raw_input() returns a string – not a float.

Try:

1. float(raw_input())
2. eval(raw_input())
3. input() (same as 2)

1. is probably the best choice as it’s clearest and you’ll end up with either a float or an error.

Also, I’m not sure if you want to use y==x as your stopping condition. Probably better to use

if abs(y-x) < e:
break

where e is some small number. Good luck!

Good luck with your Python endeavors.

Traceback (most recent call last):
File “nr.py”, line 4, in
x = random.randint(1,a-1)
File “/usr/lib/python2.5/random.py”, line 215, in randint
return self.randrange(a, b+1)
File “/usr/lib/python2.5/random.py”, line 171, in randrange
raise ValueError, “non-integer stop for randrange()”
ValueError: non-integer stop for randrange()

The last line tells you what the error was, and the indented text above it tells you where it happened. The first section (starting with “File”) tells you where in the topmost file the error happened: your program called random.randint. The second section tells you that random.randint called the randrange function. And the third/last section tells you that randrange has a problem with non-integers and raised an exception.

Look up the documentation for random.randrange and you’ll see that it requires integer bounds, but you’re supplying a floating-point (non-integer) upper bound. To fix this, try replacing:

x = random.randint(1,a-1)

with:

x = random.randint(1, int(a-1))

The code still won’t work with certain input values: try 0, 1, -5, etc. See if you can get your code to work properly (at least, not crash) with such values. Good luck!