[Python-ideas] 80 character line width vs. something wider

[Cesare Di Mauro]

Ben Finney <ben+python at benfinney.id.au> wrote:

> Aaron Rubin <aaron.rubin at 4dtechnology.com>
> writes:
>
>> Regarding this and the other notion of 5 or 6 being the proper level of
>> indentation:
>>
>> class a(object):
>>     def method1(simulation=False):
>>         try:
>>             if simulation:
>>                 for x in range(10):
>>                     if x>5:
>>                         try:
>>                             # here might begin some actual math, with two or
>> three more levels of logic, interfacing with other libraries such as NumPy,
>> etc. where you might need specific error handling
>>         except CustomError:
>>             # customer error handling
>
> This is fairly clearly a contrived example. Can you give an example of
> actual in-use code which suffers from such deep indentation?
>

>From threading.py:

class Thread(_Verbose):
    def __bootstrap_inner(self):
        try:
            self.__ident = _get_ident()
            self.__started.set()
            _active_limbo_lock.acquire()
            _active[self.__ident] = self
            del _limbo[self]
            _active_limbo_lock.release()
            if __debug__:
                self._note("%s.__bootstrap(): thread started", self)

            if _trace_hook:
                self._note("%s.__bootstrap(): registering trace hook", self)
                _sys.settrace(_trace_hook)
            if _profile_hook:
                self._note("%s.__bootstrap(): registering profile hook", self)
                _sys.setprofile(_profile_hook)

            try:
                self.run()
            except SystemExit:
                if __debug__:
                    self._note("%s.__bootstrap(): raised SystemExit", self)
            except:
                if __debug__:
                    self._note("%s.__bootstrap(): unhandled exception", self)
                # If sys.stderr is no more (most likely from interpreter
                # shutdown) use self.__stderr.  Otherwise still use sys (as in
                # _sys) in case sys.stderr was redefined since the creation of
                # self.
                if _sys:
                    _sys.stderr.write("Exception in thread %s:\n%s\n" %
                                      (self.name, _format_exc()))
                else:
                    # Do the best job possible w/o a huge amt. of code to
                    # approximate a traceback (code ideas from
                    # Lib/traceback.py)
                    exc_type, exc_value, exc_tb = self.__exc_info()
                    try:
                        print>>self.__stderr, (
                            "Exception in thread " + self.name +
                            " (most likely raised during interpreter shutdown):")
                        print>>self.__stderr, (
                            "Traceback (most recent call last):")
                        while exc_tb:
                            print>>self.__stderr, (
                                '  File "%s", line %s, in %s' %
                                (exc_tb.tb_frame.f_code.co_filename,
                                    exc_tb.tb_lineno,
                                    exc_tb.tb_frame.f_code.co_name))
                            exc_tb = exc_tb.tb_next
                        print>>self.__stderr, ("%s: %s" % (exc_type, exc_value))
                    # Make sure that exc_tb gets deleted since it is a memory
                    # hog; deleting everything else is just for thoroughness
                    finally:
                        del exc_type, exc_value, exc_tb
            else:
                if __debug__:
                    self._note("%s.__bootstrap(): normal return", self)
            finally:
                # Prevent a race in
                # test_threading.test_no_refcycle_through_target when
                # the exception keeps the target alive past when we
                # assert that it's dead.
                self.__exc_clear()
        finally:
            with _active_limbo_lock:
                self.__stop()
                try:
                    # We don't call self.__delete() because it also
                    # grabs _active_limbo_lock.
                    del _active[_get_ident()]
                except:
                    pass


Cheers,
Cesare