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| #!/usr/bin/env python3
|
| """
| A demonstration of classes and their special methods in Python.
| """
|
| class Vec:
| """A simple vector class.
|
| Instances of the Vec class can be constructed from numbers
|
| >>> a = Vec(1, 2, 3)
| >>> b = Vec(3, 2, 1)
|
| added
| >>> a + b
| Vec(4, 4, 4)
|
| subtracted
| >>> a - b
| Vec(-2, 0, 2)
|
| and multiplied by a scalar on the left
| >>> 3.0 * a
| Vec(3.0, 6.0, 9.0)
|
| or on the right
| >>> a * 3.0
| Vec(3.0, 6.0, 9.0)
| """
| def __init__(self, *v):
| self.v = list(v)
|
| @classmethod
| def fromlist(cls, v):
| if not isinstance(v, list):
| raise TypeError
| inst = cls()
| inst.v = v
| return inst
|
| def __repr__(self):
| args = ', '.join(repr(x) for x in self.v)
| return 'Vec({})'.format(args)
|
| def __len__(self):
| return len(self.v)
|
| def __getitem__(self, i):
| return self.v[i]
|
| def __add__(self, other):
| # Element-wise addition
| v = [x + y for x, y in zip(self.v, other.v)]
| return Vec.fromlist(v)
|
| def __sub__(self, other):
| # Element-wise subtraction
| v = [x - y for x, y in zip(self.v, other.v)]
| return Vec.fromlist(v)
|
| def __mul__(self, scalar):
| # Multiply by scalar
| v = [x * scalar for x in self.v]
| return Vec.fromlist(v)
|
| __rmul__ = __mul__
|
|
| def test():
| import doctest
| doctest.testmod()
|
| test()
|
|
