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POHow to distinguish different types of NaN float in Python
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  1. POHow to distinguish different types of NaN float in Python
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    copied!<p>I'm writing Python 2.6 code that interfaces with <a href="http://www.ni.com/teststand/" rel="noreferrer">NI TestStand</a> 4.2 via COM in Windows. I want to make a "NAN" value for a variable, but if I pass it <code>float('nan')</code>, TestStand displays it as <code>IND</code>.</p> <p>Apparently TestStand distinguishes between floating point "IND" and "NAN" values. According to <a href="http://zone.ni.com/reference/en-XX/help/370052H-01/tssuppref/infotopics/special_constant_values/" rel="noreferrer">TestStand help</a>:</p> <ul> <li><code>IND</code> corresponds to <em>Signaling NaN</em> in Visual C++, while</li> <li><code>NAN</code> corresponds to <em>QuietNaN</em></li> </ul> <p>That implies that Python's <code>float('nan')</code> is effectively a <em>Signaling NaN</em> when passed through COM. However, from what I've read about <em>Signaling NaN</em>, it seems that <em>Signaling NaN</em> is a bit "exotic" and <em>Quiet NaN</em> is your "regular" NaN. So I have my doubts that Python would be passing a <em>Signaling NaN</em> through COM. <strong>How could I find out if a Python <code>float('nan')</code> is passed through COM as a <em>Signaling NaN</em> or <em>Quiet NaN</em>, or maybe <em>Indeterminate</em>?</strong></p> <p>Is there any way to make a <em>Signaling NaN</em> versus <em>QuietNaN</em> or <em>Indeterminate</em> in Python, when interfacing with other languages? (Using <code>ctypes</code> perhaps?) I assume this would be a platform-specific solution, and I'd accept that in this case.</p> <p><strong>Update:</strong> In the TestStand sequence editor, I tried making two variables, one set to <code>NAN</code> and the other set to <code>IND</code>. Then I saved it to a file. Then I opened the file and read each variable using Python. In both cases, Python reads them as a <code>nan</code> float.</p>
 

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