On Wed, 16 Feb 2005, Tony Meyer wrote:
> >> Is there a better way for raw_input to accept both caps and
> >> lower case letters than:
> [...]
> >> if action == 'y' or action == 'Y':
> >
> > if action in 'yY':
> > dostuff()
> [...]
> > Although, that does mean that if a user enters 'nN' they'll
> > get no, but that shouldn't be a huge problem, and it it does,
> > you can just do a if len(action) != 1...
Hello!
There's one other major problem that's not obvious: watch what happens if
the user just presses Enter:
###
>>> if raw_input("y/n?") in "yY":
... print "Yes!"
...
y/n?
Yes!
###
The empty string "" is a substring of everything. *grin* So the length
check against the input is something we definitely need to do if we take
this approach.
Given that, it's probably safer to go with Tony's:
> if action.lower() == 'y':
and if we end up doing a lot of yes/no questions to the user, it'll
probably be a good idea to write a helper function or two to do the grunt
work of parsing the user's input:
###
def isYes(choice):
return choice.lower() == 'y'
def isNo(choice):
return choice.lower() == 'n'
###
just so that we don't have to worry about the problem anymore.
I see that the original code is written using a tail-call recursion style,
such as one supported by Scheme. Here's the code, with isYes()/isNo()
modifications:
###
def aFunction():
action = raw_input("Perform an action?(y,n): ")
if isYes(action):
anotherFunction()
elif isNo(action):
yetAnotherFunction()
else:
aFunction()
###
Unfortunately, Python doesn't support tail call optimization. *sigh* This
means that the recursion here takes stack space in Python.
To get around Python's lack of tail-call optimization, you may want to use
an explicit loop here instead:
###
def aFunction():
while True:
action = raw_input("Perform an action?(y,n): ")
if isYes(action):
anotherFunction()
break
elif isNo(action):
yetAnotherFunction()
break
###
If you have more questions, please feel free to ask!
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