# -*- coding: utf-8 -*-
"""
A small set of utilities useful for debugging misbehaving
applications. Currently this focuses on ways to use :mod:`pdb`, the
built-in Python debugger.
"""
import sys
import time
try:
basestring
from repr import Repr
except NameError:
basestring = (str, bytes) # py3
from reprlib import Repr
try:
from typeutils import make_sentinel
_UNSET = make_sentinel(var_name='_UNSET')
except ImportError:
_UNSET = object()
__all__ = ['pdb_on_signal', 'pdb_on_exception', 'wrap_trace']
[docs]def pdb_on_signal(signalnum=None):
"""Installs a signal handler for *signalnum*, which defaults to
``SIGINT``, or keyboard interrupt/ctrl-c. This signal handler
launches a :mod:`pdb` breakpoint. Results vary in concurrent
systems, but this technique can be useful for debugging infinite
loops, or easily getting into deep call stacks.
Args:
signalnum (int): The signal number of the signal to handle
with pdb. Defaults to :mod:`signal.SIGINT`, see
:mod:`signal` for more information.
"""
import pdb
import signal
if not signalnum:
signalnum = signal.SIGINT
old_handler = signal.getsignal(signalnum)
def pdb_int_handler(sig, frame):
signal.signal(signalnum, old_handler)
pdb.set_trace()
pdb_on_signal(signalnum) # use 'u' to find your code and 'h' for help
signal.signal(signalnum, pdb_int_handler)
return
[docs]def pdb_on_exception(limit=100):
"""Installs a handler which, instead of exiting, attaches a
post-mortem pdb console whenever an unhandled exception is
encountered.
Args:
limit (int): the max number of stack frames to display when
printing the traceback
A similar effect can be achieved from the command-line using the
following command::
python -m pdb your_code.py
But ``pdb_on_exception`` allows you to do this conditionally and within
your application. To restore default behavior, just do::
sys.excepthook = sys.__excepthook__
"""
import pdb
import sys
import traceback
def pdb_excepthook(exc_type, exc_val, exc_tb):
traceback.print_tb(exc_tb, limit=limit)
pdb.post_mortem(exc_tb)
sys.excepthook = pdb_excepthook
return
_repr_obj = Repr()
_repr_obj.maxstring = 50
_repr_obj.maxother = 50
brief_repr = _repr_obj.repr
# events: call, return, get, set, del, raise
def trace_print_hook(event, label, obj, attr_name,
args=(), kwargs={}, result=_UNSET):
fargs = (event.ljust(6), time.time(), label.rjust(10),
obj.__class__.__name__, attr_name)
if event == 'get':
tmpl = '%s %s - %s - %s.%s -> %s'
fargs += (brief_repr(result),)
elif event == 'set':
tmpl = '%s %s - %s - %s.%s = %s'
fargs += (brief_repr(args[0]),)
elif event == 'del':
tmpl = '%s %s - %s - %s.%s'
else: # call/return/raise
tmpl = '%s %s - %s - %s.%s(%s)'
fargs += (', '.join([brief_repr(a) for a in args]),)
if kwargs:
tmpl = '%s %s - %s - %s.%s(%s, %s)'
fargs += (', '.join(['%s=%s' % (k, brief_repr(v))
for k, v in kwargs.items()]),)
if result is not _UNSET:
tmpl += ' -> %s'
fargs += (brief_repr(result),)
print(tmpl % fargs)
return
[docs]def wrap_trace(obj, hook=trace_print_hook,
which=None, events=None, label=None):
"""Monitor an object for interactions. Whenever code calls a method,
gets an attribute, or sets an attribute, an event is called. By
default the trace output is printed, but a custom tracing *hook*
can be passed.
Args:
obj (object): New- or old-style object to be traced. Built-in
objects like lists and dicts also supported.
hook (callable): A function called once for every event. See
below for details.
which (str): One or more attribute names to trace, or a
function accepting attribute name and value, and returning
True/False.
events (str): One or more kinds of events to call *hook*
on. Expected values are ``['get', 'set', 'del', 'call',
'raise', 'return']``. Defaults to all events.
label (str): A name to associate with the traced object
Defaults to hexadecimal memory address, similar to repr.
The object returned is not the same object as the one passed
in. It will not pass identity checks. However, it will pass
:func:`isinstance` checks, as it is a new instance of a new
subtype of the object passed.
"""
# other actions: pdb.set_trace, print, aggregate, aggregate_return
# (like aggregate but with the return value)
# TODO: test classmethod/staticmethod/property
# TODO: wrap __dict__ for old-style classes?
if isinstance(which, basestring):
which_func = lambda attr_name, attr_val: attr_name == which
elif callable(getattr(which, '__contains__', None)):
which_func = lambda attr_name, attr_val: attr_name in which
elif which is None or callable(which):
which_func = which
else:
raise TypeError('expected attr name(s) or callable, not: %r' % which)
label = label or hex(id(obj))
if isinstance(events, basestring):
events = [events]
do_get = not events or 'get' in events
do_set = not events or 'set' in events
do_del = not events or 'del' in events
do_call = not events or 'call' in events
do_raise = not events or 'raise' in events
do_return = not events or 'return' in events
def wrap_method(attr_name, func, _hook=hook, _label=label):
def wrapped(*a, **kw):
a = a[1:]
if do_call:
hook(event='call', label=_label, obj=obj,
attr_name=attr_name, args=a, kwargs=kw)
if do_raise:
try:
ret = func(*a, **kw)
except:
if not hook(event='raise', label=_label, obj=obj,
attr_name=attr_name, args=a, kwargs=kw,
result=sys.exc_info()):
raise
else:
ret = func(*a, **kw)
if do_return:
hook(event='return', label=_label, obj=obj,
attr_name=attr_name, args=a, kwargs=kw, result=ret)
return ret
wrapped.__name__ = func.__name__
wrapped.__doc__ = func.__doc__
try:
wrapped.__module__ = func.__module__
except Exception:
pass
try:
if func.__dict__:
wrapped.__dict__.update(func.__dict__)
except Exception:
pass
return wrapped
def __getattribute__(self, attr_name):
ret = type(obj).__getattribute__(obj, attr_name)
if callable(ret): # wrap any bound methods
ret = type(obj).__getattribute__(self, attr_name)
if do_get:
hook('get', label, obj, attr_name, (), {}, result=ret)
return ret
def __setattr__(self, attr_name, value):
type(obj).__setattr__(obj, attr_name, value)
if do_set:
hook('set', label, obj, attr_name, (value,), {})
return
def __delattr__(self, attr_name):
type(obj).__delattr__(obj, attr_name)
if do_del:
hook('del', label, obj, attr_name, (), {})
return
attrs = {}
for attr_name in dir(obj):
try:
attr_val = getattr(obj, attr_name)
except Exception:
continue
if not callable(attr_val) or attr_name in ('__new__',):
continue
elif which_func and not which_func(attr_name, attr_val):
continue
if attr_name == '__getattribute__':
wrapped_method = __getattribute__
elif attr_name == '__setattr__':
wrapped_method = __setattr__
elif attr_name == '__delattr__':
wrapped_method = __delattr__
else:
wrapped_method = wrap_method(attr_name, attr_val)
attrs[attr_name] = wrapped_method
cls_name = obj.__class__.__name__
if cls_name == cls_name.lower():
type_name = 'traced_' + cls_name
else:
type_name = 'Traced' + cls_name
if hasattr(obj, '__mro__'):
bases = (obj.__class__,)
else:
# need new-style class for even basic wrapping of callables to
# work. getattribute won't work for old-style classes of course.
bases = (obj.__class__, object)
trace_type = type(type_name, bases, attrs)
for cls in trace_type.__mro__:
try:
return cls.__new__(trace_type)
except Exception:
pass
raise TypeError('unable to wrap_trace %r instance %r'
% (obj.__class__, obj))
if __name__ == '__main__':
obj = wrap_trace({})
obj['hi'] = 'hello'
obj.fail
import pdb;pdb.set_trace()