devn00b
/
EQ2EMu


			
							123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132
							

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
  "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
  <head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
    
    <title>How to use dtypes - Boost.Python NumPy extension 1.0 documentation</title>
    <link rel="stylesheet" href="../_static/pygments.css" type="text/css" />
    <link rel="stylesheet" href="../_static/style.css" type="text/css" />
    <script type="text/javascript">
      var DOCUMENTATION_OPTIONS = {
          URL_ROOT:    '../',
          VERSION:     '1.0',
          COLLAPSE_MODINDEX: false,
          FILE_SUFFIX: '.html'
      };
    </script>
    <script type="text/javascript" src="../_static/jquery.js"></script>
    <script type="text/javascript" src="../_static/underscore.js"></script>
    <script type="text/javascript" src="../_static/doctools.js"></script>
    <link rel="index" title="Index" href="../genindex.html" />
    <link rel="search" title="Search" href="../search.html" />
    <link rel="top" title="Boost.Python NumPy extension 1.0 documentation" href="../index.html" />
    <link rel="up" title="Boost.Python NumPy extension Tutorial" href="index.html" />
    <link rel="next" title="Creating ndarrays" href="ndarray.html" />
    <link rel="prev" title="A simple tutorial on Arrays" href="simple.html" /> 
  </head>
  <body>
    <div class="header">
    <table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
    "header">
      <tr>
        <td valign="top" width="300">
          <h3><a href="../index.html"><img 
          alt="C++ Boost" src="../_static/bpl.png" border="0"></a></h3>
        </td>

        <td >
          <h1 align="center"><a href="../index.html">(NumPy)</a></h1>
<!--          <h2 align="center">CallPolicies Concept</h2>-->
        </td>
	<td>
      <div id="searchbox" style="display: none">
        <form class="search" action="../search.html" method="get">
          <input type="text" name="q" size="18" />
          <input type="submit" value="Search" />
          <input type="hidden" name="check_keywords" value="yes" />
          <input type="hidden" name="area" value="default" />
        </form>
      </div>
      <script type="text/javascript">$('#searchbox').show(0);</script>
	</td>
      </tr>
    </table>
    </div>
    <hr/>
    <div class="content">
    <div class="navbar" style="text-align:right;">
      
      
      <a class="prev" title="A simple tutorial on Arrays" href="simple.html"><img src="../_static/prev.png" alt="prev"/></a>
      <a class="up" title="Boost.Python NumPy extension Tutorial" href="index.html"><img src="../_static/up.png" alt="up"/></a>
      <a class="next" title="Creating ndarrays" href="ndarray.html"><img src="../_static/next.png" alt="next"/></a>
      
    </div>
      
  <div class="section" id="how-to-use-dtypes">
<h1>How to use dtypes</h1>
<p>Here is a brief tutorial to show how to create ndarrays with built-in python data types, and extract the types and values of member variables</p>
<p>Like before, first get the necessary headers, setup the namespaces and initialize the Python runtime and numpy module:</p>
<div class="highlight-c++"><div class="highlight"><pre><span class="cp">#include</span> <span class="cpf">&lt;boost/python/numpy.hpp&gt;</span><span class="cp"></span>
<span class="cp">#include</span> <span class="cpf">&lt;iostream&gt;</span><span class="cp"></span>

<span class="k">namespace</span> <span class="n">p</span> <span class="o">=</span> <span class="n">boost</span><span class="o">::</span><span class="n">python</span><span class="p">;</span>
<span class="k">namespace</span> <span class="n">np</span> <span class="o">=</span> <span class="n">boost</span><span class="o">::</span><span class="n">python</span><span class="o">::</span><span class="n">numpy</span><span class="p">;</span>

