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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html><head>
<meta content="text/html; charset=ISO-8859-1" http-equiv="content-type"><title>Language Basics</title>
</head>
<body>
<h1>
<hr style="width: 100%; height: 2px;">Language
Basics
<hr width="100%"></h1>
<ul id="mozToc">
<!--mozToc h2 1 h3 2--><li><a href="#mozTocId641350">Python
functions vs. C functions</a></li>
<li><a href="#mozTocId972536">Python objects as
parameters
and return values</a></li>
<li><a href="#mozTocId155104">C
variable and type definitions</a>
<ul>
<li><a href="#mozTocId890190">Forward
Declarations</a></li>
<li><a href="#mozTocId522210">Grouping
multiple C declarations</a></li>
</ul>
</li>
<li><a href="#mozTocId763321">Automatic
type conversions</a>
<ul>
<li><a href="#mozTocId440941">Caveats
when using a Python string in a C context</a></li>
</ul>
</li>
<li><a href="#mozTocId834148">Scope rules</a></li>
<li><a href="#mozTocId954330">Statements and
expressions</a>
<ul>
<li><a href="#mozTocId401576">Differences
between C
and Pyrex
expressions</a></li>
<li><a href="#mozTocId899067">Integer for-loops</a></li>
<li><a href="#mozTocId457396">Catching
exceptions and tracebacks</a></li>
</ul>
</li>
<li><a href="#mozTocId482761">Error return values</a>
<ul>
<li><a href="#mozTocId622828">Checking
return values of non-Pyrex functions</a></li>
</ul>
</li>
<li><a href="#mozTocId494354">The include
statement</a></li>
<li><a href="#mozTocId849661">Keyword-only
arguments</a></li>
<li><a href="#mozTocId829237">Built-in Names</a>
<ul>
<li><a href="#mozTocId813519">Built-in
Constants</a></li>
<li><a href="#mozTocId593628">Built-in
Functions</a></li>
<li><a href="#mozTocId452377">Built-in Types</a></li>
</ul>
</li>
<li><a href="#mozTocId42018">Conditional
Compilation</a>
<ul>
<li><a href="#mozTocId379306">Compile-Time
Definitions</a></li>
<li><a href="#mozTocId997015">Conditional
Statements</a></li>
</ul>
</li>
</ul>
This
section describes the basic features of the Pyrex language. The
facilities covered in this section allow you to create Python-callable
functions that manipulate C data structures and convert between Python
and C data types. Later sections will cover facilities for <a href="external.html">wrapping external C code</a>, <a href="extension_types.html">creating new Python types</a>
and <a href="sharing.html">cooperation between Pyrex
modules</a>.<br>
<h2><a class="mozTocH2" name="mozTocId641350"></a>
<a name="PyFuncsVsCFuncs"></a>Python
functions vs. C functions</h2>
There are two kinds of function
definition in Pyrex:
<p><b>Python functions</b> are
defined using the <b>def</b> statement, as in Python. They
take Python objects as parameters and return Python objects. </p>
<p><b>C functions</b> are defined using the new <b>cdef</b>
statement. They take either Python objects or C values as parameters,
and can return either Python objects or C values. </p>
<p>Within
a Pyrex module, Python functions and C functions can call each other
freely, but only Python functions can be called from outside the module
by
interpreted Python code. So, any functions that you want to "export"
from your Pyrex module must be declared as Python functions using <span style="font-weight: bold;">def</span>. </p>
<p>Parameters
of either type of function can be declared to have C data types, using
normal C declaration syntax. For example, </p>
<blockquote>
<pre>def spam(int i, char *s):<br> ...</pre>
<pre>cdef int eggs(unsigned long l, float f):<br> ...</pre>
</blockquote>
When
a parameter of a Python function is declared
to have a C data type, it is passed in as a Python object and
automatically converted to a C value, if possible. Automatic conversion
is currently only possible for numeric types and string types;
attempting to use any other type for the parameter of a Python function
will result in a compile-time error.
<p>C functions, on the
other hand, can have parameters of any type, since they're passed in
directly using a normal C function call. </p>
<h2><a class="mozTocH2" name="mozTocId972536"></a>
<a name="PyObjParams"></a>Python objects as
parameters
and return values</h2>
If no type is specified for a parameter or
return value, <i>it is assumed to be a Python object.</i>
(Note that this is different from the C convention, where it would
default to <tt>int</tt>.) For example, the following
defines a C function that takes two Python objects as parameters and
returns a Python object:
<blockquote>
<pre>cdef spamobjs(x, y):<br> ...</pre>
</blockquote>
Reference counting for these objects is performed
automatically according to the standard Python/C API rules (i.e.
borrowed references are taken as parameters and a new reference is
returned).
<p>The name <b>object</b> can also be
used to explicitly declare something as a Python object. This can be
useful if the name being declared would otherwise
be taken as the name of a type, for example, </p>
<blockquote>
<pre>cdef ftang(object int):<br> ...</pre>
</blockquote>
declares
a parameter called <tt>int</tt>
which is a Python object. You can also use <b>object </b>as
the explicit return type of a function, e.g.
<blockquote>
<pre>cdef object ftang(object int):<br> ...</pre>
</blockquote>
In the interests of clarity, it is probably a good
idea to always be explicit about <b>object </b>parameters
in C functions.
