Why python doesn't exit the script?

Question

I have the following simple python program to find roots of equation with the bisection method:

from numpy import exp
#
def fun(x):
  return 5.0+4.0*x-exp(x)
#
a=3
b=10.0
eps=1.0e-15
#
fa=fun(a)
fb=fun(b)
#
if fa*fb>0:
  print("wrong interval!!!",fa,fb)
  exit()
#
iter=1
while (b-a)>eps:
  c=(a+b)/2.0
  fc=fun(c)
  if fc==0:
    print("x = ",c)
    exit()
  if fc*fa>0:
    a=c
    fa=fc
  else:
    b=c
    fb=fc
  iter+=1
#
print("x = ",c)
print("accuracy = ",'{:.2e}'.format(b-a))
print("f(",c,") =",fun(c))
print(iter," iterations needed")

If I put a in the wrong interval (like a=3) it says that it's the wrong interval, but it continues anyway giving (obviously) a wrong result and four lines of

ERROR:root:Invalid alias: The name less can't be aliased because it is another magic command.

Morover, the kernel dies (I'm using jupyter). Can you help me?

Answer 1

You should use sys.exit("optional custom message") instead of just exit()

This raises a SystemExit exception, while just exit() only makes sense in the context of the interpreter.

import sys
# logic here
if "something bad":
    sys.exit("optional custom message")

The difference is described in detail here! https://stackoverflow.com/a/19747562/4541045