def test_all_blanks(self):
t = Tape()
t.shift_left()
t.shift_left()
t.shift_left()
t.shift_left()
self.assertEqual(t.read(), 0)
t2 = Tape()
t2.shift_right()
t2.shift_right()
t2.shift_right()
t2.shift_right()
self.assertEqual(t2.read(), 0)
def test_different_blank_symbol(self):
t = Tape(blank_symbol=None)
self.assertEqual(t.read(), None)
t.shift_left()
t.shift_left()
t.shift_left()
t.shift_left()
self.assertEqual(t.read(), None)
t2 = Tape(blank_symbol=None)
t2.shift_right()
t2.shift_right()
t2.shift_right()
t2.shift_right()
self.assertEqual(t2.read(), None)
class System(object):
def __init__(self, machine, tape=None):
"""
Requires a machine instance, and defaults to the
default tape is not supllied with one.
"""
self.machine = machine
if tape is None:
self.tape = Tape()
else:
self.tape = tape
self.steps = 0
def next(self):
"""
Allows the machine to proceed one step forward
"""
self.steps += 1
write_symbol, shift_right = self.machine.next(self.tape.read())
self.tape.write(write_symbol)
if shift_right:
self.tape.shift_right()
else:
self.tape.shift_left()
def iterate_until_halt(self, max_steps=None):
"""
Iterates the machine until it halts. If max_step is supplied and
reached before a halt occurs, DidNotHalt exception is raised.
"""
while True:
try:
self.next()
except Halt:
return self.steps
if max_steps is not None and self.steps >= max_steps:
raise DidNotHalt()
def get_state_tape_contents_and_head_index(self):
tape_contents, head_index = self.tape.get_contents_and_index()
return self.machine.state, tape_contents, head_index
def test_write_shift(self):
t = Tape()
t.write(1)
t.shift_left()
self.assertEqual(t.read(), 0)
t.shift_right()
self.assertEqual(t.read(), 1)
t.shift_right()
self.assertEqual(t.read(), 0)
t.write(2)
t.shift_right()
t.shift_left()
self.assertEqual(t.read(), 2)
t.shift_left()
self.assertEqual(t.read(), 1)
def test_get_contents_and_index_write_shfit(self):
t = Tape()
t.write(1)
t.shift_left()
t.write(2)
t.shift_left()
t.shift_right()
t.shift_right()
t.shift_right()
t.shift_right()
t.write(3)
t.shift_right()
t.shift_left()
t.shift_left()
tape_contents, index = t.get_contents_and_index()
self.assertEqual(tape_contents, [2,1,0,3])
self.assertEqual(index, 2)
