Control of flow

[Tom Good]

Campbell <cb921 at voice.co.za> wrote in message news:<Pine.LNX.4.31.0107311355450.2321-100000 at cb921.local>...
> Hi,
> 
> I use python to write telephony apps, and I find that a 'goto' is often
> a nice tool (stop going 'aargh', its properly "useful" sometimes =).
> 
> Here is a little snippet that gets a month/day from a caller.  If the
> day entered is not in the range of days valid for the month entered, we
> repeat from the top.  Does anyone have a few minutes to waste helping
> me??  How better can I code things that look like this:
> 
> >>> snip <<<
> while 1:
>     cont = 1         ## ugh!
>     month = getdtmf("enter2digs.vox", 2)
>     if month < 1 or month > 12:
>         play("invalidmonth.vox")
>         continue
>     while 1:
>         day = getdtmf("enterday", 2)
>         if day < 1 or day > Month[month]:
>             play("invalidday.vox")
>             cont = 1
>         cont = 0
>     if cont == 1:
>         continue
>     break
> >>> snip <<<

Here's a quick example of the kind of thing you might do instead.  I
have NOT tested this code -- when I write pseudocode, I write it in
Python ;-)

This shows an approach using functions and exceptions instead of loop
control variables.


class startOverException(Exception):
      pass

def someMainFunction():
    # . . .
    month, day = getMonthAndDay()
    # . . .
 
def getMonthAndDay():
    while 1:
        try: 
            month = getmonth()
            day = getday(month)
            return (month, day)
        except startOverException:
            pass # try again from the top

def getmonth():
    while 1:
        month = getdtmf("enter2digs.vox")
        if month < 1 or month >12:
           play("invalidmonth.vox")
        else:
           return month

def getday(month):
    while 1:
        day = getdtmf("enterday", 2)
        if day < 1:
            play("invalidday.vox") # re-enter day
        elif day > Month[month]:
            play("invalidday.vox")
            raise startOverException  # start over, re-enter month
        else:
            return day   # day was OK