopher Spears wrote:

> My instructor claims that Ctrl-Z in Windows is the
> equivalent of an EOF.  However, this is not what I
> have discovered.  Ctrl-Z is the undo command in IDLE.
> Instead, I used Ctrl-C, which is the copy command.
> Since there was an empty string, the script stopped.
> Here is the result:

the gui or the application might catch every controlkey before it gets
passed to python and raw_input. Try to receive alt+F4 with raw_input and
you know what I mean ;-)

When idle catches crtl-Z, there's not much you can do about (unless
configure/rewrite idle). Once I have defined a shortcut strg-alt-Q
unders w98 and I needed a long time to realize why the heck notepad
didn't want and @ sign any longer (uhm, under windows - w98 at least
- strg+alt modifier acts the same like "Alt Gr").

Besides such wonders, your task wouldn't be solved once you found a EOF
key. What is python supposed to do, when an function like raw_input
recieved EOF instead of string-input? raw_input then can't return a
string and must therefore throw an exception to inform the user, there
is no string, not even the empty string.

Look here under linux where EOF is crtl-D:

>>> raw_input("I will type in ctrl+D soon: ")
I will type in ctrl+D soon: Traceback (most recent call last):
  File "<stdin>", line 1, in ?
EOFError

This means, when you want to interrupt a while+raw_input loop with
non-string-input, you must catch the exception:

while 1:
    try:
        s = raw_input("prompt: ")
    except (EOFError, KeyboardInterrupt):
        # user pressed ctrl-D (under linux)
        #  or ctrl-C --> KeyboardInterrupt
        print # end in newline
        break


In case ctrl-C will allways trow TypeError (and isn't dependend of the
content of the clipboard), you found your solution and only have to
silence the Exception.


Michael

> >>>
> Type a string:asdfjk;l
> Type a string:asdfj;
> Type a string:asdfj
>
> Traceback (most recent call last):
>   File "C:\Documents and Settings\Christstopher
> Spears\My Documents\python\unit7question2.py", line 4,
> in -toplevel-
>     s = raw_input ('Type a string:')
> TypeError: object.readline() returned non-string
> >>>
>
> Ok, so the script works, but what is the EOF signal in
> IDLE?  Reading the docs, I seemed to gather that when
> reading a file, Python sees an empty string as the
> EOF.  Am I wrong?  Is there some variable that can be
> used to signal EOF to Python?  I have already tried
> eof.
>
> -Chris
>
>
>
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