1  #!/usr/bin/env python3
       2  
       3  """
       4  A demonstration of classes and their special methods in Python.
       5  """
       6  
       7  class ESC[4;38;5;81mVec:
       8      """A simple vector class.
       9  
      10      Instances of the Vec class can be constructed from numbers
      11  
      12      >>> a = Vec(1, 2, 3)
      13      >>> b = Vec(3, 2, 1)
      14  
      15      added
      16      >>> a + b
      17      Vec(4, 4, 4)
      18  
      19      subtracted
      20      >>> a - b
      21      Vec(-2, 0, 2)
      22  
      23      and multiplied by a scalar on the left
      24      >>> 3.0 * a
      25      Vec(3.0, 6.0, 9.0)
      26  
      27      or on the right
      28      >>> a * 3.0
      29      Vec(3.0, 6.0, 9.0)
      30  
      31      and dot product
      32      >>> a.dot(b)
      33      10
      34  
      35      and printed in vector notation
      36      >>> print(a)
      37      <1 2 3>
      38  
      39      """
      40  
      41      def __init__(self, *v):
      42          self.v = list(v)
      43  
      44      @classmethod
      45      def fromlist(cls, v):
      46          if not isinstance(v, list):
      47              raise TypeError
      48          inst = cls()
      49          inst.v = v
      50          return inst
      51  
      52      def __repr__(self):
      53          args = ', '.join([repr(x) for x in self.v])
      54          return f'{type(self).__name__}({args})'
      55  
      56      def __str__(self):
      57          components = ' '.join([str(x) for x in self.v])
      58          return f'<{components}>'
      59  
      60      def __len__(self):
      61          return len(self.v)
      62  
      63      def __getitem__(self, i):
      64          return self.v[i]
      65  
      66      def __add__(self, other):
      67          "Element-wise addition"
      68          v = [x + y for x, y in zip(self.v, other.v)]
      69          return Vec.fromlist(v)
      70  
      71      def __sub__(self, other):
      72          "Element-wise subtraction"
      73          v = [x - y for x, y in zip(self.v, other.v)]
      74          return Vec.fromlist(v)
      75  
      76      def __mul__(self, scalar):
      77          "Multiply by scalar"
      78          v = [x * scalar for x in self.v]
      79          return Vec.fromlist(v)
      80  
      81      __rmul__ = __mul__
      82  
      83      def dot(self, other):
      84          "Vector dot product"
      85          if not isinstance(other, Vec):
      86              raise TypeError
      87          return sum(x_i * y_i for (x_i, y_i) in zip(self, other))
      88  
      89  
      90  def test():
      91      import doctest
      92      doctest.testmod()
      93  
      94  test()