The short answer is: both exit() and quit() are instances of the same Quitter class, the difference is in naming only, that must be added to increase user-friendliness of the interpreter.
For more details let’s check out the source: http://hg.python.org/cpython
In Lib/site.py (python-2.7) we see the following:
def setquit():
"""Define new builtins 'quit' and 'exit'.
These are objects which make the interpreter exit when called.
The repr of each object contains a hint at how it works.
"""
if os.sep == ':':
eof="Cmd-Q"
elif os.sep == '\\':
eof="Ctrl-Z plus Return"
else:
eof="Ctrl-D (i.e. EOF)"
class Quitter(object):
def __init__(self, name):
self.name = name
def __repr__(self):
return 'Use %s() or %s to exit' % (self.name, eof)
def __call__(self, code=None):
# Shells like IDLE catch the SystemExit, but listen when their
# stdin wrapper is closed.
try:
sys.stdin.close()
except:
pass
raise SystemExit(code)
__builtin__.quit = Quitter('quit')
__builtin__.exit = Quitter('exit')
The same logic we see in python-3.x.