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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)
and dot product
>>> a.dot(b)
10
and printed in vector notation
>>> print(a)
<1 2 3>
"""
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 f'{type(self).__name__}({args})'
def __str__(self):
components = ' '.join([str(x) for x in self.v])
return f'<{components}>'
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 dot(self, other):
"Vector dot product"
if not isinstance(other, Vec):
raise TypeError
return sum(x_i * y_i for (x_i, y_i) in zip(self, other))
def test():
import doctest
doctest.testmod()
test()
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