Python Standard Library

The pdb Module

The pdb module is the standard Python debugger. It is based on the bdb debugger framework.

You can run the debugger from the command line (type n [or next] to go to the next line and help to get a list of available commands):

$ pdb.py hello.py
> hello.py(0)?()
(Pdb) n
> hello.py()
(Pdb) n
hello again, and welcome to the show
--Return--
> hello.py(1)?()->None
(Pdb)

Example 11-2 shows how to start the debugger from inside a program.

Example 11-2. Using the pdb Module

File: pdb-example-1.py

import pdb

def test(n):
    j = 0
    for i in range(n):
        j = j + i
    return n

db = pdb.Pdb()
db.runcall(test, 1)

> pdb-example-1.py(3)test()
-> def test(n):
(Pdb) s
> pdb-example-1.py(4)test()
-> j = 0
(Pdb) s
> pdb-example-1.py(5)test()
-> for i in range(n):
...