DIY stuffs for the first steps of Python pdb, summarized from https://pymotw.com/3/pdb

cheatsheet-pdb.md

Starting the Debugger

From the command line

$ python3 -m pdb myscript.py  

Within the interpreter

$ python3

>>> import pdb
>>> import myscript
>>> pdb.run('myscript.MyObj(5).mymethod()')

From within a program

Add pdb.set_trace() anywhere you want to start debugging and then run it.

$ python3 myscript.py

After a failure

Run pdb.pm() after an error raised

Controlling the Debugger

Navigating the execution stack

• where or w: shows the current line and tree
• list or l: shows more context around the current location
• longlist or ll: shows the entire function or frame which contains the current location
• source OBJ: shows the source of OBJ
• up and down: moves between frames towards older and newer stack, respectively

Examining variables on the stack

• Just type existing variables to check it out.
• print(VAR) or p VAR: print a variable VAR
• prettyprint or pp: pretty print
• !{expression}: run expression within the interpreter (it can change the value of a variable)
• interact: dive into "interactive mode" and <CTRL-D> for exiting the interactive prompt

Stepping through a program

• step: execute the line and step into if there is, otherwise move next
• next: execute the line and move next
• until: execute until it progresses to the next line (e.g. run through a loop)
• return: execute until the return line of a function

Breakpoints

• break #LINENO: set a breakpoint to #LINENO line
• continue or c: execute until the next breakpoint
• break FILENAME:LINENO: set a breakpoint to LINENO of another FILENAME
• break: list current breakpoints set

Managing breakpoints

• break OBJNAME: set a breakpoint to OBJNAME
• disable #BREAKPOINT: disable the breakpoint #BREAKPOINT
• enable #BREAKPOINT: enable the breakpoint #BREAKPOINT
• clear #BREAKPOINT: delete the breakpoint #BREAKPOINT

Temporary breakpoints

• tbreak: it hits only once

Conditional breakpoints

• break #LINENO, {conditional expression}
• `condition #BREAKPOINT {conditional expression}': gives the condition to the specified breakpoint

Ignoring breakpoints

• ignore #BREAKPOINT #HITNUMBER: the specified breakpoint will only hit #HITNUMBER times and then be ignored
• ignore #BREAKPOINT 0: re-activate

Triggering actions on a breakpoint

• command #BREAKPOINT: register a custom command for the specified breakpoint (debugger prompt changes from (Pdb) to (com)

Watching data change

• display VAR
• display: list current variables to be displayed
• undisplay VAR

Changing Execution Flow

Jump ahead

• jump #LINENO: skip to #LINENO line if #CURRENT < #LINENO, otherwise jump back

Restarting a program

$ python3 -m pdb myscript.py
# works are done
(pdb)

• run ARGS: restart myscript.py with arguments ARGS(space-separated text)

Customizing the Debugger with Aliases

• alias ALIAS COMMAND: ALIAS <- COMMAND
• alias: list all aliases
• alias ALIAS: show information of ALIAS
• COMMAND can take numbered arguments as format %n, %* consumes all arguments
• unalias ALIAS: delete the alias

Saving Configuration Settings

Write your .pdbrc