[Bf-python] hints for optimizing python exporters, using Blender2Radiance for eg.

[Willian Padovani Germano]

Campbell Barton wrote:

> (...)
>    This can throw errors if the user has relitive paths in there 
> filename.
>    eg- an image filename may be //testures/myimage.png
>
>    os.* functions dont understand blenders // as being the cerrent file
>    dir in blender.

Yeah, stumbled upon it this weekend in a bad way (!), working on the 
scripts registration code.  Blender has a function to handle that 
(BLI_convertstringcode).  It's better to update all relevant places in 
BPython to use this function before returning a path.  Good catch, Campbell.

BTW, let me add two hints about optimization:

1) Profiling should not be underestimated.  It'll tell you exactly where 
you should attack to get better performance.  And it can be as simple as 
adding:

from Blender.Sys import time
oldtime = time()

# and in selected parts of the code, after each important section add:

newtime = Blender.sys.time()
print "some relevant string to tell you what piece was executed:",
print newtime - oldtime
oldtime = newtime

2) The ac3d exporter that will be in the next Blender got about 3 times 
faster mostly because I changed all string concatenation operations to 
faster alternatives:

# these are bad:
string1 = string1 + string2
string1 += string2

# this is faster:
string1 = "%s%s" % (string1, string2)

# this is very good:
l = []
l.append(string1)
# ... some operation to get another piece of the string
l.append(string2)
# ... some operation to get another piece of the string
l.append(string3)
# ...
# in the end use the string method str.join(sequence) to assemble the 
string:
string = "".join(l)
# e.g. if you need separated text lines, use string = "\n".join(l) instead.

If you have lots of string concatenation in loops, this can really give 
you a good speed gain.

-- 
Willian