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copied!<p>so <a href="http://www.python.org/dev/peps/pep-3113/" rel="nofollow">pep 3113</a>, as artur gaspar points out, contains a full answer. It also lists a whole bunch of reasons why this probably isn't a great pattern to follow. One of these you discovered in the annoying side effects of debugging. A bigger one is I think that your code will break transitioning to python3, but I'm not sure/still am on 2.7 personally.</p> <p>I wanted to play with what happens. Looking as some disassembled bytecodes we can see what happens with these three functions (spoiler: foo and bar have identical bytecodes):</p> <pre><code>from dis import dis def foo(a, (b, c) ,d): return a + b + c + d def bar(a, b_c, d): b, c = b_c return a + b + c + d def baz(a, b, c, d): return a + b + c + d print '\nfoo:' dis(foo) print '\nbar:' dis(bar) print '\nbaz:' dis(baz) </code></pre> <p>Yields:</p> <pre><code>foo: 3 0 LOAD_FAST 1 (.1) 3 UNPACK_SEQUENCE 2 6 STORE_FAST 3 (b) 9 STORE_FAST 4 (c) 4 12 LOAD_FAST 0 (a) 15 LOAD_FAST 3 (b) 18 BINARY_ADD 19 LOAD_FAST 4 (c) 22 BINARY_ADD 23 LOAD_FAST 2 (d) 26 BINARY_ADD 27 RETURN_VALUE bar: 7 0 LOAD_FAST 1 (b_c) 3 UNPACK_SEQUENCE 2 6 STORE_FAST 3 (b) 9 STORE_FAST 4 (c) 8 12 LOAD_FAST 0 (a) 15 LOAD_FAST 3 (b) 18 BINARY_ADD 19 LOAD_FAST 4 (c) 22 BINARY_ADD 23 LOAD_FAST 2 (d) 26 BINARY_ADD 27 RETURN_VALUE baz: 11 0 LOAD_FAST 0 (a) 3 LOAD_FAST 1 (b) 6 BINARY_ADD 7 LOAD_FAST 2 (c) 10 BINARY_ADD 11 LOAD_FAST 3 (d) 14 BINARY_ADD 15 RETURN_VALUE </code></pre> <p>As you can see. <code>foo</code> and <code>bar</code> are identical, while <code>baz</code> skips the unpacking. So yes, this will affect performance a bit, but only as long as tuple unpacking takes, which should be negligible in everything except very small functions and toy examples (like this one ;P)</p>

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