For a long-running process, where the problem occurs much later in the program execution, it would be much more convenient to start the debugger within the program using the pdb set_trace() directive:

import pdb

class Pdb_test(object):
    def __init__(self, parameter):
        self.counter = parameter
    def go(self):
        for j in range(self.counter):
            pdb.set_trace()
            print ("--->",j)
        return

if __name__ == '__main__':
    Pdb_test(10).go()

set_trace() can be called at any point in the program to debug. For example, it can be called based on conditions, exception handlers, or a specific branch of control instructions.

In this case, the output is as follows: 

-> print ("--->",j)
(Pdb) 

The code run stops, exactly after the pdb.set_trace() statement completes.