The crash report indicates that the operating system is a OS X 10.9 Developer Preview (which is under NDA at the moment) and that you are using the python2.7.3 from the python.org 64-bit/32-bit 2.7.3 installer.  The readline module include with that installer dynamically links with the OS-provided libedit.dylib for terminal editing functions in the interactive interpreter. I can also reproduce a similar crash using the python.org 3.3.2 installer and just by entering "print('a')" twice; no need to use round(). The problem is not reproducible on current OS X 10.8 systems. Almost certainly this is due to some incompatible change in libedit.dylib.  You should open an issue with Apple reporting the compatibility problem.  The Homebrew Python most likely is linked with its own copy of the GNU readline library rather than the system libedit.