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copied!<p>A <b>lambda</b> is just an anonymous function - a function defined with no name. In some languages, such as Scheme, they are equivalent to named functions. In fact, the function definition is re-written as binding a lambda to a variable internally. In other languages, like Python, there are some (rather needless) distinctions between them, but they behave the same way otherwise.</p> <p>A <b>closure</b> is any function which <b>closes over</b> the <b>environment</b> in which it was defined. This means that it can access variables not in its parameter list. Examples:</p> <pre><code>def func(): return h def anotherfunc(h): return func() </code></pre> <p>This will cause an error, because <code>func</code> does not <b>close over</b> the environment in <code>anotherfunc</code> - <code>h</code> is undefined. <code>func</code> only closes over the global environment. This will work:</p> <pre><code>def anotherfunc(h): def func(): return h return func() </code></pre> <p>Because here, <code>func</code> is defined in <code>anotherfunc</code>, and in python 2.3 and greater (or some number like this) when they <i>almost</i> got closures correct (mutation still doesn't work), this means that it <b>closes over</b> <code>anotherfunc</code>'s environment and can access variables inside of it. In Python 3.1+, mutation works too when using <a href="http://docs.python.org/release/3.1.3/reference/simple_stmts.html#nonlocal" rel="noreferrer">the <code>nonlocal</code> keyword</a>.</p> <p>Another important point - <code>func</code> will continue to close over <code>anotherfunc</code>'s environment even when it's no longer being evaluated in <code>anotherfunc</code>. This code will also work:</p> <pre><code>def anotherfunc(h): def func(): return h return func print anotherfunc(10)() </code></pre> <p>This will print 10.</p> <p>This, as you notice, has nothing to do with <b>lambda</b>s - they are two different (although related) concepts.</p>

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