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Hi, I would like to ask a question, I'm trying to create a while loop, I'm trying to make the program to recognize string characters, but when finally I found a way to do it now it doesn't recognize negative numbers. Here´s the code, hopefully with some feedback I can correct the issue. r = raw_input ("enter a number:") if r.isdigit() and int(r): print r while r != 0: print r if r > 0: r = int(r)-1 elif r < 0: r = int(r)+1 else: print "enter a valid numeric value"

MIT 6.189 A Gentle Introduction to Programming Using Python (OCW)
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hey ,which language is this code ?
AlexZet: Try adding a test line right after the raw_input print r.isdigit() Enter a negative number. What do you get for True/False from the test line? How is the minus sign being seen?
Hi, ayoup the language is python, algotruneman, l did what you tell me and I'm getting False with negatives, I don't understand why.

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xD I'm reading right now and this functions doesn't allow floats or rational numbers, so do you have any other advise to filter string from this program??
I think AlexZet is trying to point out that a minus sign in raw_input is 'seen' as a string. type(r) gives string. So, I'm thinking to convert to float directly after input...
Yes, you are right, that is the way that a minus sign is seen by that function, you can use just the "input" and python will recognize positive and negative numbers but if I enter a string it will go into the "if" statement and them to the elif due the conditions, then it will try to add one to the variable and it crash, this is what I cannot resolve, sorry for the long answer but maybe I explained myself better this time. This is the code so you can see what I talking about: r = input("enter a number:") while r != 0: print r if r > 0: r = r-1 elif r < 0: r = r+1 else: print "enter a valid numeric value"
when using raw_input(), python always returns a string. You can check wether the answer is an integer using try: try: s = int(r) except ValueError: print "this is not an integer"
This works :D thanks!

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