SRFBN

转载自：https://blog.csdn.net/NCU_wander/article/details/105529494

 

1、**

list变量前面加星号，字典变量前面加两个星号；是将其作为参量进行传递，传递进去之后仍然保持其原字典或者list的原性质；最为常见的就是argparse模块中的参数分解。

extra= {'city':'beijing','job':'engineer'}
def f(**kw):
    kw['city'] = 'shanghai'
    for k,w in kw.items():
        print(type(k),k,w)

        if w in ['shanghai']:
            print('本次循环到了city这一环节')



f(**extra)
print(extra)
<class 'str'> city shanghai
本次循环到了city这一环节
<class 'str'> job engineer
{'city': 'beijing', 'job': 'engineer'}

 

2、dict中的__missing__用法

class NoneDict(dict):
    def __missing__(self, key):
        return None
# convert to NoneDict, which return None for missing key.
def dict_to_nonedict(opt):
    if isinstance(opt, dict):
        new_opt = dict()
        for key, sub_opt in opt.items():
            new_opt[key] = dict_to_nonedict(sub_opt)
        return NoneDict(**new_opt)
        #return new_opt
    elif isinstance(opt, list):
        return [dict_to_nonedict(sub_opt) for sub_opt in opt]
    else:
        return opt

opt = [1,2,3,4]
print(dict_to_nonedict(opt))
[1, 2, 3, 4]
opt = {'a':12, 'b':116, 'c':{'d':5, 'e':66}}
print(opt['f'])
Traceback (most recent call last):
  File "a.py", line 38, in <module>
    print(opt['f'])
KeyError: 'f'
print(dict_to_nonedict(opt))

print(dict_to_nonedict(opt)['f'])

{'a': 12, 'b': 116, 'c': {'d': 5, 'e': 66}}
None

最终的输出结果为，可以看到在最后一行直接打印一个不存在的key时，仍然可以做到返回None值而非报错；

如果不是return NoneDict而是直接return new_opt，则在在最后一行打印时会直接报错。