start pdb from within a script:
import pdb;pdb.set_trace()
start pdb from the commandline:
python -m pdb <file.py>
h(elp) print available commands.
h(elp) command print help about command.
q(quit) quit debugger.
p(rint) expr print the value of expr.
pp expr pretty-print the value of expr.
w(here) print current position (including stack trace).
l(ist) list 11 lines of code around the current line.
l(ist) first, last list from first to last line number.
a(rgs) print the args of the current function.
<ENTER> repeat the last command.
n(ext) execute the current statement (step over).
s(tep) execute and step into function.
r(eturn) continue execution until the current function returns.
c(ontinue) continue execution until a breakpoint is encountered.
u(p) move one level up in the stack trace.
credits : https://github.com/nblock/pdb-cheatsheet