How Python calculate number?
<blockquote>
  <p><strong>Possible Duplicate:</strong><br />
  <a href="http://stackoverflow.com/questions/286061/python-decimal-place-issues-with-floats">python - decimal place issues with floats</a>  </p>
</blockquote>

<p>In [4]: 52+121.2 </p>

<p>Out[4]: 173.19999999999999 </p>
