[MERGE] Improve decorators when necessary

[John Arbash Meinel]

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Martin Pool wrote:
...

>> In testing the difference is 300ms for bzr --version with the new
>> decorators versus 270ms without them. So the fact that they add 30ms to
>> startup time is significant, and worth the effort of avoiding it.
> 
> Very nice.
> 
>> -def needs_read_lock(unbound):
>> +
>> +def _get_parameters(func):
>> +    """Recreate the parameters for a function using introspection.
>> +
>> +    :return: (function_params, passed_params)
>> +        function_params is the list of parameters to the original function.
>> +        This is something like "a, b, c=None, d=1"
>> +        passed_params is how you would pass the parameters to a new function.
>> +        This is something like "a=a, b=b, c=c, d=d"
>> +    """
> 
> When I first read the docstring, it was not clear to me that you were
> returning strings containing python source code, rather than a
> structured representation.

I'll clean it up. At one point it was something slightly different,
before I found the functions in 'inspect' I was doing it all manually.

> 
>> +    global _inspect
>> +    if _inspect is None:
>> +        import inspect
>> +        _inspect = inspect
> 
> Is this to avoid the overhead of running the import statement each time
> this method is entered?

That was the thought. I have a few options:

1) 'import inspect' at the top. The problem is inspect is one of the
files we *don't* want if we can help it. (Hence the
'inspect_for_copy.py'  that I wrote).

2) lazy_import('import inspect'). That requires making decorators depend
on lazy_import. And I was trying to keep dependencies minimal. This
would certainly be an alternative, though.

3) 'import inspect' inside the function. I thought we found that to be a
significant overhead.

> 
> +1
> 

Thanks. I'll definitely clean up the doc before submitting. But what are
your feelings about the 'import inspect' stuff?

John
=:->
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