Here are questions students raised about the Data Types worksheet, along with my answers:

QUESTION 1 (Thu, 31 Jan 2008 15:51:36)
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While trying one of the worksheet questions that required a numeric input i tried to make it a bit more generic by adding a few lines that would comment if what was entered wasn't a number. I tried the following but this won't do as it returns false for minus signs and decimal points.

#!/usr/bin/python
string = raw_input('enter text')
if string.isdigit():
	print 'ok'
else:
	print 'not a number'


Then i tried to just find negative numbers with this but i get syntax error on the 'and'.

#!/usr/bin/python
dat = raw_input('number please')
# check if first char is - and rest are digits
if dat[0]==- and dat[1:].isdigit():
        print 'found negative number'
else:
        print 'found something else'


Is there any way, that i can do, to solve this and find if a string is any kind of number?

Answer
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Put the minus sign in quotes (you're checking for a minus sign character), i.e., dat[0]=='-'