<h2><a class="mozTocH2" name="mozTocId155104"></a><a name="CVarAndTypeDecls"></a>C
variable and type definitions</h2>
The <b>cdef</b>
statement is also used to declare C variables, either
local or module-level:
<blockquote>
<pre>cdef int i, j, k<br>cdef float f, g[42], *h</pre>
</blockquote>
and C struct, union or enum types:
<blockquote>
<pre>cdef struct Grail:<br> int age<br> float volume</pre>
<pre>cdef union Food:<br> char *spam<br> float *eggs</pre>
<pre>cdef enum CheeseType:<br> cheddar, edam, <br> camembert</pre>
<pre>cdef enum CheeseState:<br> hard = 1<br> soft = 2<br> runny = 3</pre>
</blockquote>
There is currently no special syntax for defining a
constant, but you
can use an anonymous enum declaration for this purpose, for example,
<blockquote><tt>cdef
enum:</tt> <br>
<tt>
tons_of_spam = 3</tt></blockquote>
Note that the words <span style="font-family: monospace;">struct</span>,
<span style="font-family: monospace;">union</span>
and <span style="font-family: monospace;">enum</span>
are used
only when <i>defining</i> a type, not when referring to
it. For example, to declare a variable pointing to a Grail you would
write
<blockquote>
<pre>cdef Grail *gp</pre>
</blockquote>
and <i>not</i>
<blockquote>
<pre>cdef struct Grail *gp <font color="#ed181e"># WRONG</font></pre>
</blockquote>
There is also a <b>ctypedef</b> statement for giving names
to types, e.g.
<blockquote>
<pre>ctypedef unsigned long ULong</pre>
<pre>ctypedef int *IntPtr<br></pre>
</blockquote>
<h3><a class="mozTocH2" name="mozTocId890190"></a>Forward
Declarations</h3>
If
you have two struct or union types containing pointers that refer to
each other, you will need to use a forward declaration for at least one
of them. This is simply the header of a struct or union without the
colon or body, for example,<br>
<br>
<div style="margin-left: 40px;"><span style="font-family: monospace;">cdef struct Sandwich</span><br style="font-family: monospace;">
<br style="font-family: monospace;">
<span style="font-family: monospace;">cdef struct Lunchbox:</span><br style="font-family: monospace;">
<div style="margin-left: 40px;"><span style="font-family: monospace;">Sandwich *lunch</span><br style="font-family: monospace;">
</div>
<br style="font-family: monospace;">
<span style="font-family: monospace;">cdef struct Sandwich:</span><br style="font-family: monospace;">
<div style="margin-left: 40px;"><span style="font-family: monospace;">Lunchbox *container</span><br>
</div>
</div>
<br>
You
can also forward-declare C functions, but there should be little need
to do this. Pyrex processes all declarations in a module before
analysing any executable statements, so calling a function defined
further down in the source file is usually not a problem.
<h3><a class="mozTocH2" name="mozTocId522210"></a><a name="Grouping_multiple_C_declarations"></a>Grouping
multiple C declarations</h3>
If you have a series of declarations that all begin with <span style="font-family: monospace;">cdef</span>, you can
group them into a cdef block like this:<br>
<pre style="margin-left: 40px;">cdef:<br><br> struct Spam:<br> int tons<br><br> int i<br> float f<br> Spam *p<br><br> void f(Spam *s):<br> print s.tons, "Tons of spam"<br> </pre>
<h2><a class="mozTocH2" name="mozTocId763321"></a><a name="AutomaticTypeConversions"></a>Automatic
type conversions</h2>
In most situations, automatic conversions will be performed for the
basic numeric and string types when a Python object is used in a
context requiring a C value, or vice versa. The following table
summarises the conversion possibilities.<br>
<br>
<table style="text-align: left; background-color: rgb(204, 255, 255); width: 10%; margin-left: 40px;" border="1" cellpadding="4" cellspacing="0">
<tbody>
<tr>
<th style="vertical-align: top; width: 40%; white-space: nowrap; background-color: rgb(255, 204, 51);">C
types<br>
</th>
<th style="vertical-align: top; width: 150px; white-space: nowrap; background-color: rgb(255, 204, 51);">From
Python types<br>
</th>
<th style="vertical-align: top; width: 150px; white-space: nowrap; background-color: rgb(255, 204, 51);">To
Python types<br>
</th>
</tr>
<tr>
<td colspan="1" rowspan="1" style="vertical-align: top; width: 40%; white-space: nowrap;">[unsigned]
char<br>
[unsigned] short<br>
int, long</td>
<td colspan="1" rowspan="1" style="vertical-align: top; width: 150px; white-space: nowrap;">int,
long<br>
</td>
<td colspan="1" rowspan="1" style="vertical-align: top; width: 150px; white-space: nowrap;">int<br>
</td>
</tr>
<tr>
</tr>
<tr>
<td colspan="1" rowspan="1" style="vertical-align: top; width: 40%; white-space: nowrap;">unsigned
int<br>
unsigned long<br>
[unsigned] long long<br>
</td>
<td colspan="1" rowspan="1" style="vertical-align: top; white-space: nowrap;">int, long<br>
<br>
</td>
<td colspan="1" rowspan="1" style="vertical-align: top; white-space: nowrap;">long<br>
<br>
</td>
</tr>
<tr>
</tr>
<tr>
<td style="vertical-align: top; width: 40%; white-space: nowrap;">float,
double, long double<br>
</td>
<td style="vertical-align: top; width: 150px; white-space: nowrap;">int,
long, float<br>
</td>
<td style="vertical-align: top; width: 150px; white-space: nowrap;">float<br>
</td>
</tr>
<tr>
<td style="vertical-align: top; width: 40%; white-space: nowrap;">char
*<br>
</td>
<td style="vertical-align: top; width: 150px; white-space: nowrap;">str<span style="font-style: italic;"></span><br>
</td>
<td style="vertical-align: top; width: 150px; white-space: nowrap;">str<br>
</td>
</tr>
</tbody>
</table>
<br>
<h3><a class="mozTocH3" name="mozTocId440941"></a><a name="PyToCStringCaveats"></a>Caveats
when using a Python string in a C context</h3>
You need to be careful when using a Python string in a context
expecting a <span style="font-family: monospace;">char *</span>.
