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    <p>Yeah, as Evan said, don't type check. Just try to use the value:</p> <pre><code>def myintfunction(value): """ Please pass an integer """ return 2 + value </code></pre> <p>That doesn't have a typecheck. It is much better! Let's see what happens when I try it:</p> <pre><code>&gt;&gt;&gt; myintfunction(5) 7 </code></pre> <p>That works, because it is an integer. Hm. Lets try some text.</p> <pre><code>&gt;&gt;&gt; myintfunction('text') Traceback (most recent call last): File "&lt;stdin&gt;", line 1, in &lt;module&gt; File "&lt;stdin&gt;", line 3, in myintfunction TypeError: unsupported operand type(s) for +: 'int' and 'str' </code></pre> <p>It shows an error, TypeError, which is what it should do anyway. If caller wants to catch that, it is possible. </p> <p>What would you do if you did a typecheck? Show an error right? So you don't have to typecheck because the error is already showing up automatically.</p> <p>Plus since you didn't typecheck, you have your function working with other types:</p> <p>Floats:</p> <pre><code>&gt;&gt;&gt; print myintfunction(2.2) 4.2 </code></pre> <p>Complex numbers:</p> <pre><code>&gt;&gt;&gt; print myintfunction(5j) (2+5j) </code></pre> <p>Decimals:</p> <pre><code>&gt;&gt;&gt; import decimal &gt;&gt;&gt; myintfunction(decimal.Decimal('15')) Decimal("17") </code></pre> <p>Even completely arbitrary objects that can add numbers!</p> <pre><code>&gt;&gt;&gt; class MyAdderClass(object): ... def __radd__(self, value): ... print 'got some value: ', value ... return 25 ... &gt;&gt;&gt; m = MyAdderClass() &gt;&gt;&gt; print myintfunction(m) got some value: 2 25 </code></pre> <p>So you clearly get nothing by typechecking. And lose a lot.</p> <hr> <h1>UPDATE:</h1> <p>Since you've edited the question, it is now clear that your application calls some upstream routine that makes sense only with ints. </p> <p>That being the case, I still think you should pass the parameter <strong>as received</strong> to the upstream function. The upstream function will deal with it correctly e.g. raising an error if it needs to. I highly <strong>doubt that</strong> your function that deals with IPs will behave strangely if you pass it a float. If you can give us the name of the library we can check that for you.</p> <p>But... If the upstream function will behave incorrectly and kill some kids if you pass it a float (I still highly doubt it), then just just call <code>int()</code> on it:</p> <pre><code>def myintfunction(value): """ Please pass an integer """ return upstreamfunction(int(value)) </code></pre> <p>You're still not typechecking, so you get most benefits of not typechecking.</p> <hr> <p>If even after all that, you really want to type check, despite it reducing your application's readability and performance for absolutely no benefit, use an <code>assert</code> to do it.</p> <pre><code>assert isinstance(...) assert type() is xxxx </code></pre> <p>That way we can turn off <code>assert</code>s and remove this <code>&lt;sarcasm&gt;</code><em>feature</em><code>&lt;/sarcasm&gt;</code> from the program by calling it as</p> <pre><code>python -OO program.py </code></pre>
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    1. POHow can I type-check variables in Python?
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    1. COHe said that the function won't work if the argument isn't an int. Having the function "work" with floats and complex numbers because it isn't typechecked is a bug, not a feature
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    2. CO@Nick: If it won't work if the argument isn't a int, what would it do instead? Raise error? Well, python does that already. Also, if the func works with other types like float then that isn't a bug, it's a feature, because the func is *working*. Making it not work would be an artificial restriction.
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    3. CO@Nick: How can you *know* that the function won't work without an int? What if I provide an object that is not an int but behaves exactly as an int? Why that shouldn't work?
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