[Tutor] How and where to use pass and continue
python.programming at gmail.com
Mon Mar 28 05:23:59 CEST 2005
Ok I have another question now I noticed that at the tope of a while
loop there will be somthing like this:
test = None
while test != "enter":
test = raw_input("Type a word: ")
if test == "enter":
what is the purpose of test = None ?
On Sun, 27 Mar 2005 22:13:45 -0500, Kevin <python.programming at gmail.com> wrote:
> That was a great help I understand now what they do and how to use
> them. Thanks alot for all your help.
> On Sun, 27 Mar 2005 21:43:45 -0500, Bill Mill <bill.mill at gmail.com> wrote:
> > On Sun, 27 Mar 2005 20:37:02 -0500, Kevin <python.programming at gmail.com> wrote:
> > > I am having lot of trouble learning where and when to use pass and
> > > continue. The two books that I use don't explian these very good. Is
> > > there a website the explains these is great detail?
> > > I have also looked at the python tutorial as well.
> > Kevin,
> > I'll try to help you out - pass and continue are pretty simple
> > concepts. Consider the following code snippet which I will try to use
> > to explain both:
> > command = None
> > while command != '3':
> > command = raw_input("Press 1 to pass, 2 to continue, or 3 to exit ")
> > if command == '1':
> > print "passing"
> > pass
> > elif command == '2':
> > print "continuing"
> > continue
> > else:
> > print "othering"
> > print "end of loop reached"
> > print "exiting"
> > PASS
> > The 'pass' statement simply means 'do nothing'. In the example above,
> > when the python interpreter encounters the pass statement, it simply
> > continues with its execution as it normally would. It is usually used
> > as the only statement in the body of an if statement to denote
> > explicitly that nothing is to be done. I will often use it as a
> > placeholder so that a program compiles correctly, like:
> > if 'a':
> > do_something()
> > elif 'b':
> > #TODO: implement do_something_else()
> > pass
> > elif 'c':
> > quit_foo()
> > Without the pass statement, there are no statements in the second
> > block, and python will raise a SyntaxError.
> > In the first example above, Python sees the pass, exits the series of
> > 'If...elif..." conditions, advances to the final statement of the
> > while loop, prints "end of loop reached", and resumes execution at the
> > top of the loop.
> > CONTINUE
> > The continue statement means what it says - continue with the loop,
> > but resume execution at the top of the loop. In the case of a while
> > loop, the exit condition will be evaluated again, and execution
> > resumes from the top. In the case of a for loop, the item being
> > iterated over will move to its next element. Thus,
> > for i in (1,2):
> > print i
> > continue
> > print "we never get here"
> > Will print 1, hit the continue, update i to the value 2, print 2, hit
> > the continue, and exit because there are no more iterations for i.
> > In the first example I gave, after python reaches the continue,
> > 'command' is again evaluated to see if its value is 3, then the loop
> > proceeds from the top down. If you run the example, you should be able
> > to figure out what's going on.
> > There are a couple more wrinkles - for example, continue only works on
> > the innermost loop in its execution context - but generally, they work
> > as you expect. The longer you work with python, the more you'll find
> > this to be the case, but I'm biased.
> > Hope this helps, and feel free to ask questions about what you don't understand.
> > Peace
> > Bill Mill
> > bill.mill at gmail.com
> > >
> > > Thanks
> > >
> > > Kevin
> > > _______________________________________________
> > > Tutor maillist - Tutor at python.org
> > > http://mail.python.org/mailman/listinfo/tutor
> > >
More information about the Tutor