2013/3/20 anatoly techtonik <[email protected]>
> On Wed, Mar 20, 2013 at 7:36 PM, Amaury Forgeot d'Arc
> <[email protected]>wrote:
>
>> 2013/3/20 anatoly techtonik <[email protected]>
>>
>>> On Wed, Mar 20, 2013 at 5:28 PM, Amaury Forgeot d'Arc <
>>> [email protected]> wrote:
>>>
>>>> 2013/3/20 anatoly techtonik <[email protected]>
>>>>
>>>>> Hi,
>>>>>
>>>>> I've created a module to dump function trace during execution of
>>>>> Python script. You can see session example in attachment. The format is of
>>>>> PHP Xdebug tool [2] just because I had some scripts from the past to
>>>>> analyze it.
>>>>>
>>>>> The module uses sys.settrace() to analyse frames in 'call' events with
>>>>> callback(frame, event, arg).
>>>>>
>>>>> Recently I've got an anonymous report that some frame misses filename
>>>>> information when run under IDE:
>>>>>
>>>>> https://bitbucket.org/techtonik/xtrace/issue/2/use-of-xtrace-module-within-ide-causes
>>>>>
>>>>> There is unlikely to be any more feedback from the user to make me
>>>>> understand and reproduce the behavior, nor there is a sufficient
>>>>> documentation in sys.trace description [1]. So I am on my own. But I can
>>>>> not read C code the CPython is written in, so I ask here.
>>>>>
>>>>> What are possible execution contexts for Python?
>>>>> How each execution context affects data structure that is passed to
>>>>> trace function (frame and arg)?
>>>>>
>>>>
>>>> It's simpler than that: when running from an interactive session,
>>>> f_back is empty...
>>>>
>>>> >>> def trace(frame, event, arg):
>>>> ... funcname = frame.f_code.co_name
>>>> ... if funcname == '<module>':
>>>> ... print frame.f_back.f_code.co_filename
>>>> ...
>>>> >>> import sys
>>>> >>> sys.settrace(trace)
>>>> >>> 1
>>>> Traceback (most recent call last):
>>>> File "<stdin>", line 1, in <module>
>>>> File "<stdin>", line 4, in trace
>>>> AttributeError: 'NoneType' object has no attribute 'f_code'
>>>>
>>>
>>> Thanks a lot. =)
>>>
>>> User said he was using module from the IDE and at first I thought it
>>> wasn't possible to use module without previous stack frame (f_back), but I
>>> was wrong:
>>>
>>> > py -2 -s -S
>>> Python 2.7.3 (default, Apr 10 2012, 23:31:26) [MSC v.1500 32 bit
>>> (Intel)] on win32
>>> >>> import xtrace
>>> >>> xtrace.start()
>>> TRACE START [2013-03-20 18:49:27]
>>> >>> z = 0
>>> -> decode() C:\Python27\lib\encodings\cp437.py:14
>>> Traceback (most recent call last):
>>> File "<stdin>", line 1, in <module>
>>> File "xtrace.py", line 66, in function_trace_xdebug
>>> filename = self._strip_cwd(frame.f_back.f_code.co_filename)
>>> AttributeError: 'NoneType' object has no attribute 'f_code'
>>>
>>>
>>> On the way I've discovered that my Python is hacked. Without -s -S key
>>> it executes modules from local temp directory.
>>> ...
>>> -> ensure_unicode()
>>> c:\users\user\appdata\local\temp\easy_install-k8gvbp\pyreadline-1.7.1-py2.7-win32.egg.tmp\pyre
>>> dline\unicode_helper.py:20
>>> ...
>>>
>>>
>>> So there are absolutely no differences in running code in these
>>> execution contexts?
>>> - code runs from a file
>>> - code runs from a interactive console
>>>
>>
>> Of course there is a difference; the code below works run from a file,
>> but not when pasted into the interactive console:
>>
>> def trace(frame, event, arg):
>> funcname = frame.f_code.co_name
>> print frame.f_code, repr(frame.f_code.co_code), event, arg
>> if funcname == '<module>':
>> print " module", repr(frame.f_back.f_code.co_code)
>>
>> import sys
>> sys.settrace(trace)
>> exec '1 + 1'
>>
>
> For console it pretty clear why no previous frame exists - stack is
> resolved at >>> prompt. But what is this top frame that appears inside file
> context? The following code gives:
> <module> 7
> <module> 1
>
> def trace(frame, event, arg):
> print frame.f_back.f_code.co_name, frame.f_back.f_lineno
> print frame.f_code.co_name, frame.f_lineno
>
> import sys
> sys.settrace(trace)
> exec '1 + 1'
>
> How to identify the frames here? How come that 7th line of module is
> executed before 1 st? I expected to have module name available somewhere
> for <module> object. All right, this kind of tricky - '1 +1' a separate
> module, right? It is anonymous and doesn't have a name. Still is it
> possible to identify it somehow? For printing in function traces.
>
An exception traceback gives you the answer; with the script foo.py below:
def f():
exec 'x + 1'
f()
I get:
Traceback (most recent call last):
File "/tmp/foo.py", line 4, in <module>
f()
File "/tmp/foo.py", line 2, in f
exec 'x + 1'
File "<string>", line 1, in <module>
NameError: name 'x' is not defined
Do you see all the information you need here?
If yes, it's possible to extract it from the current frames.
>
>>
>>> I realize that I don't know how to set trace function for external file,
>>> so that when the file is executed, the first frame won't have the previous
>>> stack frame. I do it like so:
>>> start()
>>> execfile(script)
>>> stop()
>>>
>>
>> I'ts indeed difficult to detach the "script" from the frame running the
>> execfile statement.
>> You could handle this case specially in your trace function, though.
>>
>
> Now that I understand, I can handle it. I guess stripping the 0 level
> calls (where it will be only one) will help. Thanks again.
>
--
Amaury Forgeot d'Arc
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