exit to interpreter?

[belinda thom]

Hi,

I'm writing a function that polls the user for keyboard input,
looping until it has determined that the user has entered a valid
string of characters, in which case it returns that string so it can
be processed up the call stack. My problem is this. I'd also like it
to handle a special string (e.g. 'quit'), in which case control
should return to the Python command line as opposed to returning the
string up the call stack.

sys.exit seemed like a good choice, but it exits the python interpreter.

I could use an exception for this purpose, but was wondering if
there's a better way?

--b

[kyosohma]

On Mar 23, 12:52 pm, belinda thom <[e-mail]:

Hi,

I'm writing a function that polls the user for keyboard input,
looping until it has determined that the user has entered a valid
string of characters, in which case it returns that string so it can
be processed up the call stack. My problem is this. I'd also like it
to handle a special string (e.g. 'quit'), in which case control
should return to the Python command line as opposed to returning the
string up the call stack.

sys.exit seemed like a good choice, but it exits the python interpreter.

I could use an exception for this purpose, but was wondering if
there's a better way?

--b

If you're using a function, wouldn't using the keyword "return" work?

Mike

[belinda thom]

On Mar 23, 2007, at 11:04 AM, ky******@gmail.com wrote:

On Mar 23, 12:52 pm, belinda thom <[e-mail]:

>Hi,

I'm writing a function that polls the user for keyboard input,
looping until it has determined that the user has entered a valid
string of characters, in which case it returns that string so it can
be processed up the call stack. My problem is this. I'd also like it
to handle a special string (e.g. 'quit'), in which case control
should return to the Python command line as opposed to returning the
string up the call stack.

sys.exit seemed like a good choice, but it exits the python
interpreter.

I could use an exception for this purpose, but was wondering if
there's a better way?

--b

If you're using a function, wouldn't using the keyword "return" work?

Mike

No, because that just returns to the caller, which is not the Python
interpreter.

[Mel Wilson]

belinda thom wrote:

On Mar 23, 2007, at 11:04 AM, ky******@gmail.com wrote:

>On Mar 23, 12:52 pm, belinda thom <[e-mail]:

>>Hi,

I'm writing a function that polls the user for keyboard input,
looping until it has determined that the user has entered a valid
string of characters, in which case it returns that string so it can
be processed up the call stack. My problem is this. I'd also like it
to handle a special string (e.g. 'quit'), in which case control
should return to the Python command line as opposed to returning the
string up the call stack.

sys.exit seemed like a good choice, but it exits the python
interpreter.

I could use an exception for this purpose, but was wondering if
there's a better way?

A custom-defined exception is probably the best way to jump out of a
stack of nested calls.
Mel.

[kyosohma]

On Mar 23, 1:20 pm, belinda thom <[e-mail]:

On Mar 23, 2007, at 11:04 AM, [e-mail] wrote:

On Mar 23, 12:52 pm, belinda thom <[e-mail]:

Hi,

I'm writing a function that polls the user for keyboard input,
looping until it has determined that the user has entered a valid
string of characters, in which case it returns that string so it can
be processed up the call stack. My problem is this. I'd also like it
to handle a special string (e.g. 'quit'), in which case control
should return to the Python command line as opposed to returning the
string up the call stack.

sys.exit seemed like a good choice, but it exits the python
interpreter.

I could use an exception for this purpose, but was wondering if
there's a better way?

--b

If you're using a function, wouldn't using the keyword "return" work?

Mike

No, because that just returns to the caller, which is not the Python
interpreter.

Sorry...I didn't realize you were calling from another function or
functions. Duh. I agree with the other writer. Use a custom exception.

[belinda thom]

Thanks to all. I had suspected this was the best way to go, but as
I'm fairly new to Python, it seemed worth a check.

--b

On Mar 23, 2007, at 12:48 PM, ky******@gmail.com wrote:

On Mar 23, 1:20 pm, belinda thom <[e-mail]:

>On Mar 23, 2007, at 11:04 AM, [e-mail] wrote:

>>On Mar 23, 12:52 pm, belinda thom <[e-mail]:
Hi,

>>>I'm writing a function that polls the user for keyboard input,
looping until it has determined that the user has entered a valid
string of characters, in which case it returns that string so it
can
be processed up the call stack. My problem is this. I'd also
like it
to handle a special string (e.g. 'quit'), in which case control
should return to the Python command line as opposed to returning
the
string up the call stack.

>>>sys.exit seemed like a good choice, but it exits the python
interpreter.

>>>I could use an exception for this purpose, but was wondering if
there's a better way?

>>>--b

>>If you're using a function, wouldn't using the keyword "return"
work?

>>Mike

No, because that just returns to the caller, which is not the Python
interpreter.

Sorry...I didn't realize you were calling from another function or
functions. Duh. I agree with the other writer. Use a custom exception.

--
http://mail.python.org/mailman/listinfo/python-list

[jay graves]

On Mar 23, 12:52 pm, belinda thom <[e-mail]:

be processed up the call stack. My problem is this. I'd also like it
to handle a special string (e.g. 'quit'), in which case control
should return to the Python command line as opposed to returning the
string up the call stack.

Maybe you are looking for the 'code' module.

http://docs.python.org/lib/module-code.html

....
Jay Graves

[belinda thom]

On Mar 24, 2007, at 4:30 AM, Dennis Lee Bieber wrote:

On Fri, 23 Mar 2007 10:52:09 -0700, belinda thom <bt***@cs.hmc.edu>
declaimed the following in comp.lang.python:

>Hi,

I'm writing a function that polls the user for keyboard input,
looping until it has determined that the user has entered a valid
string of characters, in which case it returns that string so it can
be processed up the call stack. My problem is this. I'd also like it
to handle a special string (e.g. 'quit'), in which case control
should return to the Python command line as opposed to returning the
string up the call stack.

To the Python command line? That seems to imply that you started
Python first, then imported the module with the function and
invoked it.

Yup

Surely you don't expect this to be the normal operational mode for
the program?

Its more for pedagogical purposes. I'm using Python in an undergrad
prog class and I'd like students to be able to either enter one of a
set of simple menu choices or quit to the interpreter. It should be
command-based as opposed to GUI based. Hence the request.

About the only way I know of to short circuit the calling stack
requires using an exception -- and an exception handler at the top-
level
(which, for your stated goal, probably has a "pass" for its body,
so the
top-level will "exit" to the interpreter prompt).

This is similar to Mel's advice, which was what I'd expected but
wanted to verify.

Thanks. For those who've been following this thread, this is the
approach I took.

--b