The bdb module

The “bdb” module provides the bdb.Bdb class, which you can subclass to create your own debugger. You can then override its methods to define custom behavior for breakpoints, tracing, and handling exceptions.

Here’s a simple example of using the “bdb” module to create a basic debugger:

pythonCopy codeimport bdb

class MyDebugger(bdb.Bdb):
    def user_line(self, frame):
        self.set_trace(frame)
        return self.trace_dispatch

    def user_breakpoint(self, frame):
        print("Breakpoint reached at line", frame.f_lineno)

# Instantiate the debugger
debugger = MyDebugger()

# Set a breakpoint
debugger.set_break(5)  # Break at line 5

# Run your Python program
debugger.run('path_to_your_script.py')

In this example, the MyDebugger class subclasses bdb.Bdb and overrides the user_line and user_breakpoint methods to define custom behavior when a line is executed or a breakpoint is reached, respectively. The set_break method sets a breakpoint at a specific line number.

To use the debugger, you create an instance of your custom debugger class and call its run method, passing the path to the Python script you want to debug as an argument.

Please note that this is just a basic example, and the “bdb” module provides more advanced capabilities for implementing a full-featured debugger. You can refer to the Python documentation for more information on the “bdb” module and its available methods and classes.

This module provides a framework for debuggers. You can use this to create your own custom debuggers.

To implement custom behavior, subclass the Bdb class, and override the user methods (which are called whenever the debugger stops). To control the debugger, use the various set methods.

Example: Using the bdb module

# File: bdb-example-1.py

import bdb
import time

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

def egg(n):
    spam(n)
    spam(n)
    spam(n)
    spam(n)

def test(n):
    egg(n)

class myDebugger(bdb.Bdb):

    run = 0

    def user_call(self, frame, args):
        name = frame.f_code.co_name or "<unknown>"
        print "call", name, args
        self.set_continue() # continue

    def user_line(self, frame):
        if self.run:
            self.run = 0
            self.set_trace() # start tracing
        else:
            # arrived at breakpoint
            name = frame.f_code.co_name or "<unknown>"
            filename = self.canonic(frame.f_code.co_filename)
            print "break at", filename, frame.f_lineno, "in", name
        print "continue..."
        self.set_continue() # continue to next breakpoint

    def user_return(self, frame, value):
        name = frame.f_code.co_name or "<unknown>"
        print "return from", name, value
        print "continue..."
        self.set_continue() # continue

    def user_exception(self, frame, exception):
        name = frame.f_code.co_name or "<unknown>"
        print "exception in", name, exception
        print "continue..."
        self.set_continue() # continue

db = myDebugger()
db.run = 1
db.set_break("bdb-example-1.py", 7)
db.runcall(test, 1)

continue...
call egg None
call spam None
break at C:\ematter\librarybook\bdb-example-1.py 7 in spam
continue...
call spam None
break at C:\ematter\librarybook\bdb-example-1.py 7 in spam
continue...
call spam None
break at C:\ematter\librarybook\bdb-example-1.py 7 in spam
continue...
call spam None
break at C:\ematter\librarybook\bdb-example-1.py 7 in spam
continue...