Commit 5598db0e authored by Francesc Alted's avatar Francesc Alted Committed by Robert Bradshaw

Added compiler directives to the Compilation section.

parent 5db0a3f4
......@@ -2,31 +2,99 @@
.. _compilation:
Cython code, unlike Python, must be compiled. This happens in two stages:
* A ``.pyx`` file is compiles by Cython to a ``.c`` file.
* The ``.c`` file is compiled by a C comiler to a ``.so`` file (or a
* The ``.c`` file is compiled by a C compiler to a ``.so`` file (or a
``.pyd`` file on Windows)
You can tailor the behaviour of the Cython compiler by specifying the
directives below.
Compiler directives
Compiler directives are instructions which affect which sort of code
Cython generates. Here is the list:
``boundscheck`` (True / False)
If set to False, Cython is free to assume that indexing operations
([]-operator) in the code will not cause any IndexErrors to be
raised. Currently this is only made use of for buffers, but lists
and tuples could be affected in the future. Conditions which would
normally trigger an IndexError may instead cause segfaults or data
corruption if this is set to False. Default is True.
``wraparound`` (True / False)
In Python arrays can be indexed relative to the end. For example
A[-1] indexes the last value of a list. In C negative indexing is
not supported. If set to False, Cython will not ensure that python
indexing is not used. Default is True.
``nonecheck`` (True / False)
If set to False, Cython is free to assume that native field
accesses on variables typed as an extension type, or buffer
accesses on a buffer variable, never occurs when the variable is
set to ``None``. Otherwise a check is inserted and the
appropriate exception is raised. This is off by default for
performance reasons. Default is False.
``embedsignature`` (True / False)
If set to True, Cython will embed a textual copy of the call
signature in the docstring of all Python visible functions and
classes. Tools like IPython and epydoc can thus display the
signature, which cannot otherwise be retrieved after
compilation. Default is False.
``cdivision`` (True / False)
If set to False, Cython will adjust the remainder and quotient
operators C types to match those of Python ints (which differ when
the operands have opposite signs) and raise a
``ZeroDivisionError`` when the right operand is 0. This has about
a 35% speed penalty. If set to True, no checks are performed. See
`CEP 516 <>`. Default
is False.
``cdivision_warnings`` (True / False)
If set to True, Cython will emit a runtime warning whenever
division is performed with negative operands. See `CEP 516
<>`. Default is
``always_allow_keywords`` (True / False)
Avoid the ``METH_NOARGS`` and ``METH_O`` when constructing
functions/methods which take zero or one arguments. Has no effect
on special methods and functions with more than one argument. The
``METH_NOARGS`` and ``METH_O`` signatures provide faster
calling conventions but disallow the use of keywords.
``profile`` (True / False)
Add hooks for Python profilers into the compiled C code. Default
is False.
``infer_types`` (True / False)
Infer types of untyped variables in function bodies. Default is
The following sub-sections describe several ways to build your
extension modules.
extension modules, and how to pass directives to the Cython compiler.
From the Command Line
From the command line
Run the Cython compiler command with your options and list of ``.pyx``
files to generate. For example::
files to generate. For example::
$ cython -a yourmod.pyx
This creates a ``yourmod.c`` file (and the -a switch produces a
generated html file).
This creates a ``yourmod.c`` file, and the -a switch produces a
generated html file. Pass the ``-h`` flag for a complete list of
supported flags.
Compiling your ``.c`` files will vary depending on your operating
system. Python documentation for writing extension modules should
......@@ -41,7 +109,7 @@ paths to libraries you need to link with]
A ```` file is now in the same directory and your module,
``yourmod``, is available for you to import as you normally would.
......@@ -65,7 +133,6 @@ Run the command ``python build_ext --inplace`` in your
system's command shell and you are done. Import your new extension
module into your python shell or script as normal.
......@@ -89,7 +156,6 @@ using this feature, just tell that to ``pyximport``::
>>> pyximport.install(pyimport = True)
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