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copied!<p>If you are worried about b or c being functions that are called instead of just variables that are evaluated, then this code shows that short-circuiting is your friend:</p> <pre><code>a = False def b(): print "b was called" return True if a and b(): print "this shouldn't happen" else: print "if b was not called, then short-circuiting works" </code></pre> <p>prints</p> <pre><code>if b was not called, then short-circuiting works </code></pre> <p>But if you have code that does this:</p> <pre><code>a = call_to_expensive_function_A() b = call_to_expensive_function_B() c = call_to_expensive_function_C() if a and b and c: do something... </code></pre> <p>then your code is still calling all 3 expensive functions. Better to let Python be Python:</p> <pre><code>if (call_to_expensive_function_A() and call_to_expensive_function_B() and call_to_expensive_function_C()) do something... </code></pre> <p>which will only call as many expensive functions as necessary to determine the overall condition.</p> <p><strong>Edit</strong></p> <p>You can generalize this using the <code>all</code> built-in:</p> <pre><code># note, this is a list of the functions themselves # the functions are *not* called when creating this list funcs = [function_A, function_B, function_C] if all(fn() for fn in funcs): do something </code></pre> <p>Now if you have to add other functions, or want to reorder them (maybe <code>function_A</code> is very time-consuming, and you would benefit by filtering cases that fail <code>function_B</code> or <code>function_C</code> first), you just update the <code>funcs</code> list. <code>all</code> does short-circuiting just as if you had spelled out the if as <code>if a and b and c</code>. (If functions are 'or'ed together, use <code>any</code> builtin instead.)</p>

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