Why does stack.inspect take so long?

[63q2o4i02]

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 disproportionately
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]

[[email protected]]

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 disproportionately
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?

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,

import sys, inspect
def name_of_caller(): .... return inspect.getframeinfo(sys._getframe(1), context=0)[2]
def f(): .... print "my name is", name_of_caller()
f()

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]

[[email protected]]

Hi, I've written a top-down recursive decent parser for SPICE circuit
descriptions. For debugging purposes, I wanted each production ....
Any clues?

It should go much faster to use a function that doesn't crawl the
entire call stack. For example,

import sys, inspect
def name_of_caller(): ... return inspect.getframeinfo(sys._getframe(1), context=0)[2]
def f(): ... print "my name is", name_of_caller()
f()

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.

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

ms