In this situation, a pointer to the contents of the Python string is
used, which is only valid as long as the Python string exists. So you
need to make sure that a reference to the original Python string is
held for as long as the C string is needed. If you can't guarantee that
the Python string will live long enough, you will need to copy the C
string.<br>
<br>
Pyrex detects and prevents <span style="font-style: italic;">some</span>
mistakes of
this kind. For instance, if you attempt something like<br>
<pre style="margin-left: 40px;">cdef char *s<br>s = pystring1 + pystring2</pre>
then
Pyrex will produce the error message "<span style="font-weight: bold;">Obtaining char * from temporary
Python value</span>".
The reason is that concatenating the two Python strings produces a new
Python string object that is referenced only by a temporary internal
variable that Pyrex generates. As soon as the statement has finished,
the temporary variable will be decrefed and the Python string
deallocated, leaving <span style="font-family: monospace;">s</span>
dangling. Since this code could not possibly work, Pyrex refuses to
compile it.<br>
<br>
The solution is to assign the result of the concatenation to
a Python variable, and then obtain the char * from that, i.e.<br>
<pre style="margin-left: 40px;">cdef char *s<br>p = pystring1 + pystring2<br>s = p<br></pre>
It
is then your responsibility to hold the reference <span style="font-family: monospace;">p</span> for as long
as necessary.<br>
<br>
Keep in mind that the rules used to detect such errors are
only
heuristics. Sometimes Pyrex will complain unnecessarily, and sometimes
it will fail to detect a problem that exists. Ultimately, you need to
understand the issue and be careful what you do.
<h2><a class="mozTocH2" name="mozTocId834148"></a><a name="ScopeRules"></a>Scope rules</h2>
Pyrex
determines whether a variable belongs to a local scope, the module
scope, or the built-in scope <i>completely statically.</i>
As with Python, assigning to a variable which is not otherwise declared
implicitly declares it to be a Python variable residing in the scope
where it is assigned. Unlike Python, however, a name which is referred
to but not declared or assigned is assumed to reside in the <i>builtin
scope, </i>not the module scope.
Names added to the module dictionary at run time will not shadow such
names.<br>
<br>
This can result in some odd things happening under rare circumstances,
for example<br>
<br>
<div style="margin-left: 40px;"><tt>print __name__</tt></div>
<p>In
Pyrex, instead of printing the name of the current module, this prints
the name of the builtins module. The reason is that because Pyrex
hasn't seen a declaration of anything called <span style="font-family: monospace;">__name__</span> in the
module, it's assumed to reside in the builtins. The solution is to use
a <span style="font-weight: bold;">global</span>
statement to declare <span style="font-family: monospace;">__name__</span>
as a module-level name:</p>
<p style="margin-left: 40px;"><tt>global
__name__</tt><tt><br>
print __name__</tt></p>
Another
consequence of these rules is that the module-level scope behaves the
same way as a Python local scope if you refer to a variable before
assigning to it. In particular, tricks such as the following will <i>not</i>
work
in Pyrex:<br>
<blockquote>
<pre>try:<br> x = True<br>except NameError:<br> True = 1<br></pre>
</blockquote>
because, due to the assignment in the last line, <span style="font-family: monospace;">True</span> will
always be looked up in the module-level scope. You would have to do
something like this instead:<br>
<blockquote>
<pre>import __builtin__<br>try:<br> True = __builtin__.True<br>except AttributeError:<br> True = 1<br></pre>
</blockquote>
<hr width="100%">
<h2><a class="mozTocH2" name="mozTocId954330"></a><a name="StatsAndExprs"></a>Statements and
expressions</h2>
Control structures and expressions follow Python syntax for the most
part. When applied to Python objects, they have the same semantics as
in Python (unless otherwise noted). Most of the Python operators can
also be applied to C values, with the obvious semantics.
<p>If
Python objects and C values are mixed in an expression, conversions are
performed automatically between Python objects and C numeric or string
types. </p>
<p>Reference counts are maintained
automatically for all Python objects, and
all Python operations are automatically checked for errors, with
appropriate action taken. </p>
<h3><a class="mozTocH3" name="mozTocId401576"></a>
<a name="ExprSyntaxDifferences"></a>Differences
between C
and Pyrex
expressions</h3>
There
are some differences in syntax and semantics between C expressions and
Pyrex expressions, particularly in the area of C constructs which have
no direct equivalent in Python.<br>
<ul>
<li>An integer literal without an <span style="font-family: monospace; font-weight: bold;">L</span>
suffix is treated as a C constant, and will be truncated to whatever
size your C compiler thinks appropriate. With an <span style="font-family: monospace; font-weight: bold;">L</span>
suffix, it will be converted to Python long integer (even if it would
be small enough to fit into a C int).<br>
<br>
</li>
<li>There is no <b><tt>-></tt></b>
operator
in Pyrex. Instead of <tt>p->x</tt>, use <tt>p.x</tt></li>
<li> There is no <b><tt>*</tt></b>
operator in Pyrex. Instead of <tt>*p</tt>, use <tt>p[0]</tt></li>
<li> There is an <b><tt>&</tt></b>
operator, with the same semantics as in C.</li>
<li>
The null C pointer is called <b><tt>NULL</tt></b>,
not 0 (and <tt>NULL</tt> is a reserved word).</li>
<li> Character literals are written with a <b>c</b>
prefix, for
example:</li>
<ul>
<pre>c'X'</pre>
</ul>
<li>Type casts are written <b><tt><type>value</tt></b>
, for example:</li>
<ul>
<pre>cdef char *p, float *q<br>p = <char*>q</pre>
</ul>
<i><b>Warning</b>:
Don't attempt to use a typecast to convert between
Python and C data types -- it won't do the right thing. Leave Pyrex to
perform the conversion automatically.</i>
</ul>
<h4>Operator Precedence</h4>
Keep in mind that there are
some differences
in operator precedence between Python and C, and that Pyrex uses the
Python precedences, not the C ones.
