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copied!<p><code>lambda</code> clearly is a keyword; it's a special word recognised by the parser, which would otherwise fall within the definition of an <code>identifier</code>.</p> <p><code>lambda</code> is not <em>semantically</em> an operator. An operator is just a function, but invoked with a different syntax. We can imagine replacing the <code>+</code> operator with an <code>add</code> function; all our programs with addition would get more verbose and harder to read, but we could still write them. The <code>lambda</code> language construct on the other hand could not be replaced with a function; <code>lambda x: x+1</code> is not just calculating a result from the values <code>x</code> and <code>x+1</code>, because in this context they are not values at all (<code>x</code> is the name of the parameter to the function being defined, and <code>x+1</code> is the code of the lambda body).</p> <p>In the same page you linked to we have: <a href="http://docs.python.org/py3k/reference/lexical_analysis.html#operators" rel="nofollow">http://docs.python.org/py3k/reference/lexical_analysis.html#operators</a></p> <blockquote> <p>The following tokens are operators:</p> <pre><code>+ - * ** / // % << >> & | ^ ~ < > <= >= == != </code></pre> </blockquote> <p>That's the entire contents of the subsection on operators. From this I take it to mean that in the context of defining the tokens of the language "operators" are symbolic operators, whereas the section on <em>keywords</em> is explicitly spelling out that "these things which would otherwise be identifiers are keywords". That's why I think the keyword operators like <code>not</code>, <code>is</code>, <code>in</code>, etc are not listed. But there certainly are things that are semantically operators that are keywords, whether or not the parser considers them separate classes.</p> <p>I'm not sure why <a href="http://docs.python.org/py3k/reference/expressions.html#summary" rel="nofollow">http://docs.python.org/py3k/reference/expressions.html#summary</a> describes <code>lambda</code> as an operator; I certainly wouldn't. Strictly speaking it doesn't explicitly say "<code>lambda</code> is the operator with the lowest precedence", it just lists <code>lambda</code> in a table whose column heading is "Operator". Perhaps it was just a convenience; describing <code>lambda</code> as a thing with low precedence is a good way of clarifying how Python will parse <code>lambda x: x + 1</code> (it could theoretically be either <code>(lambda x: x) + 1</code> or <code>lambda x: (x + 1)</code>).</p>

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