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POCalling a Python function with *args,**kwargs and optional / default arguments
 

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  1. POCalling a Python function with *args,**kwargs and optional / default arguments
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    <p>In python, I can define a function as follows:</p> <pre><code>def func(kw1=None,kw2=None,**kwargs): ... </code></pre> <p>In this case, i can call func as:</p> <pre><code>func(kw1=3,kw2=4,who_knows_if_this_will_be_used=7,more_kwargs=Ellipsis) </code></pre> <p>I can also define a function as:</p> <pre><code>def func(arg1,arg2,*args): ... </code></pre> <p>which can be called as</p> <pre><code>func(3,4,additional,arguments,go,here,Ellipsis) </code></pre> <p>Finally, I can combine the two forms</p> <pre><code>def func(arg1,arg2,*args,**kwargs): ... </code></pre> <p>But, what does not work is calling:</p> <pre><code>func(arg1,arg2,*args,kw1=None,kw2=None,**kwargs): #SYNTAX ERROR (in python 2 only, apparently this works in python 3) ... </code></pre> <p>My original thought was that this was probably because a function</p> <pre><code>def func(arg1,arg2,*args,kw1=None): ... </code></pre> <p>can be called as</p> <pre><code>func(1,2,3) #kw1 will be assigned 3 </code></pre> <p>So this would introduce some ambiguity as to whether 3 should be packed into args or kwargs. However, with python 3, there is the ability to specify keyword only arguments:</p> <pre><code>def func(a,b,*,kw=None): #can be called as func(1,2), func(1,2,kw=3), but NOT func(1,2,3) ... </code></pre> <p>With this, it seems that there is no syntactic ambiguity with:</p> <pre><code>def func(a,b,*args,*,kw1=None,**kwargs): ... </code></pre> <p>However, this still brings up a syntax error (tested with Python3.2). Is there a reason for this that I am missing? And, is there a way to get the behavior I described above (Having *args with default arguments) -- I know I can simulate that behavior by manipulating the kwargs dictionary inside the function.</p>
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    1. COno idea why you got syntax error for "def func(arg1,arg2,*args,kw1=None,kw2=None,**kwargs):"
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    2. CO@okm Because I didn't test that version on python 3, only python 2. I just assumed the final version would work, and when It didn't, I assumed the previous versions wouldn't work either. Thanks!.
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    3. COHow should a bare `3` ever get into `kwargs`? What keyword would it use? I cannot see any ambiguity. Note that the bare `*` in the argument list is only useful if there's no `*args`. It's a placeholder you use *instead* of `*args`.
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      1. USSven Marnach
 

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