<h3><a class="mozTocH3" name="mozTocId899067"></a>Integer
for-loops</h3>
You should be aware that a for-loop such as
<blockquote><tt>for
i in range(n):</tt> <br>
<tt>
...</tt></blockquote>
won't be very fast, even if <tt>i</tt>
and <tt>n</tt> are declared as
C integers, because <tt>range</tt> is a Python function.
For iterating over ranges of integers, Pyrex has another form of
for-loop:
<blockquote><tt>for 0 <= i
< n:</tt> <br>
<tt>
...</tt></blockquote>
Provided the loop variable and the lower
and upper bounds are all C integers, this form of loop will be much
faster, because Pyrex will translate it into pure C code.
<p>Some
things to note about the integer for-loop: </p>
<ul>
<li> The target expression (the middle one) must be a variable
name.</li>
<li>The direction of iteration is
determined by the relations. If they are both from the set {<tt><</tt>,
<tt><=</tt>} then it is upwards; if they are
both
from the set {<tt>></tt>, <tt>>=</tt>}
then it is
downwards. (Any other combination is disallowed.)</li>
</ul>
Like other Python looping statements, <tt>break</tt> and <tt>continue</tt>
may be used in the body, and the loop may have an <tt>else</tt>
clause.
<h3><a class="mozTocH3" name="mozTocId457396"></a>Catching
exceptions and tracebacks</h3>
For
reasons of efficiency, there are some differences between Pyrex and
Python concerning the way exceptions caught by a try-except statement
are handled.<br>
<ul>
<li>Exceptions caught by an <span style="font-family: monospace;">except</span> clause <span style="font-style: italic;">cannot</span> be retrieved
using <span style="font-family: monospace;">sys.exc_info()</span>.
To access the caught exception, you must bind it to a name in the
except clause.<br><br>Pyrex also allows an additional name to be provided for
catching the traceback. For example,</li>
</ul>
<pre style="margin-left: 80px;">try:<br> start_engine()<br>except HovercraftError, e, tb:<br> print "Got an error:", e<br> traceback.print_tb(tb)</pre>
<ul>
<li>A <span style="font-family: monospace;">raise</span>
statement with no arguments (to re-raise the last exception caught)
must be lexically enclosed in the <span style="font-family: monospace;">except</span> clause
which caught the exception. A raise statement in a Python function
called from the except clause will <span style="font-style: italic;">not</span>
work.</li>
</ul>
<pre style="margin-left: 80px;">try:<br> start_engine()<br>except HovercraftError, e:<br> print "Unable to start:", e<br> raise # the exception caught by the enclosing except clause</pre>
<h2><a class="mozTocH2" name="mozTocId329136"></a>
<hr width="100%"></h2>
<h2><a class="mozTocH2" name="mozTocId482761"></a><a name="ExceptionValues"></a>Error return values</h2>
If you don't do anything special, a function declared with <b>cdef</b>
that does not return a Python object has no way of reporting Python
exceptions to its caller. If an exception is detected in such a
function, a warning message is printed and the exception is ignored.
<p>If
you want a C function that does not return a Python object to be able
to propagate exceptions to its caller, you need to declare an <b>exception
value</b> for it. Here is an example: </p>
<blockquote><tt>cdef
int spam() except -1:</tt> <br>
<tt>
...</tt></blockquote>
With this declaration, whenever an
exception occurs inside <tt>spam</tt>, it will immediately
return with the value <tt>-1</tt>. Furthermore, whenever a
call to <tt>spam</tt> returns <tt>-1</tt>, an
exception will be assumed to have occurred and will be propagated.
<p>When
you declare an exception value for a function, you should never
explicitly return that value. If all possible return values are legal
and you can't
reserve one entirely for signalling errors, you can use an alternative
form
of exception value declaration: </p>
<blockquote><tt>cdef
int spam() except? -1:</tt> <br>
<tt>
...</tt></blockquote>
The "?" indicates that the value <tt>-1</tt>
only indicates a <i>possible</i> error. In this case,
Pyrex generates a call to <tt>PyErr_Occurred</tt> if the
exception value is returned, to make sure it really is an error.
<p>There
is also a third form of exception value declaration: </p>
<blockquote><tt>cdef
int spam() except *:</tt> <br>
<tt>
...</tt></blockquote>
This form causes Pyrex to generate a
call to <tt>PyErr_Occurred</tt> after <i>every</i>
call to <code>spam</code>, regardless of what value it
returns. If you have a function returning <tt>void</tt>
that needs to propagate errors, you will have to use this form, since
there isn't any return value to test.
<p>Some things to note: </p>
<ul>
<li>Exception values can only declared for functions
returning an integer, enum, float or pointer type, and the value must
be a constant expression. The only possible pointer exception value is <tt>NULL</tt>.
Void functions can only use the <tt>except *</tt> form.</li>
<li> The exception value specification is part of the
signature
of the function. If you're passing a pointer to a function as a
parameter
or assigning it to a variable, the declared type of the parameter or
variable must have the same exception value specification (or lack
thereof). Here
is an example of a pointer-to-function declaration with an exception
value:</li>
<ul>
<pre><tt>int (*grail)(int, char *) except -1</tt></pre>
</ul>
<li>You don't need to (and shouldn't) declare exception values
for
functions which return Python objects. Remember that a function with no
declared return type implicitly returns a Python object.</li>
</ul>
<h3><a class="mozTocH3" name="mozTocId622828"></a>
<a name="CheckingReturnValues"></a>Checking
return values of non-Pyrex functions</h3>
It's important to
understand that the <tt>except</tt> clause does <i>not</i>
cause an error to be <i>raised</i> when the specified
value is returned. For
example, you can't write something like
<blockquote>
<pre>cdef extern FILE *fopen(char *filename, char *mode) except NULL <font color="#ed181e"># WRONG!</font></pre>
</blockquote>
and expect an exception to be automatically raised if a call to fopen
returns NULL. The except clause doesn't work that way; its only purpose
is for <i>propagating</i> exceptions that have already
been raised, either
by a Pyrex function or a C function that calls Python/C API routines.
