ShiftMatrix is a class that generates matrix values by shifting the zeroth row left or right length_of_row times. For example: if you initialize it with sm = ShiftMatrix([1,2,3]), sm[1] will return [3,1,2]. Only the initial list is stored, the other values are generated at runtime.
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""" An NxN matrix generated by shifting the zeroth row left or right.
Only the zeroth row is stored in memory, the rest is generated. This
cuts memory usage from NxN to a single N.
>>> shift_matrix = ShiftMatrix([1, 2, 3, 4])
>>> print shift_matrix
[1, 2, 3, 4]
[4, 1, 2, 3]
[3, 4, 1, 2]
[2, 3, 4, 1]
>>> shift_matrix = ShiftMatrix([1, 2, 3, 4])
>>> print len(shift_matrix)
16
The class works with any iterable, for example a string:
>>> shift_matrix = ShiftMatrix('Test', shift='left')
>>> print shift_matrix[1]
estT
>>> shift_matrix = ShiftMatrix('Test', shift='left')
>>> print shift_matrix[1][2]
t
"""
def __init__(self, data=None, shift='right'):
if shift in ['right','left']:
self.shift = shift
else:
raise ValueError("Shift direction must be 'right' or 'left'.")
if not data:
self.data = list()
else:
try:
iter(data)
except TypeError, e:
raise TypeError("Object is not iterable.")
self.data = data
def __getitem__(self, index):
if index > len(self.data) - 1:
raise IndexError("Object has no index %d." % index)
if self.shift == 'right':
return self.data[-index % len(self.data):] + self.data[:-index]
if self.shift == 'left':
return self.data[index:] + self.data[:index % len(self.data)]
def __len__(self):
return len(self.data)
def __str__(self):
return "\n".join(str(row) for row in self.__iter__())
def __iter__(self):
for row_index in range(len(self.data)):
yield self.__getitem__(row_index)
if __name__ == "__main__":
shift_matrix = ShiftMatrix([1,2,3],shift='left')
for row in shift_matrix:
print row
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