Really easy assignment... yet I can't do it.

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September 30th, 2012, 12:25 AM

ika1020

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Really easy assignment... yet I can't do it.

I'm new to python, and for my assignment, I have to write a program, that when the wrong number of digits is given (in this case anything but 4-digits), it prints an error message. I have to set the boolean variable set valid to false & then stop.

It also has to give an error message if there are non-digits in my program. again, set valid to false & then stop.

does anyone have any help that could get me started?

September 30th, 2012, 05:24 PM

b49P23TIvg

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Code:

import sys
import string

class HomeWorkError(ValueError):
    pass

sys.stdout.write('Please enter 4 digits.\n')
a = sys.stdin.readline().strip()
valid = set(a).issubset(set(string.digits)) and (4 == len(a))
if not valid:
    raise HomeWorkError('Digits!  Four characters!')

You're right, it's easy. Untested. Most of my untested codes fail.

Note that I've written this in a style that works with python2 or python3.

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October 2nd, 2012, 06:07 PM

norm850

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Quote:

Originally Posted by ika1020

Not sure if you still need help, or if the above reply helped, but I would do it like this:

If given a number, and we want to return false if it is not 4 digits, then divide the number by 1000, and if the value is greater than or equal to 1, then we know it at least 4 digits, and if the value is greater than or equal to 10, we know it is more than 4 digits.

Hope that can help!

October 2nd, 2012, 06:52 PM

b49P23TIvg

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Yes,
int(math.log10(x)) == 3
is also a test.

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