To
get an exception from a non-Python-aware function such as fopen, you
will
have to check the return value and raise it yourself, for example,
<blockquote>
<pre>cdef FILE *p<br>p = fopen("spam.txt", "r")<br>if p == NULL:<br> raise SpamError("Couldn't open the spam file")</pre>
</blockquote>
<h4>
<hr width="100%"></h4>
<h2><a class="mozTocH2" name="mozTocId494354"></a>
<a name="IncludeStatement"></a>The <tt>include</tt>
statement</h2>
A Pyrex source file can include material from other files
using the <b>include</b>
statement, for example
<blockquote>
<pre>include "spamstuff.pxi"</pre>
</blockquote>
The contents of the named file are textually
included at that point. The included file can contain any complete
statements or declarations that are valid in the context where the
include statement appears, including other <b>include</b>
statements. The contents of the included file should begin at an
indentation level of zero, and will be treated as though they were
indented to the level of the include statement that is including the
file.<br>
<br>
Note
that there are other mechanisms available for splitting Pyrex code into
separate parts that may be more appropriate in many cases. See<a href="sharing.html"> Sharing Declarations Between
Pyrex Modules</a>.<br>
<hr style="width: 100%; height: 2px;">
<h2><a class="mozTocH2" name="mozTocId849661"></a><a name="KeywordOnlyArguments"></a>Keyword-only arguments</h2>
<p>Python
functions can have keyword-only arguments listed after the * parameter
and before the ** paramter if any, e.g.</p>
<pre style="margin-left: 40px;">def f(a, b, *args, c, d = 42, e, **kwds):<br> ...<br></pre>
Here
c, d and e cannot be passed as position arguments and must be passed as
keyword arguments. Furthermore, c and e are required keyword arguments,
since they do not have a default value.<br>
<br>
If the
parameter name after the * is omitted, the function will not accept any
extra positional arguments, e.g.<br>
<br>
<pre style="margin-left: 40px;">def g(a, b, *, c, d):<br> ...<br></pre>
takes
exactly two positional parameters and has two required keyword
parameters.<br>
<br>
<hr style="width: 100%; height: 2px;">
<h2><a class="mozTocH2" name="mozTocId829237"></a><a name="Built-in_Names"></a>Built-in Names</h2>
Pyrex
knows about many of the names in the builtin namespace, and treats them
specially in the interests of generating efficient code.<br>
<h3><a class="mozTocH3" name="mozTocId813519"></a><a name="Built-in_Constants"></a>Built-in Constants</h3>
Pyrex
knows the following built-in constant and type names, and references
their values directly instead of using a dictionary lookup.<br>
<br>
<table style="background-color: rgb(204, 255, 255); width: 10px; margin-left: 40px;" border="1" cellpadding="5" cellspacing="0">
<tbody>
<tr>
<td style="vertical-align: top; white-space: nowrap; text-align: left; background-color: rgb(255, 204, 0);">Type
objects (type <span style="font-family: monospace;">type</span>)</td>
<td colspan="2" rowspan="1" style="vertical-align: top; white-space: nowrap; text-align: left; background-color: rgb(255, 204, 0);">Exceptions
(type <span style="font-family: monospace;">type</span>)</td>
</tr>
<tr>
<td style="vertical-align: top; white-space: nowrap; text-align: left; height: 10px;">buffer<br>
enumerate<br>
file<br>
float<br>
int<br>
long<br>
open<br>
property<br>
str<br>
tuple<br>
xrange</td>
<td colspan="1" rowspan="3" align="left" nowrap="nowrap" valign="top">Exception<br>
StopIteration<br>
StandardError<br>
ArithmeticError<br>
LookupError<br>
AsssertionError<br>
EOFError<br>
FloatingPointError<br>
EnvironmentError<br>
IOError<br>
OSError<br>
ImportError<br>
IndexError<br>
KeyError<br>
KeyboardInterrupt<br>
MemoryError<br>
NameError<br>
OverflowError<br>
RuntimeError<br>
NotImplementedError<br>
SyntaxError</td>
<td colspan="1" rowspan="3" style="vertical-align: top; white-space: nowrap; text-align: left;">IndentationError<br>
TabError<br>
ReferenceError<br>
SystemError<br>
SystemExit<br>
TypeError<br>
UnboundLocalError<br>
UnicodeError<br>
UnicodeEncodeError<br>
UnicodeDecodeError<br>
UnicodeTranslateError<br>
ValueError<br>
ZeroDivisionError<br>
Warning<br>
UserWarning<br>
DeprecationWarning<br>
PendingDeprecationWarning<br>
SyntaxWarning<br>
OverflowWarning<br>
RuntimeWarning<br>
FutureWarning</td>
</tr>
<tr>
<td style="vertical-align: top; white-space: nowrap; text-align: left; height: 10px; background-color: rgb(255, 204, 0);">Constants
(type <span style="font-family: monospace;">object</span>)</td>
</tr>
<tr>
<td align="left" nowrap="nowrap" valign="top">True<br>
False<br>
Ellipsis</td>
</tr>
<tr>
</tr>
<tr>
</tr>
<tr>
</tr>
<tr>
</tr>
<tr>
</tr>
<tr>
</tr>
<tr>
</tr>
<tr>
</tr>
<tr>
</tr>
<tr>
</tr>
<tr>
</tr>
<tr>
</tr>
</tbody>
</table>
<br>
Note that although some of the above names refer to type objects, they
are not Pyrex type names and therefore can't be used to declare the
type of a variable. Only the names listed under Built-in Types below
can be used as type names in declarations.<br>
<h3><a class="mozTocH3" name="mozTocId593628"></a><a name="Built-in_Functions"></a>Built-in Functions</h3>
