Just pass regular Python code as the argument to the flag:

python -c 'print 1
print 2'

Import modules works, and blank lines are OK, too:

python -c '
import pprint
pprint.pprint(1)
'

When using this feature, just be mindful of shell quoting (and indentation), and keep in mind that if you're using this outside of a few shell scripts, you might be doing it wrong.

I recommend the approaches detailed here. It starts by explaining how to execute strings of Python code, then from there details how to set up a Python environment to interact with your C program, call Python functions from your C code, manipulate Python objects from your C code, etc.

EDIT: If you really want to go the route of IPC, then you'll want to use the struct module or better yet, protlib. Most communication between a Python and C process revolves around passing structs back and forth, either over a socket or through shared memory.

I recommend creating a Command struct with fields and codes to represent commands and their arguments. I can't give much more specific advice without knowing more about what you want to accomplish, but in general I recommend the protlib library, since it's what I use to communicate between C and Python programs (disclaimer: I am the author of protlib).

I want to invoke those C function or executables in python. Is that possible.

Yes, you can write C code that can be imported into Python as a module. Python calls these extension modules. You can invoke it from Python directly, an example from the documentation:

Python Code

import example
result = example.do_something()

C Code

static PyObject * example(PyObject *self)
{
    // do something
    return Py_BuildValue("i", result);
}

If I want the C code to be a library, which means I use it with #include and linkage of the *.o likely in python, how to do it or is that possible.

You build it as a shared library *.dll or *.so You can also investigate using distutils to distribute your module.

If I write the C code into executable, which means it becomes a command, can I invoke it in python directly?

If you write a *.exe then you are doing the opposite (invoking Python from C). The method you choose (exe vs shared library) depends on if you want a "C program with some Python" or a "Python program with some C".

Also, I heard that python code can be compiled, does that mean we can execute the code without the source file? Are the output files binary files? Does it improve performance?

Python reads *.py files and compiles to *.pyc bytecode files when you run it. The bytecode is then run in the Python virtual machine. This means "executing the same file is faster the second time as recompilation from source to bytecode can be avoided." (from the Python glossary) So if you haven't edited your *.py files, it will run the *.pyc. You can distribute *.pyc files without *.py files, however they are not encrypted and can be reverse-engineered.

From everything I've seen, it's a combination of practical and historical reasons. The (mostly) historical reason is that CPython 1.0 was released in 1989. At that time, C was just recently standardized. C++ was almost unknown and decidedly non-portable, because almost nobody had a C++ compiler.

Although C++ is much more widespread and easily available today, it would still take a fair amount of work to rewrite CPython into the subset of C that's compatible with C++. By itself, that work would provide little or no real benefit.

It's a bit like Joel's blog post about starting over and doing a complete rewrite being the worst mistake a software company can make. I'd counter that by pointing to Microsoft's conversion from the Windows 3.0 core to the Windows NT core, and Apple's conversion from MacOS 9 to Mac OS/X. Neither one killed the company -- but both were definitely large, expensive, long-term projects. Both also point to something that's crucial to success: maintaining both code bases for long enough that (most) users can switch to the new code base at their leisure, based on (at least perceived) benefits.

For a development team the size of Python's, however, that kind of change is much more difficult. Even the change from Python 2 to 3 has taken quite a bit of work, and required a similar overlap. At least in that case, however, there are direct benefits to the changes, which rewriting into C++ (by itself) wouldn't (at least immediately) provide.

Linus Torvalds's rant against C++ was brought up, so I'll mention that as well. Nothing I've seen from Guido indicates that he has that sort of strong, negative feelings toward C++. About the worst I've seen him say is that teaching C++ is often a disaster -- but he immediately went on to say that this is largely because the teachers didn't/don't know C++.

I also think that while it's possible to convert a lot of C code to C++ with relative ease, that getting much real advantage from C++ requires not only quite a bit more rewriting than that, but also requires substantial re-education of most developers involved. Most well-written C++ is substantially different from well-written C to do the same things. It's not just a matter of changing malloc to new and printf to cout, by any stretch of the imagination.