effective python 读书笔记:第21条-用只能以关键字形式指定的参数来确保代码明晰

第21条-用只能以关键字形式指定的参数来确保代码明晰

关键字参数可以通过位置参数传参

问题： 1 函数是如何接受参数的 ？

def safe_division(
        number, divisor,
        ignore_overflow=False,
        ignore_zero_division=False):

    try:
        print('no error')
        return number / divisor
    except OverflowError:
        print('ignore_overflow is {}'.format(ignore_overflow))
        if ignore_overflow:
            return 0
        else:
            print('OverflowError')
            # raise
    except ZeroDivisionError:
        print('ignore_zero_division is {}'.format(ignore_zero_division))
        if ignore_zero_division:
            return float('inf')
        else:
            print('ZeroDivisionError')
            # raise


# pass
print(safe_division(1, 10 ** 500, False, False))
print('==========')
print(safe_division(1, 10 ** 500, True, False))
print('==========')
print(safe_division(1, 0, True, True))
print('==========')
print(safe_division(1, 0, True, False))
print('==========')
# no error
# 0.0
# ==========
# no error
# 0.0
# ==========
# no error
# ignore_zero_division is True
# inf
# ==========
# no error
# ignore_zero_division is False
# ZeroDivisionError
# None
# ==========
# no error
# ignore_zero_division is True
# inf

以上写法存在的弊端为：函数定义了关键字参数，但是均可以通过位置参数与关键子参数传参，而位置参数容易导致传参错误

改进方向:必须以关键字的方式传参

#PYHTON2

def safe_division(number, divisor, **kwargs):
    ignore_overflow = kwargs.pop('ignore_overflow', False)
    ignore_zero_div = kwargs.pop('ignore_zero_division', False)
    if kwargs:
        raise TypeError('Unexpected **kwargs: %r' % kwargs)
    try:
        return number / divisor
    except OverflowError:
        if ignore_overflow:
            return 0
        else:
            return 'OverflowError'
            # raise
    except ZeroDivisionError:
        if ignore_zero_div:
            return float('inf')
        else:
            return 'ZeroDivisionError'
            # raise


print(safe_division(1, 0, ignore_overflow=True, ignore_zero_division=True))
# inf
print(safe_division(1, 10 ** 500, True, False))
# TypeError: safe_division() takes 2 positional arguments but 4 were given



#PYTHON3
# 星号 位置参数的结束标志
def safe_division(
        number, divisor, *,
        ignore_overflow=False,
        ignore_zero_division=False):
    try:
        return number / divisor
    except OverflowError:
        if ignore_overflow:
            return 0
        else:
            return 'OverflowError'
            # raise
    except ZeroDivisionError:
        if ignore_zero_division:
            return float('inf')
        else:
            return 'ZeroDivisionError'
            # raise


print(safe_division(1, 0, ignore_overflow=True, ignore_zero_division=True))
# output:
# inf


print(safe_division(1, 10 ** 500, True, False))
# output
# TypeError: safe_division() takes 2 positional arguments but 4 were given