Pyrex
compiles calls to the following built-in functions into direct calls to
the corresponding Python/C API routines, making them particularly fast.<br>
<br>
<table style="text-align: left; background-color: rgb(204, 255, 255); margin-left: 40px;" border="1" cellpadding="4" cellspacing="0">
<tbody>
<tr>
<td style="font-weight: bold; background-color: rgb(255, 204, 51);">Function
and arguments</td>
<td style="font-weight: bold; background-color: rgb(255, 204, 51);">Return
type</td>
<td style="font-weight: bold; white-space: nowrap; background-color: rgb(255, 204, 51);">Python/C
API Equivalent</td>
</tr>
<tr>
<td>abs(obj)</td>
<td>object</td>
<td>PyNumber_Absolute</td>
</tr>
<tr>
<td align="left" nowrap="nowrap" valign="top">bool(obj)
<span style="font-style: italic;">(Note 3)</span></td>
<td align="left" nowrap="nowrap" valign="top">int</td>
<td align="left" nowrap="nowrap" valign="top">PyObject_IsTrue</td>
</tr>
<tr>
<td>delattr(obj, name)</td>
<td>int</td>
<td>PyObject_DelAttr</td>
</tr>
<tr>
<td>dir(obj)</td>
<td>object</td>
<td>PyObject_Dir</td>
</tr>
<tr>
<td>divmod(x, y)</td>
<td>object</td>
<td>PyNumber_Divmod</td>
</tr>
<tr>
<td style="white-space: nowrap;">getattr(obj, name)
<span style="font-style: italic;"> (Note 1</span>)<br>
getattr3(obj, name, default)</td>
<td>object</td>
<td>PyObject_GetAttr</td>
</tr>
<tr>
<td>hasattr(obj, name)</td>
<td>int</td>
<td>PyObject_HasAttr</td>
</tr>
<tr>
<td>hash(obj)</td>
<td>int</td>
<td>PyObject_Hash</td>
</tr>
<tr>
<td>cintern(char *)<span style="font-style: italic;">
(Note 5)</span></td>
<td>object</td>
<td>PyString_InternFromString</td>
</tr>
<tr>
<td>isinstance(obj, type)</td>
<td>int</td>
<td>PyObject_IsInstance</td>
</tr>
<tr>
<td>issubclass(obj, type)</td>
<td>int</td>
<td>PyObject_IsSubclass</td>
</tr>
<tr>
<td align="left" nowrap="nowrap" valign="top">issubtype(type,
type) <span style="font-style: italic;">(Note 4</span>)</td>
<td align="left" nowrap="nowrap" valign="top">int</td>
<td align="left" nowrap="nowrap" valign="top">PyType_IsSubType</td>
</tr>
<tr>
<td>iter(obj)</td>
<td>object</td>
<td>PyObject_GetIter</td>
</tr>
<tr>
<td align="left" nowrap="nowrap" valign="top">iter2(obj,
obj)</td>
<td align="left" nowrap="nowrap" valign="top">object</td>
<td align="left" nowrap="nowrap" valign="top">PyCallIter_New</td>
</tr>
<tr>
<td>len(obj)</td>
<td>Py_ssize_t</td>
<td>PyObject_Length</td>
</tr>
<tr>
<td style="width: 1px;">pow(x, y, z) <span style="font-style: italic;"> (Note 2)</span></td>
<td style="width: 1px;">object</td>
<td style="width: 1px;">PyNumber_Power</td>
</tr>
<tr>
<td>reload(obj)</td>
<td>object</td>
<td>PyImport_ReloadModule</td>
</tr>
<tr>
<td>repr(obj)</td>
<td>object</td>
<td>PyObject_Repr</td>
</tr>
<tr>
<td style="width: 200px;">setattr(obj, name)</td>
<td style="width: 100px;">void</td>
<td style="width: 150px;">PyObject_SetAttr</td>
</tr>
<tr>
<td align="left" nowrap="nowrap" valign="top">typecheck(obj,
type) <span style="font-style: italic;">(Note
4)</span></td>
<td align="left" nowrap="nowrap" valign="top">int</td>
<td align="left" nowrap="nowrap" valign="top">PyObject_TypeCheck</td>
</tr>
</tbody>
</table>
<br>
<div style="margin-left: 40px;"><span style="font-style: italic;">Note 1:</span> There are
two different functions corresponding to the Python <span style="font-family: monospace;">getattr</span>
depending on whether a third argument is used. In a non-call context,
they both evaluate to the Python <span style="font-family: monospace;">getattr</span>
function.<br>
<br>
<span style="font-style: italic;">Note 2:</span>
Only the three-argument form of <span style="font-family: monospace;">pow()</span> is
supported. Use the <span style="font-family: monospace;">**</span>
operator otherwise.<br>
<br>
<span style="font-style: italic;">Note 3:</span> In
a non-call context, the name <span style="font-family: monospace;">bool</span>
refers to the Python built-in bool type.<br>
<br>
<span style="font-style: italic;">Note 4:</span> The
functions <span style="font-family: monospace;">typecheck</span>
and <span style="font-family: monospace;">issubtype</span>
have no exact Python equivalent. They are included for fast, safe type
checking of extension types. They are safer than using <span style="font-family: monospace;">isinstance</span> and <span style="font-family: monospace;">issubclass</span>
for this purpose, because the behaviour of the latter functions can be
overridden, so they don't necessarily reflect the true C types of the
objects involved.<br>
<br>
<span style="font-style: italic;">Note 5:</span>
This function is named <span style="font-family: monospace;">cintern</span>
instead of <span style="font-family: monospace;">intern</span>
because it takes a null-terminated C string rather than a Python
string, and therefore cannot handle strings containing null bytes.<br>
</div>
<br>
Only
direct function calls using these names are optimised. If you do
something else with one of these names that assumes it's a Python
object, such as assign it to a Python variable, and later call it, the
call will be made as a Python function call.
