On Mon, Feb 26, 2018 at 11:01:49AM -0800, Roger Lea Scherer wrote: > The first step is to input data and then I want to check to make sure > there are only digits and no other type of characters. I thought regex > would be great for this.
I'm going to quote Jamie Zawinski: Some people, when confronted with a problem, think "I know, I'll use regular expressions." Now they have two problems. Welcome to the club of people who discovered that regexes are just as likely to make things worse as better :-( Here's another, simpler way to check for all digits: value = '12345' # for example value.isdigit() The isdigit() method will return True if value contains nothing but digits (or the empty string), and False otherwise. Sounds like just what you want, right? Nope. It *seems* good right up to the moment you enter a negative number: py> '-123'.isdigit() False Or you want a number including a decimal point. Floating point numbers are *especially* tricky to test for, as you have to include: # mantissa optional + or - sign zero or more digits optional decimal point (but no more than one!) zero or more digits but at least one digit either before or after the decimal point; # optional exponent E or e optional + or - sign one or more digits It is hard to write a regex to match floats. Which brings us to a better tactic for ensuring that values are a valid int or float: try it and see! Instead of using the Look Before You Leap tactic: if string looks like an int: number = int(string) # hope this works, if not, we're in trouble! else: handle the invalid input we can use the "Easier To Ask For Forgiveness Than Permission" tactic, and just *try* converting it, and deal with it if it fails: try: number = int(string) except ValueError: handle the invalid input The same applies for floats, of course. Now, one great benefit of this is that the interpreter already knows what makes a proper int (or float), and *you don't have to care*. Let the interpreter deal with it, and only if it fails do you have to deal with the invalid string. By the way: absolute *none* of the turtle graphics code is the least bit relevant to your question, and we don't need to see it all. That's a bit like going to the supermarket to return a can of beans that you bought because they had gone off: "Hi, I bought this can of beans yesterday, but when I got it home and opened it, they were all mouldy and green inside. Here's my receipt, and the can, and here's the can opener I used to open them, and the bowl I was going to put the beans into, and the microwave oven I would have used to heat them up, and the spoon for stirring them, and the toast I had made to put the beans on, and the salt and pepper shakers I use." :-) -- Steve _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor