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Python decorator that catches exceptions and logs a traceback that includes every local variable of each frame.
import os
from log_exceptions import log_exceptions
def throw_something(a1, a2):
raise Exception('Whoops!')
@log_exceptions(log_if = os.getenv('MYAPP_DEBUG') is not None)
def my_function(arg1, arg2):
throw_something(arg1 + 24, arg2 - 24)
my_function(5, 6)
import types
import inspect
import sys
# default frame template (see log_exceptions below)
LOG_FRAME_TPL = ' File "%s", line %i, in %s\n %s\n'
# default value-to-string conversion function. makes sure any newlines are
# replaced with newline literals.
def log_to_str(v):
if isinstance(v, types.StringType):
return ["'", v.replace('\n', '\\n'), "'"].join('')
return str(v).replace('\n', '\\n')
# log_exceptions decorator
def log_exceptions(log_path = 'exceptions.log',
frame_template = LOG_FRAME_TPL,
value_to_string = log_to_str,
log_if = True):
A decorator that catches any exceptions thrown by the decorated function and
logs them along with a traceback that includes every local variable of every
Caught exceptions are re-raised.
log_file_name (string): a path to the log file. Defaults to
frame_template (string): a format string used to format frame information.
The following format arguments will be used when
printing a frame:
* (string) The name of the file the frame belongs
* (int) The line number on which the frame was
* (string) The name of the function the frame
belongs to.
* (string) The python code of the line where the
frame was created.
The default frame template outputs frame info as
it appears in normal python tracebacks.
value_to_string (function): a function that converts arbitrary values to
strings. The default converter calls str() and
replaces newlines with the newline literal.
This function MUST NOT THROW.
log_if (bool): a flag that can disable logging. This argument can be used
to disable/enable logging in specific situations. For
example, it can be set to the result of:
os.getenv('MYAPP_DEBUG') is not None
to make sure logging is only performed when the MYAPP_DEBUG
environment variable is defined.
A decorator that catches and logs exceptions thrown by decorated functions.
Nothing. The decorator will re-raise any exception caught by the decorated
def decorator(func):
def wrapper(*args, **kwds):
# this variable is never used. it exists so we can detect if a frame is
# referencing this specific function.
__lgw_marker_local__ = 0
return func(*args, **kwds)
except Exception, e:
if not log_if:
log_file = open(log_path, 'a')
# log exception information first in case something fails below
log_file.write('Exception thrown, %s: %s\n' % (type(e), str(e)))
# iterate through the frames in reverse order so we print the
# most recent frame first
frames = inspect.getinnerframes(sys.exc_info()[2])
for frame_info in reversed(frames):
f_locals = frame_info[0].f_locals
# if there's a local variable named __lgw_marker_local__, we assume
# the frame is from a call of this function, 'wrapper', and we skip
# it. Printing these frames won't help determine the cause of an
# exception, so skipping it reduces clutter.
if '__lgw_marker_local__' in f_locals:
# log the frame information
log_file.write(frame_template %
(frame_info[1], frame_info[2], frame_info[3], frame_info[4][0].lstrip()))
# log every local variable of the frame
for k, v in f_locals.items():
log_file.write(' %s = %s\n' % (k, value_to_string(v)))
return wrapper
return decorator
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pppigrui commented Apr 23, 2019


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