python - 从 defaultdict 获取原始 key 集

Question

有没有办法从 defaultdict 获取原始/一致的 key 列表，即使请求的 key 不存在？

from collections import defaultdict
>>> d = defaultdict(lambda: 'default', {'key1': 'value1', 'key2' :'value2'})
>>>
>>> d.keys()
['key2', 'key1']
>>> d['bla']
'default'
>>> d.keys() # how to get the same: ['key2', 'key1']
['key2', 'key1', 'bla']

Answer 1

你必须排除。具有默认值的键!

>>> [i for i in d if d[i]!=d.default_factory()]
['key2', 'key1']

与 Jean 建议的方法的时间比较，

>>> def funct(a=None,b=None,c=None):
...     s=time.time()
...     eval(a)
...     print time.time()-s
...
>>> funct("[i for i in d if d[i]!=d.default_factory()]")
9.29832458496e-05
>>> funct("[k for k,v in d.items() if v!=d.default_factory()]")
0.000100135803223
>>> ###storing the default value to a variable and using the same in the list comprehension reduces the time to a certain extent!
>>> defa=d.default_factory()
>>> funct("[i for i in d if d[i]!=defa]")
8.82148742676e-05
>>> funct("[k for k,v in d.items() if v!=defa]")
9.79900360107e-05