pdb

pdb is the Python debugger included in Python’s standard library. It provides an interactive, text-based debugging environment for Python programs that allows stepping through code execution, inspecting variables, and analyzing program state.

Core Features

Post-mortem Debugging

• Launches debugger when unhandled exceptions occur
• Allows inspection of program state at point of failure

Interactive Debugging

• Steps through code line by line
• Sets breakpoints at specific lines
• Evaluates expressions in current context
• Modifies variables during execution

Integration Methods

• Command line with python -m pdb script.py
• Hard-coded breakpoints via breakpoint() function
• Post-mortem analysis after exceptions
• Remote debugging capabilities

Key Commands

Program Flow

• n (next): Execute next line
• s (step): Step into function call
• c (continue): Continue execution
• r (return): Continue until current function returns
• q (quit): Exit debugger

Breakpoints

• b [filename:]lineno: Set breakpoint
• clear [filename:]lineno: Remove breakpoint
• tbreak: Set temporary breakpoint
• disable: Disable breakpoint
• enable: Enable breakpoint

Inspection

• p expression: Print value of expression
• pp expression: Pretty-print value
• whatis expression: Print type of expression
• l: List source code around current line
• a: Print current function’s arguments

Limitations

• Basic text-based interface
• Limited IDE integration
• Cannot modify frozen code objects

Learn More

• Python Debugging With Pdb
• Python Debugger Documentation
• Command Reference