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Date: Thu, 23 May 2013 14:52:07 -0400
From: Matthew Gilson <m.gilson1@gmail.com>
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Subject: Non-identifiers in dictionary keys for **expression syntax
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This is a question regarding the documentation around dictionary 
unpacking.  The documentation for the call syntax 
(http://docs.python.org/3/reference/expressions.html#grammar-token-call) 
says:

"If the syntax **expression appears in the function call, expression 
must evaluate to a mapping, the contents of which are treated as 
additional keyword arguments."

That's fine, but what is a keyword argument?  According to the glossary 
(http://docs.python.org/3.3/glossary.html):

/"keyword argument/: an argument preceded by an identifier (e.g. name=) 
in a function call or passed as a value in a dictionary preceded by **."

As far as I'm concerned, this leads to some ambiguity in whether the 
keys of the mapping need to be valid identifiers or not.

Using Cpython, we can do the following:

      def func(**kwargs):
           print kwargs

      d = {'foo bar baz':3}

So that might lead us to believe that the keys of the mapping do not 
need to be valid identifiers.  However, the previous function does not 
work with the following dictionary:

     d = {1:3}

because not all the keys are strings.  Is there a way to petition to get 
this more rigorously defined?

Thanks,
~Matt




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  <body text="#000000" bgcolor="#FFFFFF">
    This is a question regarding the documentation around dictionary
    unpacking.&nbsp; The documentation for the call syntax
    (<a class="moz-txt-link-freetext" href="http://docs.python.org/3/reference/expressions.html#grammar-token-call">http://docs.python.org/3/reference/expressions.html#grammar-token-call</a>)
    says:<br>
    <br>
    "If the syntax <tt class="docutils literal"><span class="pre">**expression</span></tt>
    appears in the function call, <tt class="docutils literal"><span
        class="pre">expression</span></tt> must
    evaluate to a mapping, the contents of which are treated as
    additional keyword
    arguments."<br>
    <br>
    That's fine, but what is a keyword argument?&nbsp; According to the
    glossary (<a class="moz-txt-link-freetext" href="http://docs.python.org/3.3/glossary.html">http://docs.python.org/3.3/glossary.html</a>):<br>
    <br>
    <em class="dfn">"keyword argument</em>: an argument preceded by an
    identifier (e.g.
    <tt class="docutils literal"><span class="pre">name=</span></tt>) in
    a function call or passed as a value in a dictionary
    preceded by <tt class="docutils literal"><span class="pre">**</span></tt>."<br>
    <br>
    As far as I'm concerned, this leads to some ambiguity in whether the
    keys of the mapping need to be valid identifiers or not.<br>
    <br>
    Using Cpython, we can do the following:<br>
    <br>
    &nbsp;&nbsp;&nbsp;&nbsp; def func(**kwargs):<br>
    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; print kwargs<br>
    <br>
    &nbsp; &nbsp;&nbsp; d = {'foo bar baz':3}<br>
    <br>
    So that might lead us to believe that the keys of the mapping do not
    need to be valid identifiers.&nbsp; However, the previous function does
    not work with the following dictionary:<br>
    <br>
    &nbsp;&nbsp;&nbsp; d = {1:3}<br>
    <br>
    because not all the keys are strings.&nbsp; Is there a way to petition to
    get this more rigorously defined?<br>
    <br>
    Thanks,<br>
    ~Matt<br>
    <br>
    <br>
    <br>
  </body>
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