PDB: The Python Debugger

https://www.youtube.com/playlist?list=PLTejD6544296J48NA7-agj70__GVLpZ8J

playlist about this presentation

Johni Douglas Marangon

www.linkedin.com/in/johnidouglas

github.com/johnidm

johnidouglas.com

johni.douglas.marangon@gmail.com

Fullstack Developer at Contentools

suggestion for talks next

27. Debugging and Profiling

https://docs.python.org/3/library/debug.html

27.4. The Python Profilers

https://docs.python.org/3/library/profile.html

official documentation

27.3. pdb — The Python Debugger

https://docs.python.org/3/library/pdb.html

references
        

            

https://www.youtube.com/watch?v=P0pIW5tJrRM

https://www.youtube.com/watch?v=lnlZGhnULn4

https://www.youtube.com/watch?v=vfPtGsSJldg

http://www.onlamp.com/pub/a/python/2005/09/01/debugger.html
    
https://pymotw.com/2/pdb/
    

        

pdb

an interactive source code debugger for Python programs

invoking PDB

python -m pdb <filename>

script mode

trace mode

run mode

import pdb; pdb.set_trace()

>>> import pdb
>>> pdb.run('<module>.<func<args>>')

when reached, the debugger is started with the prompt "(Pdb)"

postmortem mode 

import pdb; pdb.pm()

try:
    # your code
except:
    import pdb, traceback, sys
    _, _, tb = sys.exc_info()
    traceback.print_exc()
    pdb.post_mortem(tb)

Enter post-mortem debugging of the given traceback object. If no traceback is given, it uses the one of the exception that is currently being handled (an exception must be being handled if the default is to be used).

basic

(h)elp | ? - list of available commands

(q)uit - quit from the debugger

(h)elp command - print help about command

<ENTER> - repeat the last command

examine code

p(rint) expr - print the value of expr

you can print multiple variables
p a, b, c
you cam omit p


pp expr - pretty print the value of expr


a(args) - print the argument list of the current function

navigate code

l(ist) – list 11 lines around the line
 + and – 5 around the line
The current line in the current frame is indicated by ->
With . as argument list lines around the current line


l(list) lineno - list starting lineno

l(list) startno, endno - list the given range

   
ll(longlist) - List all source code for the current function or frame

interactive code

n(ext) – step over next line of code

c(ont(inue)) - continue execution

s(tep) - step into function

r(eturn) - skip ahead to the 
end of the subroutine

until​ - skip over a loop

j(ump) lineno - set the next line that will be executed

traverse the stack

(w)here - print current locations on stack trace

u(p) [count] - move the current frame to up

d(own) [count] - move the current frame to down

manipulation

!stmt – A python (one-line) statement
you may change a variable value or call a function
you can omit !


declare new variables

import modules and call functions

breakpoints

b(reak) – Show list of breakpoints


b(reak) lineno – Set a breakpoint on line lineno


(cl)ear - Remove all breakpoints


(cl)ear bpno – Remove the breakpoint number in list (use b to see list of breakpoints)

enable bpno – enable the breakpoint number in list (use b to see list of breakpoints)


disable bpno –  dissalbe the breakpoint number in list (use b to see list of breakpoints)

tbreak lineno - set a temporary brackpoint
is removed when first hit


ignore bpno, counter - ingnore a breackpoint number in list ignore counter
resetting the ignore count to zero re‐ enables the breakpoint immediately ingnore 1, 0

b(reak) func - set a brackpoint at first line of func


b(reak) lineno, cond - set a brackpoint with a condicitonal


b(reak) file:lineno - set a brackpoint into file at line lineno

advanced commands 

condition bpno [condition] - set a new condition for the breakpoint

commands [bpno] - specify a list of commands for breakpoint number

alias - list all aliases

alias [name [command]] - create an alias

unalias name - delete the specified alias

Saving Configuration Settings

create a .pdbrc file in root directory

define aliases, commom brakpoints, etc

# Print instance variables (usage "pi classInst")
alias pi for k in %1.__dict__.keys(): print("%1.",k,"=",%1.__dict__[k])
# Print instance variables in self
alias ps pi self

# current user dir
alias lsd import os; print(os.path.abspath(os.path.expanduser('~')))

Other tools

rdb - http://docs.celeryproject.org/en/latest/tutorials/debugging.html

wdb - https://pypi.python.org/pypi/wdb/

ipdb - https://pypi.python.org/pypi/ipdb/

pdbpp - https://pypi.python.org/pypi/pdbpp/

rpdb - https://pypi.python.org/pypi/rpdb/

pydbgr - https://pypi.python.org/pypi/pydbgr/

pudb - https://pypi.python.org/pypi/pudb

thanks

questions?