pdb debugger

#preinstalled package
import pdb; pdb.set_trace()

import pdb
def fact(x):
   f = 1
   for i in range(1,x+1):
      pdb.set_trace()
      print (i)
      f = f * i
   return f
if __name__=="__main__":
   print ("factorial of 3=",fact(3))

import ipdb; ipdb.set_trace()