Why does stack.inspect take so long?

[63q2o4i02@sneakemail.com]

Hi, I've written a top-down recursive decent parser for SPICE circuit
descriptions. For debugging purposes, I wanted each production
rule/function to know what its own name was, so at the beginning of
each rule/function, I make a call to inspect.stack()[0][3] (I think...)
and that fetches the name from someplace. However, with a bunch of
test text input, this takes ~10 seconds to run. When I comment out the
inspect.stack() function from each production/function, the program
speeds up to 0.04s, or 250x !! I loaded up the profiler to see what
was there, and although I don't understand the output entirely, it
looks like the stack frame functions are used in disproportionat ely
large amounts compared to other often-used functions. This is a
*recursive* parser, so it's being called a lot even for simple things.
I'm wondering still why there is a 250x speed up when I comment it out.
Any clues?

thanks
ms

[Tim Peters]

Re: Why does stack.inspect take so long?

[63q2o4i02@sneak email.com][color=blue]
> Hi, I've written a top-down recursive decent parser for SPICE circuit
> descriptions. For debugging purposes, I wanted each production
> rule/function to know what its own name was, so at the beginning of
> each rule/function, I make a call to inspect.stack()[0][3] (I think...)
> and that fetches the name from someplace. However, with a bunch of
> test text input, this takes ~10 seconds to run. When I comment out the
> inspect.stack() function from each production/function, the program
> speeds up to 0.04s, or 250x !! I loaded up the profiler to see what
> was there, and although I don't understand the output entirely, it
> looks like the stack frame functions are used in disproportionat ely
> large amounts compared to other often-used functions. This is a
> *recursive* parser, so it's being called a lot even for simple things.
> I'm wondering still why there is a 250x speed up when I comment it out.
> Any clues?[/color]

Look at the source code (inspect.py, function `stack()`). It
obviously takes time proportional to the total depth of the call
stack, and for a recursive-descent parser that's likely to be highly
non-trivial most of the time.

It should go much faster to use a function that doesn't crawl the
entire call stack. For example,
[color=blue][color=green][color=darkred]
>>> import sys, inspect
>>> def name_of_caller( ):[/color][/color][/color]
.... return inspect.getfram einfo(sys._getf rame(1), context=0)[2][color=blue][color=green][color=darkred]
>>> def f():[/color][/color][/color]
.... print "my name is", name_of_caller( )[color=blue][color=green][color=darkred]
>>> f()[/color][/color][/color]
my name is f

name_of_caller( ) takes time independent of the call-stack depth.

The "context=0" is to avoid wasting time sucking up and packaging
source-code lines you don't want anyway.

[63q2o4i02@sneakemail.com]

Re: Why does stack.inspect take so long?


Tim Peters wrote:[color=blue]
> [63q2o4i02@sneak email.com][color=green]
> > Hi, I've written a top-down recursive decent parser for SPICE circuit
> > descriptions. For debugging purposes, I wanted each production[/color][/color]
....[color=blue][color=green]
> > Any clues?[/color]
>[/color]
[color=blue]
> It should go much faster to use a function that doesn't crawl the
> entire call stack. For example,
>[color=green][color=darkred]
> >>> import sys, inspect
> >>> def name_of_caller( ):[/color][/color]
> ... return inspect.getfram einfo(sys._getf rame(1), context=0)[2][color=green][color=darkred]
> >>> def f():[/color][/color]
> ... print "my name is", name_of_caller( )[color=green][color=darkred]
> >>> f()[/color][/color]
> my name is f
>
> name_of_caller( ) takes time independent of the call-stack depth.
>
> The "context=0" is to avoid wasting time sucking up and packaging
> source-code lines you don't want anyway.[/color]


Cool, thanks. I'll try that. I didn't realize there were other ways
of getting it.

ms