<h3><a class="mozTocH3" name="mozTocId452377"></a><a name="BuiltinTypes"></a>Built-in Types</h3>
Pyrex
knows about the following builtin
types:<br>
<br>
<div style="margin-left: 40px;"><span style="font-family: monospace;">dict</span><br style="font-family: monospace;">
<span style="font-family: monospace;">list</span><br>
<span style="font-family: monospace;">object</span><br style="font-family: monospace;">
<span style="font-family: monospace;">slice</span><br style="font-family: monospace;">
<span style="font-family: monospace;">type</span><br>
</div>
<br>
If you declare a variable as being of one of these types, then
calls to the methods in the table below will be compiled to direct
Python/C API calls,
avoiding the overhead of a Python attribute lookup and function call.
In the case of attributes, they will be accessed directly from the
object's C struct.<br>
<br>
Referring to the types themselves is also
slightly more efficient, because the relevant type object is accessed
directly rather than via a global variable lookup.<br>
<br>
<table style="text-align: left; background-color: rgb(204, 255, 255); width: 665px; height: 330px;" border="1" cellpadding="4" cellspacing="0">
<tbody>
<tr>
<td style="font-weight: bold; background-color: rgb(255, 204, 51);">Method
or Attribute</td>
<td style="font-weight: bold; background-color: rgb(255, 204, 51);">Return
type</td>
<td colspan="1" rowspan="1" style="font-weight: bold; white-space: nowrap; background-color: rgb(255, 204, 51);">Python/C
API Equivalent</td>
<td style="background-color: rgb(255, 204, 51); font-weight: bold;" align="left" nowrap="nowrap">Notes</td>
</tr>
<tr>
<td colspan="4" rowspan="1" style="vertical-align: top; white-space: nowrap; text-align: left; background-color: rgb(51, 153, 153);"><span style="font-weight: bold;">Type </span><span style="font-family: monospace; font-weight: bold;">dict</span></td>
</tr>
<tr>
<td align="left" nowrap="nowrap" valign="top">clear()</td>
<td align="left" nowrap="nowrap" valign="top"></td>
<td align="left" nowrap="nowrap" valign="top">PyDict_Clear</td>
<td align="left" nowrap="nowrap" valign="top"></td>
</tr>
<tr>
<td align="left" nowrap="nowrap" valign="top">copy()</td>
<td align="left" nowrap="nowrap" valign="top"></td>
<td align="left" nowrap="nowrap" valign="top">PyDict_Copy</td>
<td align="left" nowrap="nowrap" valign="top"></td>
</tr>
<tr>
<td align="left" nowrap="nowrap" valign="top">items()</td>
<td align="left" nowrap="nowrap" valign="top">object</td>
<td align="left" nowrap="nowrap" valign="top">PyDict_Items</td>
<td align="left" nowrap="nowrap" valign="top"></td>
</tr>
<tr>
<td align="left" nowrap="nowrap" valign="top">keys()</td>
<td align="left" nowrap="nowrap" valign="top">object</td>
<td align="left" nowrap="nowrap" valign="top">PyDict_Keys</td>
<td align="left" nowrap="nowrap" valign="top"></td>
</tr>
<tr>
<td align="left" nowrap="nowrap" valign="top">values()</td>
<td align="left" nowrap="nowrap" valign="top">object</td>
<td align="left" nowrap="nowrap" valign="top">PyDict_Values</td>
<td align="left" nowrap="nowrap" valign="top"></td>
</tr>
<tr>
<td align="left" nowrap="nowrap" valign="top">merge(obj,
override)</td>
<td align="left" nowrap="nowrap" valign="top"></td>
<td align="left" nowrap="nowrap" valign="top">PyDict_Merge</td>
<td align="left" nowrap="nowrap" valign="top">Merge
items from a mapping</td>
</tr>
<tr>
<td align="left" nowrap="nowrap" valign="top">update(obj)</td>
<td align="left" nowrap="nowrap" valign="top"></td>
<td align="left" nowrap="nowrap" valign="top">PyDict_Update</td>
<td align="left" nowrap="nowrap" valign="top"></td>
</tr>
<tr>
<td align="left" nowrap="nowrap" valign="top">merge_pairs(obj, override)</td>
<td align="left" nowrap="nowrap" valign="top"></td>
<td align="left" nowrap="nowrap" valign="top">PyDict_MergeFromSeq2</td>
<td align="left" nowrap="nowrap" valign="top">Merge
(key, value) pairs from a sequence</td>
</tr>
<tr>
<td colspan="4" rowspan="1" style="vertical-align: top; white-space: nowrap; text-align: left; background-color: rgb(51, 153, 153);"><span style="font-weight: bold;">Type </span><span style="font-family: monospace; font-weight: bold;">list</span></td>
</tr>
<tr>
<td align="left" nowrap="nowrap" valign="top">insert(int,
obj)</td>
<td align="left" nowrap="nowrap" valign="top"></td>
<td align="left" nowrap="nowrap" valign="top">PyList_Insert</td>
<td align="left" nowrap="nowrap" valign="top"></td>
</tr>
<tr>
<td align="left" nowrap="nowrap" valign="top">append(obj)</td>
<td align="left" nowrap="nowrap" valign="top"></td>
<td align="left" nowrap="nowrap" valign="top">PyList_Append</td>
<td align="left" nowrap="nowrap" valign="top"></td>
</tr>
<tr>
<td align="left" nowrap="nowrap" valign="top">sort()</td>
<td align="left" nowrap="nowrap" valign="top"></td>
<td align="left" nowrap="nowrap" valign="top">PyList_Sort</td>
<td align="left" nowrap="nowrap" valign="top"></td>
</tr>
<tr>
<td align="left" nowrap="nowrap" valign="top">reverse()</td>
<td align="left" nowrap="nowrap" valign="top"></td>
<td align="left" nowrap="nowrap" valign="top">PyList_Reverse</td>
<td align="left" nowrap="nowrap" valign="top"></td>
</tr>
<tr>
<td align="left" nowrap="nowrap" valign="top">as_tuple()</td>
<td align="left" nowrap="nowrap" valign="top">object</td>
<td align="left" nowrap="nowrap" valign="top">PyList_AsTuple</td>
