开源阅读_01cpythonDemo

beer

地址:https://github.com/python/cpython/blob/master/Tools/demo/beer.py

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n = 100
if sys.argv[1:]:
    n = int(sys.argv[1])
```  
更佳写法:

n = int(sys.argv[1]) if sys.argv[1:] else 100) #推荐，易懂
n = sys.argv[1:] and int(sys.argv[1]) or 100)

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## hanoi
地址:https://github.com/python/cpython/blob/master/Tools/demo/hanoi.py

if sys.argv[2:]:
    bitmap = sys.argv[2]
    # Reverse meaning of leading '@' compared to Tk
    if bitmap[0] == '@': bitmap = bitmap[1:]
    else: bitmap = '@' + bitmap
else:
    bitmap = None

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更佳写法:(一定程度上牺牲了可读性)

bitmap=None if not sys.argv[2:] else sys.argv[2][1] if sys.argv[2][0]==’@’ else ‘@’ + sys.argv[2]

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## rpythond
地址:https://github.com/python/cpython/blob/master/Tools/demo/rpythond.py

def execute(request):
stdout = sys.stdout
stderr = sys.stderr
sys.stdout = sys.stderr = fakefile = io.StringIO() #链式赋值
try:
try:
exec(request, {}, {})
except:
print()
traceback.print_exc(100) #代替print e 来输出详细的异常信息
finally:
sys.stderr = stderr # 替换回来
sys.stdout = stdout
return fakefile.getvalue()

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try except finally如果使用with的上下文管理逻辑更好  

## vector
地址:https://github.com/python/cpython/blob/master/Tools/demo/vector.py

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() #创建实例？
    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)]# 列表同位置元素减法运算
    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__ # 函数赋值，(int*自己)和（自己*int）同方法

def test():
import doctest
doctest.testmod() # 文档测试方法

test()

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## 要点

sys.stdout = sys.stderr = fakefile = io.StringIO() #链式赋值
traceback.print_exc(100) #代替print e 来输出详细的异常信息
inst = cls() #创建实例？
v = [x - y for x, y in zip(self.v, other.v)]# 列表同位置元素减法运算
rmul = mul # 函数赋值，(int自己)和（自己int）同方法
doctest.testmod() # 文档测试方法