getattr()与dict查找，哪个更快? [英] getattr() versus dict lookup, which is faster?

问题描述

一个有点笨拙的最佳实践问题.我习惯使用object.__dict__[some_key]动态查找对象属性值.现在我想知道哪个更好/更快:我现在的习惯或getattr(object,some_key).如果一个更好，为什么?

A somewhat noobish, best practice question. I dynamically look up object attribute values using object.__dict__[some_key] as a matter of habit. Now I am wondering which is better/faster: my current habit or getattr(object,some_key). If one is better, why?

>>> class SomeObject:
...     pass
... 
>>> so = SomeObject()
>>> so.name = 'an_object'
>>> getattr(so,'name')
'an_object'
>>> so.__dict__['name']
'an_object'

推荐答案

使用getattr()而不是直接进入__dict__结构会更好.

You are much better off using getattr() instead of going directly to the __dict__ structure.

不是因为它更快或更慢，而是因为官方API在 all 的所有情况下都能正常工作，包括对于 not 没有__dict__的类(使用 __slots__ )，或者当对象实现 __getattr__ 或

Not because it's faster or slower, but because the official API works in all circumstances, including for classes that do not have a __dict__ (when using __slots__ for example), or when an object implements the __getattr__ or __getattribute__ hooks, or when the attribute in question is a descriptor (such as a property), or a class attribute.

如果您想知道某条python语句或技术是否比另一条更快，请使用 timeit模块来测量差异:

If you want to know if any one python statement or technique is faster than another, use the timeit module to measure the difference:

>>> import timeit
>>> class Foo(object):
...     pass
... 
>>> foo = Foo()
>>> foo.bar = 'spam'
>>> timeit.timeit("getattr(foo, 'bar')", 'from __main__ import foo')
0.2125859260559082
>>> timeit.timeit("foo.__dict__['bar']", 'from __main__ import foo')
0.1328279972076416

您可以看到直接访问__dict__的速度更快，但是getattr()的工作量更大.

You can see that directly accessing __dict__ is faster, but getattr() does a lot more work.

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