It seems importlib does multiple stat() calls on py files:

stat("/home/antoine/cpython/opt/Lib", {st_mode=S_IFDIR|0775, st_size=12288, ...}) = 0
stat("/home/antoine/cpython/opt/Lib/_sysconfigdata.py", {st_mode=S_IFREG|0664, st_size=16032, ...}) = 0
stat("/home/antoine/cpython/opt/Lib/_sysconfigdata.py", {st_mode=S_IFREG|0664, st_size=16032, ...}) = 0
open("/home/antoine/cpython/opt/Lib/__pycache__/_sysconfigdata.cpython-33.pyc", O_RDONLY) = 3


It also does multiple stat() calls on some directories:

stat("/home/antoine/cpython/opt/build/lib.linux-x86_64-3.3", {st_mode=S_IFDIR|0775, st_size=4096, ...}) = 0
stat("/home/antoine/.local/lib/python3.3/site-packages", {st_mode=S_IFDIR|0775, st_size=4096, ...}) = 0
stat("/home/antoine/.local/lib/python3.3/site-packages", {st_mode=S_IFDIR|0775, st_size=4096, ...}) = 0
stat("/home/antoine/.local/lib/python3.3/site-packages", {st_mode=S_IFDIR|0775, st_size=4096, ...}) = 0
open("/home/antoine/.local/lib/python3.3/site-packages", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3


That said, the number of system calls issued by 3.3 at startup is now much lower than with 3.2:

$ strace ./python -Sc pass 2>&1 | wc -l
512
$ strace python3.2 -Sc pass 2>&1 | wc -l
1018