The previous two techniques will start the debugger at the beginning of a Python program. But this third technique is best for long-running processes. To start the debugger within a script, use set_trace().

Now, modify your pdb_example.py file as follows:

import pdb
class Student:
            def __init__(self, std):
                        self.count = std
 
            def print_std(self):
                        for i in range(self.count):
                                    pdb.set_trace()
                                    print(i)
                        return
 
if __name__ == '__main__':
            Student(5).print_std()

Now, run the program as follows:

student@ubuntu:~$ python3 pdb_example.py
> /home/student/pdb_example.py(10)print_std()
-> print(i)
(Pdb) continue
0
> /home/student/pdb_example.py(9)print_std()
-> pdb.set_trace()
(Pdb)

set_trace() is a Python function, therefore you can call it at any point in your program.

So, these are the three ways by which you can start a debugger.