75 lines
1.5 KiB
Python
75 lines
1.5 KiB
Python
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#!/usr/bin/env python3
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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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"""
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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 'Vec({})'.format(args)
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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 test():
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import doctest
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doctest.testmod()
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test()
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