dict.has_key（x）与'x in dict' [英] dict.has_key(x) versus 'x in dict'
问题描述
您好，
我一直在使用has_key（）方法来测试字典
是否包含某个键。最近我尝试使用''in''，例如
d = {...}
如果k在d：
...
并且发现当要进行大量的关键测试时，它似乎表现得更好。
。我还注意到has_key（）计划从未来（C）Python版本中删除
。
是否采用''in''测试方式有一个优化的实现比较
到has_key（）？这是因为has_key（）被淘汰了吗？
谢谢，
Paul
Paul Melis写道：
我一直在使用has_key（）方法来测试字典是否
包含某个键。最近我尝试使用''in''，例如
d = {...}
如果k在d：
...
并且发现当要进行大量的关键测试时，它似乎表现得更好。
。我还注意到has_key（）计划从未来（C）Python版本中删除
。
是否采用''in''测试方式有一个优化的实现比较
到has_key（）？
否，但是完整的方法调用比引擎盖下的C级别的调用要慢得多。在"运营商。
这就是为什么例如
string [：len（prefix）] ==前缀
通常要快得多
string.startswith（前缀）
以及为什么
如果字符串中有字符：
string = string.replace（字符，替换）
快于
string = string.replace（字符，替换）
如果角色大多数时间都没有，尽管事实上替换
如果找不到角色，
方法实际上并没有做什么。
< / F>
Paul Melis写道：
我一直在使用has_key（）方法测试是否
字典包含某个键。最近我尝试使用
'''''，例如
d = {...}
如果k in d：
...
如果k在d.keys（）中，则不会是确切的替代品？
问候，
Bj？
-
BOFH借口＃17：
行中的脂肪电子
Bjoern Schliessmann写道：
如果k在d.keys（）中，则不会是是确切的替代？
no。这将O（1）操作转换为O（n）操作，这将是相当愚蠢的。
< / F>
Hello,
I''ve always been using the has_key() method to test if a dictionary
contains a certain key. Recently I tried the same using ''in'', e.g.
d = { ... }
if k in d:
...
and found that it seems to perform a lot better when lots of key-tests
are to be performed. I also noticed that has_key() is scheduled to be
removed from future (C)Python versions.
Does the ''in'' way of testing have an optimized implementation compared
to has_key()? Is that the reason has_key() is being phased out?
Thanks,
Paul
Paul Melis wrote:
I''ve always been using the has_key() method to test if a dictionary
contains a certain key. Recently I tried the same using ''in'', e.g.
d = { ... }
if k in d:
...
and found that it seems to perform a lot better when lots of key-tests
are to be performed. I also noticed that has_key() is scheduled to be
removed from future (C)Python versions.
Does the ''in'' way of testing have an optimized implementation compared
to has_key()?no, but full method calls are a lot slower than the under-the-hood C-level
call used by the "in" operator.
this is why e.g.
string[:len(prefix)] == prefix
is often a lot faster than
string.startswith(prefix)
and why
if character in string:
string = string.replace(character, replacement)
is faster than
string = string.replace(character, replacement)
if the character isn''t there most of the time, despite the fact that the "replace"
method doesn''t actually do something if the character isn''t found.
</F>
Paul Melis wrote:
I''ve always been using the has_key() method to test if a
dictionary contains a certain key. Recently I tried the same using
''in'', e.g.
d = { ... }
if k in d:
...Wouldn''t be "if k in d.keys()" be the exact replacement?
Regards,
Bj?rn
--
BOFH excuse #17:
fat electrons in the lines
Bjoern Schliessmann wrote:
Wouldn''t be "if k in d.keys()" be the exact replacement?no. that would convert an O(1) operation to an O(n) operation, which
would be rather silly.
</F>
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