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75 lines
4.5 KiB
75 lines
4.5 KiB
<!DOCTYPE doctype PUBLIC "-//w3c//dtd html 4.0 transitional//en">
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<html><head>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<meta name="GENERATOR" content="Mozilla/4.51 (Macintosh; I; PPC) [Netscape]"><title>FAQ.html</title></head>
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<body>
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<center> <h1> <hr width="100%">Pyrex FAQ
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<hr width="100%"></h1>
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</center>
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<h2> Contents</h2>
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<ul>
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<li> <b><a href="#CallCAPI">How do I call Python/C API routines?</a></b></li>
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<li> <b><a href="#NullBytes">How do I convert a C string containing null
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bytes to a Python string?</a></b></li>
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<li> <b><a href="#NumericAccess">How do I access the data inside a Numeric
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array object?</a></b></li>
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<li><b><a href="#Rhubarb">Pyrex says my extension type object has no attribute
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'rhubarb', but I know it does. What gives?</a></b></li><li><a style="font-weight: bold;" href="#Quack">Python says my extension type has no method called 'quack', but I know it does. What gives?</a><br>
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</li>
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</ul>
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<hr width="100%"> <h2> <a name="CallCAPI"></a>How do I call Python/C API routines?</h2>
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Declare them as C functions inside a <tt>cdef extern from</tt> block.
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Use the type name <tt>object</tt> for any parameters and return types which
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are Python object references. Don't use the word <tt>const</tt> anywhere.
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Here is an example which defines and uses the <tt>PyString_FromStringAndSize</tt> routine:
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<blockquote><tt>cdef extern from "Python.h":</tt> <br>
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<tt> object PyString_FromStringAndSize(char *, int)</tt> <p><tt>cdef char buf[42]</tt> <br>
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<tt>my_string = PyString_FromStringAndSize(buf, 42)</tt></p>
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</blockquote>
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<h2> <a name="NullBytes"></a>How do I convert a C string containing null
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bytes to a Python string?</h2>
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Put in a declaration for the <tt>PyString_FromStringAndSize</tt> API routine
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and use that<tt>.</tt> See <a href="#CallCAPI">How do I call Python/C API
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routines?</a> <h2> <a name="NumericAccess"></a>How do I access the data inside a Numeric
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array object?</h2>
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Use a <tt>cdef extern from</tt> block to include the Numeric header file
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and declare the array object as an external extension type. The following
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code illustrates how to do this:
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<blockquote><tt>cdef extern from "Numeric/arrayobject.h":</tt> <p><tt> struct PyArray_Descr:</tt> <br>
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<tt> int type_num, elsize</tt> <br>
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<tt> char type</tt> </p>
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<p><tt> ctypedef class Numeric.ArrayType [object PyArrayObject]</tt><tt>:</tt> <br>
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<tt> cdef char *data</tt> <br>
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<tt> cdef int nd</tt> <br>
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<tt> cdef int *dimensions,
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*strides</tt> <br>
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<tt> cdef object base</tt>
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<br>
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<tt> cdef PyArray_Descr *descr</tt> <br>
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<tt> cdef int flags<br>
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</tt></p>
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</blockquote>
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<p>For more information about external extension types, see the <a href="extension_types.html#ExternalExtTypes">"External Extension Types"</a>
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section of the <a href="extension_types.html">"Extension Types"</a> documentation
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page.<br>
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<tt> </tt> </p>
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<h2><a name="Rhubarb"></a>Pyrex says my extension type object has no attribute
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'rhubarb', but I know it does. What gives?</h2>
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You're probably trying to access it through a reference which Pyrex thinks
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is a generic Python object. You need to tell Pyrex that it's a reference
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to your extension type by means of a declaration. For example,<br>
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<blockquote><tt>cdef class Vegetables:</tt><br>
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<tt> cdef int rhubarb</tt><br>
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<br>
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<tt>...</tt><br>
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<tt>cdef Vegetables veg</tt><br>
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<tt>veg.rhubarb = 42</tt><br>
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</blockquote>
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Also see the <a href="Manual/extension_types.html#ExtTypeAttrs">"Attributes"</a>
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section of the <a href="Manual/extension_types.html">"Extension
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Types"</a> documentation page.<br>
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<h2><a name="Quack"></a>Python says my extension type has no method called 'quack', but I know it does. What gives?</h2>
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You may have declared the method using <span style="font-family: monospace;">cdef</span> instead of <span style="font-family: monospace;">def</span>. Only functions and methods declared with <span style="font-family: monospace;">def</span> are callable from Python code.<br><br>
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---
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</body></html> |