mirror of https://github.com/python/cpython
95 lines
1.8 KiB
Python
Executable File
95 lines
1.8 KiB
Python
Executable File
#!/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()
|