Expect like syntax in Python

[Guy Gascoigne - Piggford]

Option 2 looks really interesting.  I already have the reading separated off
from the actual testing, in effect the read is buffered until the client
code explicitly gobbles it.  For what I'm doing this seems to work quite
well.  Separating off the particular tests like you suggest may not be too
hard, and may make for a very readable script.

I'll give it a try.

Guy

"Albert Hofkamp" <hat at se-46.wpa.wtb.tue.nl> wrote in message
news:slrna602gj.ct4.hat at se-46.wpa.wtb.tue.nl...
> On Sun, 3 Feb 2002 00:25:14 -0800, Guy Gascoigne - Piggford
<guy at wyrdrune.com> wrote:
> >I'm trying to find a way to write something like expect in a python
module,
> >and I'm having trouble getting the syntax the way that I want.  In expect
I
> >can write something like this:
> >
> >expect {
> >    -re "ast login" {
> >           pass
> >           }
> >    -re "ogin" {
> >           send  user
> >           }
> >    -re "sword" {
> >           send password
> >           }
> >}
>
> A known problem :-)
>
> I also already noticed that the existing Expect-like thingies are not much
help
> here, they also mangle the order of the patterns and the actions.
> I have been thinking that the following should be possible:
>
> x = ExpectMatcher() # A random name, needs some more thought
> ... # do some initing stuff, start up a sub-process, connect that to x,
etc
> while not x.ismatched():
>     if x.trymatch('ast login'):
>         pass
>     elif x.trymatch('ogin'):
>         send user
>     elif x.trymatch('sword'):
>         send password
>
> There are at least 2 options for implementation (but I haven't had the
> opportunity to implement either of them).
>
> 1) (stupid way)
>    The x object reads data in the x.ismatched() method. If it has
'enough', it
>    returns false. Python then executes the x.trymatch() methods. In the
method,
>    you compare the imput with the argument. If it matches, you set a flag
that
>    x.ismatched() should return true on the next call, followed by
returning
>    true (so the if test succeeds).
>    If all x.trymatch() calls fail, Python executes the 'x.ismatched()'
again,
>    given you a chance to read more data.
>
> 2) (intelligent way)
>    The x.ismatched() returns false in the first call. Python then executes
the
>    if, and as a result, all the x.trymatch() calls. Store the patterns,
and
>    return false to all of them.
>    On the second call to x.ismatch(), you have a list of patterns, so you
can
>    wait until you have seen a pattern match.
>    At that moment, return false again, and now return false to all
x.trymatch()
>    methods, except the one that matches.
>    Python handles the code in the if branch at that point, and returns to
the
>    while.
>    On the 3rd call to x.ismatched() return true.
>
> (the above scheme should be extended to include time-out)
>
> There are probably other/better implementations possible, I haven't really
> considered alternatives except the above 2.
>
> >Am I missing something?  I'm fairly new to python but I don't see a way
to
>
> Probably not. I took me a few months and a few tricky twists to come up
with
> the above.
> Although the solution seems sound to me, I haven't really tried to
implement it.
>
>
> Albert
> --
> Constructing a computer program is like writing a painting