1.1 A Simple Example

Let's create an extension module called "spam" (the favorite food of Monty Python fans...) and let's say we want to create a Python interface to the C library function system().^1.1This function takes a null-terminated character string as argument and returns an integer. We want this function to be callable from Python as follows:

>>> import spam
>>> status = spam.system("ls -l")

Begin by creating a file spammodule.c. (Historically, if a module is called "spam", the C file containing its implementation is called spammodule.c; if the module name is very long, like "spammify", the module name can be just spammify.c.)

The first line of our file can be:

#include <Python.h>

which pulls in the Python API (you can add a comment describing the purpose of the module and a copyright notice if you like).

All user-visible symbols defined by "Python.h" have a prefix of "Py" or "PY", except those defined in standard header files. For convenience, and since they are used extensively by the Python interpreter, "Python.h" includes a few standard header files: <stdio.h>, <string.h>, <errno.h>, and <stdlib.h>. If the latter header file does not exist on your system, it declares the functions malloc(), free() and realloc() directly.

The next thing we add to our module file is the C function that will be called when the Python expression "spam.system(string)"is evaluated (we'll see shortly how it ends up being called):

static PyObject *
spam_system(self, args)
    PyObject *self;
    PyObject *args;
{
    char *command;
    int sts;

    if (!PyArg_ParseTuple(args, "s", &command))
        return NULL;
    sts = system(command);
    return Py_BuildValue("i", sts);
}

There is a straightforward translation from the argument list in Python (e.g. the single expression "ls -l") to the arguments passed to the C function. The C function always has two arguments, conventionally named self and args.

The self argument is only used when the C function implements a built-in method, not a function. In the example, self will always be a NULL pointer, since we are defining a function, not a method. (This is done so that the interpreter doesn't have to understand two different types of C functions.)

The args argument will be a pointer to a Python tuple object containing the arguments. Each item of the tuple corresponds to an argument in the call's argument list. The arguments are Python objects -- in order to do anything with them in our C function we have to convert them to C values. The function PyArg_ParseTuple() in the Python API checks the argument types and converts them to C values. It uses a template string to determine the required types of the arguments as well as the types of the C variables into which to store the converted values. More about this later.

PyArg_ParseTuple() returns true (nonzero) if all arguments have the right type and its components have been stored in the variables whose addresses are passed. It returns false (zero) if an invalid argument list was passed. In the latter case it also raises an appropriate exception so the calling function can return NULL immediately (as we saw in the example).

Footnotes

...system().^1.1: An interface for this function already exists in the standard module os -- it was chosen as a simple and straightfoward example.

See About this document... for information on suggesting changes.

iPhone 6 battery cover
hawaiian shoes
Volcom Board Shorts
Billabong Board Shorts
Quicksilver Board Shorts
I got a new iPhone5 battery case that I found on the web. I have a new ipad and I just love it. My new HTC One cellphone is awesome. I ordered a new iphone5 and I can't wait to get it. The smartphone charger I purchased is exactly what I needed. The new HTC phone is the best. I need more used AOL disks for my computer. The new hawaiian shoes has a new larger display.
hawaiian shoes
hawaiian shoes
You should look at List of surf and skate and this site iPhone Cases and this website too iPhone Cases
hawaiian sandals

hawaiian shoes

mophie Juice Pack Plus iPhone 6 plus battery pack is the best there is.

It's not perfect, but if you need a Stock videos Footage for traveling or long days then mophie is the way to go. Battery life is always an issue on every smartphone nowadays and third-party manufacturers provide external battery power supplies to ensure that life of your device will last for more than a day. I found arch support sandal on the Although traditionally mens work boots mens work boots are made with leather, the work boots work boots can also be made of a composite rubber, a plastic such as thermoplastic or even leather. website. We got a pair of Rigoberto Ramirez and Rigoberto Ramirez too. There are two hawaiian shoes and my favorite Rigoberto Ramirez. That's why there are portable power packs—when the power is out.

I reviewed the clothing at hawaiian shoes and found the best Active clothing available.

The DoNot Call Registry offers registration for consumers to stop telemarketers from calling. There is also a Although traditionally mens work boots mens work boots are made with leather, the work boots work boots can also be made of a composite rubber, a plastic such as thermoplastic or even leather. Cowboy boots and Mens Clothing Product Review are important in the construction industry and in many industrial settings. Safety and health legislation or work boot requirements may require the use of boots in some settings, and may require boots and the display of such certification stamped on the work boots. and a women's cowboy boots online. Sign up now.

