Mostly open, read, and fstat for python2:

     ~ strace python2 -c exit 2>&1 | sort | grep "^[a-z_]*[(]" | sed -e "s/^\([a-z_]*\)[(].*/\1/" | uniq -c | sort -rn | head -n 8
        199 open
         98 read
         94 fstat
         92 stat
         68 rt_sigaction
         63 close
         27 mmap
         16 mprotect

Mostly stat, rt_sigaction, and read for python3:

     ~ strace python3 -c exit 2>&1 | sort | grep "^[a-z_]*[(]" | sed -e "s/^\([a-z_]*\)[(].*/\1/" | uniq -c | sort -rn | head -n 8
         92 stat
         68 rt_sigaction
         57 read
         54 fstat
         35 open
         35 close
         28 mmap
         24 lseek

Some of this might be noise though, it's possible that it has something to do with the installed packages, not sure exactly.