[Pyinline-discuss] PyInline FAQ

[Ken S. <ksi...@tt...>]

Jeff Youel posted some interesting questions in his recent Ethernet MAC
address script (the first publicly announced script to use PyInline! --
see it at http://www.jeffyouel.com), which I have paraphrased in this
email. Perhaps other PyInliners out there could help me find answers to
Jeff's questions.

1. How do I raise Python exceptions from PyInline'd C code?

To generate exceptions from your inlined Python functions, you must do
some of the inlining legwork yourself. Rather than returning one of the
standard C data types from your function, you must return a PyObject* and
set up the return value using Py_BuildValue() or one of the other
value-building functions in the Python C API. When you want to throw an
exception, just call PyErr_SetString() or one of the other exception
"throwing" functions and return NULL.

For example, the following bit of Python defines a C function that adds
two numbers together and returns the result, but which fires an exception
if the result is zero.

import PyInline

m = PyInline.build(code=r"""
PyObject* add(int a, int b) {
  PyObject* retval;
  int sum = a + b;

  if(sum == 0) {
    PyErr_SetString(PyExc_ValueError, "Sum must not be zero!");
    return NULL;
  }

  else {
    retval = Py_BuildValue("i", sum);
    return retval;
  }
}
""", language="C")

print m.add(10, 5)   # Okay
print m.add(10, -10) # Throws an exception.


2. How do I return dynamically allocated strings without leaking memory?

Probably the easiest way to return a dynamically allocated string is to
just return a PyObject* from your PyInlined function. For example,

import PyInline

m = PyInline.build(code=r"""
PyObject* genstring(void) {
  PyObject* retval = Py_BuildValue("s", "This is my special string.");
  return retval;
}
""", language="C")

str = m.genstring()
print str

PyInline knows that if you return a PyObject* from your inlined C
function, the PyObject* should just be passed verbatim back to Python.

3. How can I ship my inline Python script along with its compiled
binary extensions?

Currently, the only way to ship the binary part of your inline script is
to first run the script on your system to generate and compile any inlined
C source code and then ship the _PyInline_abc34234... directory along with
your script.

I am currently discussing this problem with Brian Ingerson (of Inline for
Perl fame) and hope to have a better solution soon. Probably the new
solution will involve configuration files...

4. How do I keep from collecting dozens of _PyInline_* directories while
I'm developing?

Currently, "rm -r _PyInline*" is the most effective strategy to reduce
clutter. In future, PyInline will provide a configuration file inside a
much better-named directory (perhaps _PyInline_MyModuleName) which
contains the MD5 checksum of all inlined sources so that PyInline knows
when to do a rebuild.

TTUL
Ken

On Fri, 31 Aug 2001, Ken Simpson wrote:

> Hi Jeff,
> I was wondering whether you would mind if I added your PyInline MAC
> address script to the examples directory of PyInline?
>
> To my knowledge, your script is the first real-world use of PyInline!
>
> TTUL
> Ken
>
>