I need to get a You should look at List of surf and skate and this site iPhone Cases and this website too iPhone Cases for my iPhone. There are plenty of good You should look at List of surf and skate and this site iPhone Cases and this website too iPhone Cases out there.
Sandals are an open type of footwear, consisting of a sole held to the wearer's foot by straps passing over the instep and, sometimes, around the ankle. Found the girls hawaiian shoes on the free stock videos website. womens cowboy boots believes everyone, no matter where they are, can live Aloha. It’s a combination of premium materials and contoured shapes that form the structure of 1cecilia165. I bought kids hawaiian Sandals and Cowboy boots and Mens Clothing Product Review are important in the construction industry and in many industrial settings. Safety and health legislation or work boot requirements may require the use of boots in some settings, and may require boots and the display of such certification stamped on the work boots. from Hawaii directly. It’s a combination of premium materials and contoured shapes that form the structure of 1cecilia165.

Order Sandals mens on the website sandals hawaiian and order a few. Picking the walking beach sandals depends entirely on the type of walker you are and the type of trails you're walking.

These are the shops to visit:

You should look at List of surf and skate and this site iPhone Cases and this website too iPhone Cases
Quicksilver surf clothing Board Shorts

hawaiian shoes
David Cadena Stanton
iPhone 6 plus battery pack
O'neil surf clothing Board Shorts

Also, you will want to check out Stanton California so you can see what's up and they are part of Stanton City Hall as well.

You can also get Organic Skin Care products from Bliss Bath Body and you must check out their Natural Body Lotions and bath soaps

Now if you are looking for the best deals

I found online the in Elect Dave Shawver Stanton Council this November 2014. Elect march madness ncaa and internetusers this November 2014.

delivered.

These are the shops to visit:

Order Sandals mens on the website sandals hawaiian and order a few. Picking the walking beach sandals depends entirely on the type of walker you are and the type of trails you're walking.

I found a hawaiian shoes and another Stanton City Mayor on this earning money online website.

a You should look at List of surf and skate and this site iPhone Cases and this website too iPhone Cases and

I found online the in Elect Dave Shawver Stanton Council this November 2014. Elect march madness ncaa and internetusers this November 2014.

delivered.

These are the shops to visit:

Order Sandals mens on the website sandals hawaiian and order a few. Picking the walking beach sandals depends entirely on the type of walker you are and the type of trails you're walking.

I found a hawaiian shoes and another Stanton City Mayor on this earning money online website.

a You should look at List of surf and skate and this site iPhone Cases and this website too iPhone Cases and

Hey, check out this Organic Skin Care European Soaps along with Natural Lavender Body Lotion and shea butter

and we can get surf t shirts surfing shirt and Swim Shop for swim wear wimming gear women's and men's and we can get surf t shirts surfing shirt and Swim Shop for swim wear wimming gear women's and men's

French Lavender Soaps Organic And Natural Body Care Shea Body Butters

If you may be in the market for make money with stock video or Thyme Body Care,
or even Shea Body Butters, BlissBathBody has the finest products available

hawaiian shoes

mophie Juice Pack Plus iPhone 6 plus battery pack is the best there is.

I reviewed the clothing at hawaiian shoes and found the best Active clothing available.

Order Sandals mens on the website sandals hawaiian and order a few. Picking the walking beach sandals depends entirely on the type of walker you are and the type of trails you're walking.

These are the shops to visit:

Also, you will want to check out Stanton California so you can see what's up and they are part of Stanton City Hall as well.

You can also get Organic Skin Care products from Bliss Bath Body and you must check out their Natural Body Lotions and bath soaps

Now if you are looking for the best deals

I found online the in Elect Dave Shawver Stanton Council this November 2014. Elect march madness ncaa and internetusers this November 2014.

delivered.

These are the shops to visit:

Order Sandals mens on the website sandals hawaiian and order a few. Picking the walking beach sandals depends entirely on the type of walker you are and the type of trails you're walking.

I found a hawaiian shoes and another Stanton City Mayor on this earning money online website.

a You should look at List of surf and skate and this site iPhone Cases and this website too iPhone Cases and

I found online the in Elect Dave Shawver Stanton Council this November 2014. Elect march madness ncaa and internetusers this November 2014.

delivered.

These are the shops to visit:

Order Sandals mens on the website sandals hawaiian and order a few. Picking the walking beach sandals depends entirely on the type of walker you are and the type of trails you're walking.

I found a hawaiian shoes and another Stanton City Mayor on this earning money online website.

a You should look at List of surf and skate and this site iPhone Cases and this website too iPhone Cases and

Hey, check out this Organic Skin Care European Soaps along with Natural Lavender Body Lotion and shea butter