.. [#] The conversion is to/from str for Python 2.x, and bytes for Python 3.x.
.. note::
**Python String in a C Context**
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@@ -360,24 +353,24 @@ Automatic Type Conversion
**It is up to you to be aware of this, and not to depend on Cython's error message, as it is not guarenteed to be generated for every situation.**
Type Casting
=============
* The syntax used in type casting are ``"<"`` and ``">"``, for example::
* The syntax used in type casting are ``"<"`` and ``">"``
cdef char *p, float *q
p = <char*>q
.. note::
The syntax is different from C convention
::
* .. note:: that this is different from C convention.
cdef char *p, float *q
p = <char*>q
* If exactly one of the types is a python object for ``<type>x``, Cython will try and do a coersion.
* If one of the types is a python object for ``<type>x``, Cython will try and do a coersion.
* .. note:: Cython will not stop a casting where there is no conversion, but it will emit a warning.
.. note:: Cython will not stop a casting where there is no conversion, but it will emit a warning.
* If the address is what is wanted, cast to a ``void*`` first.
* If the address is what is wanted, cast to a ``void*`` first.
Type Checking
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@@ -454,8 +447,6 @@ Scope Rules
True = 1
=====================
Functions and Methods
=====================
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@@ -488,13 +479,98 @@ Overriding
Function Pointers
=================
Functions declared in a ``struct`` are automatically converted to function pointers.
* Functions declared in a ``struct`` are automatically converted to function pointers.
* see **using exceptions with function pointers**
============================
Error and Exception Handling
============================
* A plain ``cdef`` declared function, that does not return a Python object...
* Has no way of reporting a Python exception to it's caller.
* Will only print a warning message and the exception is ignored.
* Inorder to propagate exceptions like this to it's caller, you need to declare an exception value for it.
* There are three forms of declaring an exception for a C compiled program.
* First::
cdef int spam() except -1:
...
* In the example above, if an error occurs inside spam, it will immediately return with the value of ``-1``, causing an exception to be propagated to it's caller.
* Functions declared with an exception value, should explicitly prevent a return of that value.
* Second::
cdef int spam() except? -1:
...
* Used when a ``-1`` may possibly be returned and is not to be considered an error.
* The ``"?"`` tells Cython that ``-1`` only indicates a *possible* error.
* Now, each time ``-1`` is returned, Cython generates a call to ``PyErr_Occurrd`` to verify it is an actual error.
* Third::
cdef int spam() except +
* A call to ``PyErr_Occurred`` happens *every* time the function gets called.
.. note:: Returning ``void``
A need to propagate errors when returning ``void`` must use this version.
* Exception values can only be declared for functions returning an..
* integer
* enum
* float
* pointer type
* Must be a constant expression
.. note::
.. note:: Function pointers
* Require the same exception value specification as it's user has declared.
* Use cases here are when used as parameters and when assigned to a variable
* Example::
int (*grail)(int, char *) except -1
.. note:: Python Objects
* Declared exception values are **not** need.
* Remember that Cython assumes that a function function without a declared return value, returns a Python object.
* Exceptions on such functions are implicitly propagated by returning ``NULL``
.. note:: C++
For exceptions from C++ compiled programs, see **Wrapping C++ Classes**
Checking return values for non-Cython functions..
=================================================
* Do not try to raise exceptions by returning the specified value.. Example::
