概述
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']
>>> [i for i in d if d[i]!=d.default_factory()] ['key2','key1']
时间与Jean建议的方法比较,
>>> 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
总结
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