python - Math domain error in fermat -

from math import sqrt  def fermatbook (n):     x=int(sqrt(n))     c=x**2-n     while (sqrt(c)!=int(sqrt(c))):         x=x+1     y=sqrt(c)     a=x+y     b=x-y     if a==1 or b==1:         print "the number prime"     return a, b 

error:

traceback (most recent call last):   file "<pyshell#0>", line 1, in <module>     fermatbook (23867)   file "c:/python27/fermatlivro.py", line 6, in fermatbook     while (sqrt(c)!=int(sqrt(c))): valueerror: math domain error 

i don't know going wrong program... me ?

most variable c going negative:

example

if call:

n = 2  fermatbook(n) 

it assign following values following variables:

x = int(sqrt(n)) = int(1.47...) = 1 c = x**2 - n = 1**2 - 2 = 1 - 2 = -1 

this happen alot on values of n square root not integer.

sqrt(n) >= int(sqrt(n)), n >= 0 

then when call sqrt(c) out of domain because cannot handle negative values.

>>> math import sqrt >>> sqrt(-1) traceback (most recent call last):   file "<stdin>", line 1, in <module> valueerror: math domain error 

you should rather use can handle imaginary numbers, i.e. cmath

or perform checks assure not happen:

as example...

if c < 0:     c = 0  

as fix going run problem:

this infinite loop:

while (sqrt(c)!=int(sqrt(c))):     x=x+1 

you need update c otherwise condidtion never change no matter how many times increment x. meant this?

while (sqrt(c)!=int(sqrt(c))):     x=x+1     c = x**2+n # <--- update c