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""" |
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A demonstration of classes and their special methods in Python. |
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""" |
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class Vec: |
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"""A simple vector class. |
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Instances of the Vec class can be constructed from numbers |
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>>> a = Vec(1, 2, 3) |
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>>> b = Vec(3, 2, 1) |
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added |
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>>> a + b |
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Vec(4, 4, 4) |
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subtracted |
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>>> a - b |
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Vec(-2, 0, 2) |
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and multiplied by a scalar on the left |
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>>> 3.0 * a |
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Vec(3.0, 6.0, 9.0) |
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or on the right |
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>>> a * 3.0 |
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Vec(3.0, 6.0, 9.0) |
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and dot product |
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>>> a.dot(b) |
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10 |
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and printed in vector notation |
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>>> print(a) |
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<1 2 3> |
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""" |
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def __init__(self, *v): |
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self.v = list(v) |
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@classmethod |
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def fromlist(cls, v): |
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if not isinstance(v, list): |
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raise TypeError |
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inst = cls() |
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inst.v = v |
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return inst |
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def __repr__(self): |
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args = ', '.join([repr(x) for x in self.v]) |
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return f'{type(self).__name__}({args})' |
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def __str__(self): |
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components = ' '.join([str(x) for x in self.v]) |
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return f'<{components}>' |
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def __len__(self): |
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return len(self.v) |
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def __getitem__(self, i): |
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return self.v[i] |
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def __add__(self, other): |
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"Element-wise addition" |
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v = [x + y for x, y in zip(self.v, other.v)] |
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return Vec.fromlist(v) |
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def __sub__(self, other): |
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"Element-wise subtraction" |
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v = [x - y for x, y in zip(self.v, other.v)] |
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return Vec.fromlist(v) |
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def __mul__(self, scalar): |
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"Multiply by scalar" |
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v = [x * scalar for x in self.v] |
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return Vec.fromlist(v) |
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__rmul__ = __mul__ |
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def dot(self, other): |
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"Vector dot product" |
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if not isinstance(other, Vec): |
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raise TypeError |
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return sum(x_i * y_i for (x_i, y_i) in zip(self, other)) |
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def test(): |
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import doctest |
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doctest.testmod() |
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test() |
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