<span class="kt">int</span> <span class="nf">main</span><span class="p">(</span><span class="kt">int</span> <span class="n">argc</span><span class="p">,</span> <span class="kt">char</span> <span class="o">**</span><span class="n">argv</span><span class="p">)</span>
<span class="p">{</span>
  <span class="n">Py_Initialize</span><span class="p">();</span>
  <span class="n">np</span><span class="o">::</span><span class="n">initialize</span><span class="p">();</span>
</pre></div>
</div>
<p>Next, we create the shape and dtype. We use the get_builtin method to get the numpy dtype corresponding to the builtin C++ dtype
Here, we will create a 3x3 array passing a tuple with (3,3) for the size, and double as the data type</p>
<div class="highlight-c++"><div class="highlight"><pre><span class="n">p</span><span class="o">::</span><span class="n">tuple</span> <span class="n">shape</span> <span class="o">=</span> <span class="n">p</span><span class="o">::</span><span class="n">make_tuple</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="mi">3</span><span class="p">);</span>
<span class="n">np</span><span class="o">::</span><span class="n">dtype</span> <span class="n">dtype</span> <span class="o">=</span> <span class="n">np</span><span class="o">::</span><span class="n">dtype</span><span class="o">::</span><span class="n">get_builtin</span><span class="o">&lt;</span><span class="kt">double</span><span class="o">&gt;</span><span class="p">();</span>
<span class="n">np</span><span class="o">::</span><span class="n">ndarray</span> <span class="n">a</span> <span class="o">=</span> <span class="n">np</span><span class="o">::</span><span class="n">zeros</span><span class="p">(</span><span class="n">shape</span><span class="p">,</span> <span class="n">dtype</span><span class="p">);</span>
</pre></div>
</div>
<p>Finally, we can print the array using the extract method in the python namespace.
Here, we first convert the variable into a string, and then extract it as a C++ character array from the python string using the &lt;char const * &gt; template</p>
<div class="highlight-c++"><div class="highlight"><pre><span class="n">std</span><span class="o">::</span><span class="n">cout</span> <span class="o">&lt;&lt;</span> <span class="s">&quot;Original array:</span><span class="se">\n</span><span class="s">&quot;</span> <span class="o">&lt;&lt;</span> <span class="n">p</span><span class="o">::</span><span class="n">extract</span><span class="o">&lt;</span><span class="kt">char</span> <span class="k">const</span> <span class="o">*&gt;</span><span class="p">(</span><span class="n">p</span><span class="o">::</span><span class="n">str</span><span class="p">(</span><span class="n">a</span><span class="p">))</span> <span class="o">&lt;&lt;</span> <span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span>
</pre></div>
</div>
<p>We can also print the dtypes of the data members of the ndarray by using the get_dtype method for the ndarray</p>
<div class="highlight-c++"><div class="highlight"><pre><span class="n">std</span><span class="o">::</span><span class="n">cout</span> <span class="o">&lt;&lt;</span> <span class="s">&quot;Datatype is:</span><span class="se">\n</span><span class="s">&quot;</span> <span class="o">&lt;&lt;</span> <span class="n">p</span><span class="o">::</span><span class="n">extract</span><span class="o">&lt;</span><span class="kt">char</span> <span class="k">const</span> <span class="o">*&gt;</span><span class="p">(</span><span class="n">p</span><span class="o">::</span><span class="n">str</span><span class="p">(</span><span class="n">a</span><span class="p">.</span><span class="n">get_dtype</span><span class="p">()))</span> <span class="o">&lt;&lt;</span> <span class="n">std</span><span class="o">::</span><span class="n">endl</span> <span class="p">;</span>
</pre></div>
</div>
<p>We can also create custom dtypes and build ndarrays with the custom dtypes</p>
<p>We use the dtype constructor to create a custom dtype. This constructor takes a list as an argument.</p>
<p>The list should contain one or more tuples of the format (variable name, variable type)</p>
<p>So first create a tuple with a variable name and its dtype, double, to create a custom dtype</p>
<div class="highlight-c++"><div class="highlight"><pre><span class="n">p</span><span class="o">::</span><span class="n">tuple</span> <span class="n">for_custom_dtype</span> <span class="o">=</span> <span class="n">p</span><span class="o">::</span><span class="n">make_tuple</span><span class="p">(</span><span class="s">&quot;ha&quot;</span><span class="p">,</span><span class="n">dtype</span><span class="p">)</span> <span class="p">;</span>
</pre></div>
</div>
<p>Next, create a list, and add this tuple to the list. Then use the list to create the custom dtype</p>
<div class="highlight-c++"><div class="highlight"><pre><span class="n">p</span><span class="o">::</span><span class="n">list</span> <span class="n">list_for_dtype</span> <span class="p">;</span>
<span class="n">list_for_dtype</span><span class="p">.</span><span class="n">append</span><span class="p">(</span><span class="n">for_custom_dtype</span><span class="p">)</span> <span class="p">;</span>
<span class="n">np</span><span class="o">::</span><span class="n">dtype</span> <span class="n">custom_dtype</span> <span class="o">=</span> <span class="n">np</span><span class="o">::</span><span class="n">dtype</span><span class="p">(</span><span class="n">list_for_dtype</span><span class="p">)</span> <span class="p">;</span>
</pre></div>
</div>
<p>We are now ready to create an ndarray with dimensions specified by *shape* and of custom dtpye</p>
<div class="highlight-c++"><div class="highlight"><pre>  <span class="n">np</span><span class="o">::</span><span class="n">ndarray</span> <span class="n">new_array</span> <span class="o">=</span> <span class="n">np</span><span class="o">::</span><span class="n">zeros</span><span class="p">(</span><span class="n">shape</span><span class="p">,</span><span class="n">custom_dtype</span><span class="p">);</span>
<span class="p">}</span>
</pre></div>
</div>
</div>


    <div class="navbar" style="text-align:right;">
      
      
      <a class="prev" title="A simple tutorial on Arrays" href="simple.html"><img src="../_static/prev.png" alt="prev"/></a>
      <a class="up" title="Boost.Python NumPy extension Tutorial" href="index.html"><img src="../_static/up.png" alt="up"/></a>
      <a class="next" title="Creating ndarrays" href="ndarray.html"><img src="../_static/next.png" alt="next"/></a>
      
    </div>
    </div>
  </body>
</html>