New issue 2728: performance collapse with setattr in a large for-loop https://bitbucket.org/pypy/pypy/issues/2728/performance-collapse-with-setatt... biblicabeebli: Hi... I was interested in testing the performance difference between CPython's attribute assignment on class objects and dictionary key value assignment. I wrote a (bad) script to test this, ensured it was compatible and equivalent between Python 2 and 3, and ran it on CPython 2.7 and 3.6. Then, for goofs, I thought I would test it on pypy. pypy version info: pypy3.5-5.10 compiled using pyenv 1.2.0-8-g785738d running on mac os 10.11.6 clang version: Apple LLVM version 8.0.0 (clang-800.0.42.1) Target: x86_64-apple-darwin15.6.0 Thread model: posix Well, it either never finishes execution, or it takes more than 1 minute vs CPython's 0.057096 execution of that problematic for-loop on my computer. The eventual stack trace when after I hit ^C is pasted below, I therefore assume it is setattr that is causing the issue. Note: I tested both the class's __setattr__ method and the built in setattr() function, both have this problem. ^C Traceback (most recent call last): File "dict_class_test.py", line 104, in <module> do(100000) # <-- takes forever??? File "dict_class_test.py", line 41, in do x.__setattr__(i_string, i)