blocks|key|641892|text|使用字典，并且只将可选参数设置为键值对，如果要指定它。然后使用**kwargs调用语法应用字典：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|641893|avalue+=+1
condition+=+2

kwargs+=+{}
if+condition+==+1:
++++kwargs['b']+=+3

func(avalue,+**kwargs)|code-block|syntax|javascript|641894|一个空字典(+condition+!=+1大小写)将b设置为默认值。|641895|entityMap^0|V|8|0|0|7|E|Q|1|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|C]]|D|@]|E|$]]|$1|M|3|-4|5|6|7|X|8|@]|D|@]|E|$]]]|N|$]]

Use a dictionary, and only set the optional argument as a key-value pair in that if you want to specify it. Then apply the dictionary using the <code>**kwargs</code> call syntax:

<pre><code>avalue = 1
condition = 2

kwargs = {}
if condition == 1:
 kwargs['b'] = 3

func(avalue, **kwargs)
</code></pre>

An empty dictionary (the <code>condition != 1</code> case) leaves <code>b</code> set to the default value.

blocks|key|1983316|text|这个怎么样：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1983317|def+func(a,+b=None):
++++b+=+2+if+not+b+else+b
++++print("b+=+{}".format(b))

avalue+=+1
condition+=+2
arg+=+None++#+<--+Means:+"use+default"
if+condition+==+1:
++++arg+=+3

func(avalue,+arg)++#+b+=+2|code-block|syntax|javascript|1983318|如果condition+=+1|offset|length|style|CODE|1983319|func(avalue,+arg)++#++b+=+3|1983320|以上假设您可以修改函数定义。如果不是这样的话，您必须使用**kwargs。|1983321|entityMap^0|0|0|2|D|0|0|S|8|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@$I|V|J|W|K|L]]|9|@]|A|$]]|$1|M|3|N|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|Y|8|@$I|Z|J|10|K|L]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|11|8|@]|9|@]|A|$]]]|R|$]]

How about this:

<pre><code>def func(a, b=None):
 b = 2 if not b else b
 print("b = {}".format(b))

avalue = 1
condition = 2
arg = None # &lt;-- Means: "use default"
if condition == 1:
 arg = 3

func(avalue, arg) # b = 2
</code></pre>

and if <code>condition = 1</code>:

<pre><code>func(avalue, arg) # b = 3
</code></pre>

The above assumes you can modify the function definition. If that is not the case you have to go with <code>**kwargs</code>.

blocks|key|641944|text|那麽：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|641945|def+func(a,+b=None):
++++if+not+b:
++++++++b+=+2
++++print("b+=+{}".format(b))

avalue+=+1
condition+=+2
arg+=+None++#+<--+Means:+"use+default"+
if+condition+==+1:
++++arg+=+3

func(avalue,+b=arg)|code-block|syntax|javascript|641946|然而，在这种情况下，缺省值并没有按其应有的方式使用，当您有两种不同的方法时，通常会保留默认值，其中一种方法的工作方式不同，而另一种方法则不应该用开关进行加/减：|641947|def+maths(a,b,sub=false):
++++result+=+a+%2B+b
++++if+sub:
++++++++result+=+a+-+b
++++return+result|641948|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

What about :

<pre><code>def func(a, b=None):
 if not b:
 b = 2
 print("b = {}".format(b))

avalue = 1
condition = 2
arg = None # &lt;-- Means: "use default" 
if condition == 1:
 arg = 3

func(avalue, b=arg)
</code></pre>

At this point however the default isn't really used the way it should be,
defaults are usually kept for when you have two different methods, one that works in a way that the other shouldn't for example for addition/subtraction with a switch:

<pre><code>def maths(a,b,sub=false):
 result = a + b
 if sub:
 result = a - b
 return result
</code></pre>

blocks|key|1940788|text|解决办法之一可以是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1940789|def+func(a,+b=2,+**kwargs):
++++print("b+=+{}".format(b))

avalue+=+1
condition+=+2

func(avalue,+**{}+if+condition+!=+1+else+{'b':3})|code-block|syntax|javascript|1940790|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

One of the solutions can be:

<pre><code>def func(a, b=2, **kwargs):
 print("b = {}".format(b))

avalue = 1
condition = 2

func(avalue, **{} if condition != 1 else {'b':3})
</code></pre>

blocks|key|1940795|text|Op提到函数func不能修改，所以我的建议是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1940796|def+func(a,+b=2):
++++print("b+=+{}".format(b))

avalue+=+1
condition+=+2
if+condition+==+1:
++++func(avalue,+b=3)
else:
++++func(avalue)|code-block|syntax|javascript|1940797|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Op has mentioned that the function func can't be modified so my sugguestion would be :

<pre><code>def func(a, b=2):
 print("b = {}".format(b))

avalue = 1
condition = 2
if condition == 1:
 func(avalue, b=3)
else:
 func(avalue)
</code></pre>

I am trying to write code that does not repeat itself, following the <a href="https://en.wikipedia.org/wiki/Don%27t_repeat_yourself" rel="nofollow noreferrer">DRY</a> principle.

Consider a function call with many arguments, both mandatory and optional. In some cases, I would like to specify a value for an optional argument, whereas in other cases I would like to leave that value to its default value. To simplify my problem:

<pre><code>def func(a, b=2):
 print("b = {}".format(b))

avalue = 1
condition = 2
arg = None # &lt;-- Means: "use default" 
if condition == 1:
 arg = 3

func(avalue, b=arg)
</code></pre>

Output:

<pre><code>b = None
</code></pre>

Expected output:

<pre><code>b = 2
</code></pre>

Thus, I am trying to avoid coding the function call twice like this:

<pre><code>if arg:
 func(avalue, b=arg)
else:
 func(avalue)
</code></pre>

Is it possible in Python?

How to indicate that a function should use its default value of an optional argument without omitting it?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我试图按照原则编写不重复的代码。考虑包含许多参数的函数调用，包括强制性的和可选的。在某些情况下，我希望为可选参数指定一个值，而在另一些情况下，我希望将该值保留为默认值。为了简化我的问题：def func(a, b=2):    print("b = {}".format(b))avalue = 1condition =...

问如何指示函数应该使用可选参数的默认值而不忽略它？
EN

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问如何指示函数应该使用可选参数的默认值而不忽略它？EN