@@ -73,5 +73,5 @@ section of the <a href="extension_types.html">"Extension
Types"</a> documentation page.<br>
<h2><aname="Quack"></a>Python says my extension type has no method called 'quack', but I know it does. What gives?</h2>
You may have declared the method using <spanstyle="font-family: monospace;">cdef</span> instead of <spanstyle="font-family: monospace;">def</span>. Only functions and methods declared with <spanstyle="font-family: monospace;">def</span> are callable from Python code.<br>
@@ -35,7 +35,7 @@ The main difference is that you can use the :keyword:`cdef` statement to define
attributes. The attributes may be Python objects (either generic or of a
particular extension type), or they may be of any C data type. So you can use
extension types to wrap arbitrary C data structures and provide a Python-like
interface to them.
interface to them.
.. _readonly:
...
...
@@ -117,35 +117,35 @@ The same consideration applies to local variables, for example,::
Type Testing and Casting
------------------------
Suppose I have a method :meth:`quest` which returns an object of type :class:`Shrubbery`.
Suppose I have a method :meth:`quest` which returns an object of type :class:`Shrubbery`.
To access it's width I could write::
cdef Shrubbery sh = quest()
print sh.width
which requires the use of a local variable and performs a type test on assignment.
which requires the use of a local variable and performs a type test on assignment.
If you *know* the return value of :meth:`quest` will be of type :class:`Shrubbery`
you can use a cast to write::
print (<Shrubbery>quest()).width
This may be dangerous if :meth:`quest()` is not actually a :class:`Shrubbery`, as it
will try to access width as a C struct member which may not exist. At the C level,
rather than raising an :class:`AttributeError`, either an nonsensical result will be
This may be dangerous if :meth:`quest()` is not actually a :class:`Shrubbery`, as it
will try to access width as a C struct member which may not exist. At the C level,
rather than raising an :class:`AttributeError`, either an nonsensical result will be
returned (interpreting whatever data is at that address as an int) or a segfault
may result from trying to access invalid memory. Instead, one can write::
print (<Shrubbery?>quest()).width
which performs a type check (possibly raising a :class:`TypeError`) before making the
cast and allowing the code to proceed.
which performs a type check (possibly raising a :class:`TypeError`) before making the
cast and allowing the code to proceed.
To explicitly test the type of an object, use the :meth:`isinstance` method. By default,
in Python, the :meth:`isinstance` method checks the :class:`__class__` attribute of the
first argument to determine if it is of the required type. However, this is potentially
unsafe as the :class:`__class__` attribute can be spoofed or changed, but the C structure
of an extension type must be correct to access its :keyword:`cdef` attributes and call its :keyword:`cdef` methods. Cython detects if the second argument is a known extension
type and does a type check instead, analogous to Pyrex's :meth:`typecheck`.
To explicitly test the type of an object, use the :meth:`isinstance` method. By default,
in Python, the :meth:`isinstance` method checks the :class:`__class__` attribute of the
first argument to determine if it is of the required type. However, this is potentially
unsafe as the :class:`__class__` attribute can be spoofed or changed, but the C structure
of an extension type must be correct to access its :keyword:`cdef` attributes and call its :keyword:`cdef` methods. Cython detects if the second argument is a known extension
type and does a type check instead, analogous to Pyrex's :meth:`typecheck`.
The old behavior is always available by passing a tuple as the second parameter::
print isinstance(sh, Shrubbery) # Check the type of sh
...
...
@@ -207,7 +207,7 @@ with checking that it has the right type.
be ``None``.
* When comparing a value with ``None``, keep in mind that, if ``x`` is a Python
object, ``x is None`` and ``x is not None`` are very efficient because they
translate directly to C pointer comparisons, whereas ``x == None`` and
translate directly to C pointer comparisons, whereas ``x == None`` and
``x != None``, or simply using ``x`` as a boolean value (as in ``if x: ...``)
will invoke Python operations and therefore be much slower.
...
...
@@ -260,7 +260,7 @@ There is also a special (deprecated) legacy syntax for defining properties in an
def __del__(self):
# This is called when the property is deleted.
The :meth:`__get__`, :meth:`__set__` and :meth:`__del__` methods are all
optional; if they are omitted, an exception will be raised when the
...
...
@@ -269,7 +269,7 @@ corresponding operation is attempted.
Here's a complete example. It defines a property which adds to a list each
time it is written to, returns the list when it is read, and empties the list
when it is deleted.::
# cheesy.pyx
cdef class CheeseShop:
...
...
@@ -494,7 +494,7 @@ object called :attr:`__weakref__`. For example,::
cdef class ExplodingAnimal:
"""This animal will self-destruct when it is
no longer strongly referenced."""
cdef object __weakref__
...
...
@@ -546,7 +546,7 @@ can participate in cycles could cause memory leaks ::
cdef str name
cdef tuple addresses
If you can be sure addresses will contain only references to strings,
If you can be sure addresses will contain only references to strings,
the above would be safe, and it may yield a significant speedup, depending on
your usage pattern.
...
...
@@ -604,7 +604,7 @@ built-in complex object.::
2. As well as the name of the extension type, the module in which its type
object can be found is also specified. See the implicit importing section
below.
below.
3. When declaring an external extension type, you don't declare any
methods. Declaration of methods is not required in order to call them,
...
...
@@ -662,7 +662,7 @@ You can also specify an alternative name under which to import the type using
an as clause, for example,::
cdef extern class My.Nested.Package.Spam as Yummy:
...
...
which corresponds to the implicit import statement::