<td align="left" nowrap="nowrap" valign="top"></td>
</tr>
<tr>
<td colspan="4" rowspan="1" style="vertical-align: top; white-space: nowrap; text-align: left; background-color: rgb(51, 153, 153);"><span style="font-weight: bold;">Type <span style="font-family: monospace;">slice</span></span></td>
</tr>
<tr>
<td align="left" nowrap="nowrap" valign="top">indices()</td>
<td align="left" nowrap="nowrap" valign="top">object</td>
<td align="left" nowrap="nowrap" valign="top">PySlice_Indices</td>
<td align="left" nowrap="nowrap" valign="top"></td>
</tr>
<tr>
<td align="left" nowrap="nowrap" valign="top">start</td>
<td align="left" nowrap="nowrap" valign="top">object</td>
<td align="left" nowrap="nowrap" valign="top"></td>
<td align="left" nowrap="nowrap" valign="top"></td>
</tr>
<tr>
<td align="left" nowrap="nowrap" valign="top">stop</td>
<td align="left" nowrap="nowrap" valign="top">object</td>
<td align="left" nowrap="nowrap" valign="top"></td>
<td align="left" nowrap="nowrap" valign="top"></td>
</tr>
<tr>
<td align="left" nowrap="nowrap" valign="top">step</td>
<td align="left" nowrap="nowrap" valign="top">object</td>
<td align="left" nowrap="nowrap" valign="top"></td>
<td align="left" nowrap="nowrap" valign="top"></td>
</tr>
</tbody>
</table>
<br>
Some
of the above methods have no direct Python equivalent, but are there to
provide access to routines that exist in the Python/C API.<br>
<br>
As an example, the following compiles into code containing no Python
attribute lookups or function calls.<br>
<br>
<div style="margin-left: 40px;"><span style="font-family: monospace;">cdef list cheeses</span><br style="font-family: monospace;">
<span style="font-family: monospace;">cheeses = []</span><br style="font-family: monospace;">
<span style="font-family: monospace;">cheeses.append("camembert")</span><br style="font-family: monospace;">
<span style="font-family: monospace;">cheeses.append("cheddar")</span><br style="font-family: monospace;">
<span style="font-family: monospace;">cheeses.insert(1,
"something runny")</span><br style="font-family: monospace;">
</div>
<br>
<hr style="width: 100%; height: 2px;">
<h2><a class="mozTocH2" name="mozTocId42018"></a><a name="Conditional_Compilation"></a>Conditional
Compilation</h2>
Some features are available for conditional compilation and
compile-time constants within a Pyrex source file.<br>
<h3><a class="mozTocH3" name="mozTocId379306"></a><a name="Compile-Time_Definitions"></a>Compile-Time
Definitions</h3>
A compile-time constant can be defined using the <span style="font-family: monospace; font-weight: bold;">DEF</span>
statement:<br>
<pre style="margin-left: 40px;">DEF FavouriteFood = "spam"<br>DEF ArraySize = 42<br>DEF OtherArraySize = 2 * ArraySize + 17</pre>
The
right-hand side of the DEF must be a valid compile-time expression.
Such expressions are made up of literal values and names defined using
DEF statements, combined using any of the Python expression syntax.<br>
<br>
The following compile-time names are predefined, corresponding to the
values returned by <span style="font-weight: bold;">os.uname()</span>.<br>
<pre style="margin-left: 40px;">UNAME_SYSNAME, UNAME_NODENAME, UNAME_RELEASE,<br>UNAME_VERSION, UNAME_MACHINE</pre>
The following selection of builtin constants and functions are also
available:<br>
<pre style="margin-left: 40px;">None, True, False,<br>abs, bool, chr, cmp, complex, dict, divmod, enumerate,<br>float, hash, hex, int, len, list, long, map, max, min,<br>oct, ord, pow, range, reduce, repr, round, slice, str,<br>sum, tuple, xrange, zip</pre>
A
name defined using DEF can be used anywhere an identifier can appear,
and it is replaced with its compile-time value as though it were
written into the source at that point as a literal. For this to work,
the compile-time expression must evaluate to a Python value of type <span style="font-weight: bold;">int</span>, <span style="font-weight: bold;">long</span>, <span style="font-weight: bold;">float </span>or <span style="font-weight: bold;">str</span>.<br>
<pre style="margin-left: 40px;">cdef int a1[ArraySize]<br>cdef int a2[OtherArraySize]<br>print "I like", FavouriteFood</pre>
<h3><a class="mozTocH3" name="mozTocId997015"></a><a name="Conditional_Statements"></a>Conditional
Statements</h3>
The <span style="font-family: monospace; font-weight: bold;">IF</span>
statement can be used to conditionally include or exclude sections of
code at compile time. It works in a similar way to the <span style="font-weight: bold;">#if</span> preprocessor
directive in C.<br>
<pre style="margin-left: 40px;">IF UNAME_SYSNAME == "Windows":<br> include "icky_definitions.pxi"<br>ELIF UNAME_SYSNAME == "Darwin":<br> include "nice_definitions.pxi"<br>ELIF UNAME_SYSNAME == "Linux":<br> include "penguin_definitions.pxi"<br>ELSE:<br> include "other_definitions.pxi"</pre>
The
ELIF and ELSE clauses are optional. An IF statement can appear anywhere
that a normal statement or declaration can appear, and it can contain
any statements or declarations that would be valid in that context,
including DEF statements and other IF statements.<br>
<br>
The
expressions in the IF and ELIF clauses must be valid compile-time
expressions as for the DEF statement, although they can evaluate to any
Python value, and the truth of the result is determined in the usual
Python way.<br>
<br>
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