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    <p>Its a matter of <a href="http://docs.python.org/2/reference/expressions.html#operator-precedence" rel="nofollow">operator precedence</a>.</p> <p>In the case of your expressions, the implicit ordering is as follows</p> <pre><code>((len(str) &lt; 2) and str) or ('doh ' + str + ' /doh') </code></pre> <p>In the case of <code>str = ""</code>, <code>len(str) &lt; 2</code> evaluates <code>True</code>, but <code>str</code>, an empty string, evaluates to <code>False</code>, thus the <code>and</code> expression is <code>False</code>, so the right operand of the <code>or</code> binary op becomes the result of the expression.</p> <p>For the case of <code>str = "abc"</code>, <code>len(str) &lt; 2</code> is <code>False</code>, so the <code>and</code> expression short-circuits as <code>False</code>, and the expression to the right of the <code>or</code> is the result.</p> <p>For the case of <code>str = "ab"</code>, <code>len(str) &lt; 2</code> is True, so the <code>and</code> expression passes its right operand to the <code>or</code> binary operator, and since <code>bool("ab") == True</code>, the value of <code>str</code> becomes the result of the expression.</p> <p>As you can see, using <code>and</code>/<code>or</code> will not work similarly to other language's ternary operators if your result in the case of a <code>True</code> condition is equivalent to <code>False</code>, e.g. <code>True and 0 or 1</code> yields <code>1</code>, whereas using <code>0 if True else 1</code> yields <code>0</code>.</p> <p>I'd recommend using python's ternary if/else expression, e.g.:</p> <pre><code>str if len(str) &lt; 2 else 'doh ' + str + ' /doh' </code></pre>
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    1. COSorry, nope that's not it; this isn't a logical and/or; this is a ternary statement. I'll explain in my answer... Toclarify, I was omitting the return because I ran this statement directly into IDLE by typing "str = ''"<return>"len(str) < 2 and str or 'doh ' + str + ' /doh'"
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    2. COPrior to python 2.6, python didn't support ternary operators, but because of the low binding + short-circuiting of logical and/or operators, you can use them to simulate a ternary operator as you describe, but `x and y or z` will not work if `bool(y) == False`. In python 2.6+, use the `y if x else z` ternary expression instead.
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    3. COI apologise, you're absolutely right; I was mistaking the form for a ternary operator to something else entirely; def f_b(str): str if len(str)<2 else str[-1]+str[1:-1]+str[0] works perfectly.
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