缺少dict键的Pythonic方式 [英] Pythonic way for missing dict keys

问题描述

大家好！


我很确定这次已被问过几次，但我好像不会在b
上找到它档案（谷歌似乎有几个问题

最近）。


我想知道什么是处理失踪的最pythonic方式

键和默认值。


根据我的读数，可以采取以下方法：


1 /检查之前（这个有一个特定的名字和首字母缩略词，我还没有用心去学习b $ b。


如果不是my_dict.has_key（键）：

my_obj = myobject（）

my_dict [key] = my_obj

else：

my_obj = my_dict [key]


2 /尝试并在出错时做出反应（这也有一个特定的名称，但是......）


尝试：

my_obj = my_dict [key]

除了AttributeError：

my_obj = myobject（）

my_dict [key] = my_obj


3 / dict.get用法：


my_obj = my_dict.get（key，myobject（））


我想知道哪一个是最推荐的方式？得到的用法似乎是最简单的，但是我看到的唯一问题是我认为myobject（）是在调用时评估的
，所以如果初始化很昂贵你

可能会看到惊喜。


提前感谢，

../alex

-

..w（the_mindstorm）p。

Hi all!

I am pretty sure this has been asked a couple of times, but I don''t seem
to find it on the archives (Google seems to have a couple of problems
lately).

I am wondering what is the most pythonic way of dealing with missing
keys and default values.

According to my readings one can take the following approaches:

1/ check before (this has a specific name and acronym that I haven''t
learnt yet by heart)

if not my_dict.has_key(key):
my_obj = myobject()
my_dict[key] = my_obj
else:
my_obj = my_dict[key]

2/ try and react on error (this has also a specific name, but...)

try:
my_obj = my_dict[key]
except AttributeError:
my_obj = myobject()
my_dict[key] = my_obj

3/ dict.get usage:

my_obj = my_dict.get(key, myobject())

I am wondering which one is the most recommended way? get usage seems
the clearest, but the only problem I see is that I think myobject() is
evaluated at call time, and so if the initialization is expensive you
will probably see surprises.

thanks in advance,
../alex
--
..w( the_mindstorm )p.

推荐答案

2007-07-20，Alex Popescu < th *********************** @ gmail.comwrote：

On 2007-07-20, Alex Popescu <th***********************@gmail.comwrote:

大家好！


我很确定这已被问了几次，但是我好像b $ b好​​像在档案中找不到它（Google似乎我最近有几个问题。


我想知道什么是处理丢失的最pythonic方式

键和默认值。


根据我的读数，可以采取以下方法：

Hi all!

I am pretty sure this has been asked a couple of times, but I
don''t seem to find it on the archives (Google seems to have a
couple of problems lately).

I am wondering what is the most pythonic way of dealing with missing
keys and default values.

According to my readings one can take the following approaches:

还有流行的collections.defaultdict 。


通常，正常dicts的get方法就是我想要的。我只使用

默认元素字典中的隐式添加才能使用

defaultdict。


- -

Neil Cerutti

There''s also the popular collections.defaultdict.

Usually, the get method of normal dicts is what I want. I use a
defaultdict only when the implicit addition to the dictionary of
defaulted elements is what I really want.

--
Neil Cerutti

Neil Cerutti< ho ***** @ yahoo.comwrote in

news ：sl ******************* @ FIAD06.norwich.edu：

Neil Cerutti <ho*****@yahoo.comwrote in
news:sl*******************@FIAD06.norwich.edu:

2007-07-20 ，Alex Popescu< th *********************** @ gmail.comwrote：

On 2007-07-20, Alex Popescu <th***********************@gmail.comwrote:

>大家好！

我很确定这已被问了好几次，但我好像在档案馆里找不到它（Google似乎有一个<最近几个问题。

我想知道什么是处理丢失的
键和默认值的最pythonic方式。

根据我的读数可以采取以下方法：

>Hi all!

I am pretty sure this has been asked a couple of times, but I
don''t seem to find it on the archives (Google seems to have a
couple of problems lately).

I am wondering what is the most pythonic way of dealing with missing
keys and default values.

According to my readings one can take the following approaches:

还有流行的collections.defaultdict。


通常，得到诺玛的方法我的意思是我想要的。我只使用

默认元素字典中的隐式添加才能使用

defaultdict。

There''s also the popular collections.defaultdict.

Usually, the get method of normal dicts is what I want. I use a
defaultdict only when the implicit addition to the dictionary of
defaulted elements is what I really want.

这看起来最接近我的需求，但在我的情况下，默认值

涉及创建一个自定义对象实例，该实例从当前获取参数

执行上下文，所以我不太确定我可以使用它。


../alex

-

.. w（the_mindstorm）p。

This looks like the closest to my needs, but in my case the default value
involves the creation of a custom object instance that is taking parameters
from the current execution context, so I am not very sure I can use it.

../alex
--
..w( the_mindstorm )p.

版本1和2与版本3不同。后者不是
为dict增加价值。


如前所述，使用：

1 - 如果你期望dict中没有键

2 - 如果你期望dict中有钥匙

Version 1 and 2 do different thing than version 3. The latter doesn''t
add value to dict.

As it was mentioned before, use:
1 - if you expect that there''s no key in dict
2 - if you expect that there is key in dict

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