[THRIFT-1107] improvement for compiler-generated python for 'None' object comparisons

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 0.7
• Component/s: Python - Compiler
• Patch Info: Patch Available
• Assignee: Will Pierce
• Reporter: Will Pierce
• Created: 23/Mar/11 04:03
• Updated: 23/Mar/11 18:45
• Resolved: 23/Mar/11 18:15

Description

The python code generator produces several python statements, especially the write() methods' per-field code, that compares something to None using '!= None', when it is more efficient to use the 'is not None' expression.

From what I understand, in python it's almost always true that (x != None) == (x is not None), but the actual implementation and intent is very different. The '!= None' comparison does a by-value comparison that does much more work than an object identity 'is not None' comparison does.

The actual performance impact isn't much, but I benchmarked the performance of 'x is not None' to 'x != None' and got some interesting results. In python 2.4, 2.7 and 3.1, it's about 2-3 times as fast to use 'is not None' over '!= None'.

I'll attach a patch to switch to 'is not None', and attach a simple benchmark test script exercising 'is not None' vs. '!= None' and post the performance measurements to this ticket.

These URLs are somewhat relevant about this specific issue in general:

• http://www.python.org/dev/peps/pep-0008/ (Search for 'singletons', or scroll to 'Programming Recommendations' item 2)
• http://stackoverflow.com/questions/100732/why-is-if-not-someobj-better-than-if-someobj-none-in-python - Stack Overflow question about the same, though it veers into the cost of typecasting to bool, which isn't relevant here
• http://jaredgrubb.blogspot.com/2009/04/python-is-none-vs-none.html - a similar experience and test results that match