A stream buffer getting data from and putting data into a Python file object. More...

#include <python_streambuf.h>

Classes
class	istream
class	ostream
Public Types
typedef base_t::char_type	char_type
typedef base_t::int_type	int_type
typedef base_t::pos_type	pos_type
typedef base_t::off_type	off_type
typedef base_t::traits_type	traits_type
Public Member Functions
	streambuf (bp::object &python_file_obj, std::size_t buffer_size_=0)
	Construct from a Python file object.
virtual	~streambuf ()
	Mundane destructor freeing the allocated resources.
virtual std::streamsize	showmanyc ()
	C.f. C++ standard section 27.5.2.4.3.
virtual int_type	underflow ()
	C.f. C++ standard section 27.5.2.4.3.
virtual int_type	overflow (int_type c=traits_type_eof())
	C.f. C++ standard section 27.5.2.4.5.
virtual int	sync ()
	Update the python file to reflect the state of this stream buffer.
virtual pos_type	seekoff (off_type off, std::ios_base::seekdir way, std::ios_base::openmode which=std::ios_base::in\|std::ios_base::out)
	C.f. C++ standard section 27.5.2.4.2.
virtual pos_type	seekpos (pos_type sp, std::ios_base::openmode which=std::ios_base::in\|std::ios_base::out)
	C.f. C++ standard section 27.5.2.4.2.
Static Public Member Functions
static int	traits_type_eof ()
Static Public Attributes
static const std::size_t	default_buffer_size = 1024
	The default size of the read and write buffer.

Detailed Description

A stream buffer getting data from and putting data into a Python file object.

The aims are as follow:

Given a C++ function acting on a standard stream, e.g.

      void read_inputs(std::istream& input) {
        ...
        input >> something >> something_else;
      }

and given a piece of Python code which creates a file-like object, to be able to pass this file object to that C++ function, e.g.

      import gzip
      gzip_file_obj = gzip.GzipFile(...)
      read_inputs(gzip_file_obj)

and have the standard stream pull data from and put data into the Python file object.

When Python read_inputs() returns, the Python object is able to continue reading or writing where the C++ code left off.

Operations in C++ on mere files should be competitively fast compared to the direct use of std::fstream.

Motivation

the standard Python library offer of file-like objects (files, compressed files and archives, network, ...) is far superior to the offer of streams in the C++ standard library and Boost C++ libraries.

i/o code involves a fair amount of text processing which is more efficiently prototyped in Python but then one may need to rewrite a time-critical part in C++, in as seamless a manner as possible.

Usage

This is 2-step:

a trivial wrapper function

          using boost_adaptbx::python::streambuf;
          void read_inputs_wrapper(streambuf& input)
          {
            streambuf::istream is(input);
            read_inputs(is);
          }

          def("read_inputs", read_inputs_wrapper);

which has to be written every time one wants a Python binding for such a C++ function.

the Python side

          from boost.python import streambuf
          read_inputs(streambuf(python_file_obj=obj, buffer_size=1024))

buffer_size is optional. See also: default_buffer_size

Note: references are to the C++ standard (the numbers between parentheses at the end of references are margin markers).

Definition at line 108 of file python_streambuf.h.

Member Typedef Documentation

typedef base_t::char_type boost_adaptbx::python::streambuf::char_type

Definition at line 118 of file python_streambuf.h.

typedef base_t::int_type boost_adaptbx::python::streambuf::int_type

Definition at line 119 of file python_streambuf.h.

typedef base_t::off_type boost_adaptbx::python::streambuf::off_type

Definition at line 121 of file python_streambuf.h.

typedef base_t::pos_type boost_adaptbx::python::streambuf::pos_type

Definition at line 120 of file python_streambuf.h.

typedef base_t::traits_type boost_adaptbx::python::streambuf::traits_type

Definition at line 122 of file python_streambuf.h.

Constructor & Destructor Documentation

boost_adaptbx::python::streambuf::streambuf	(	bp::object &	python_file_obj,
		std::size_t	buffer_size_ = `0`
	)			`[inline]`

Construct from a Python file object.

if buffer_size is 0 the current default_buffer_size is used.

Definition at line 137 of file python_streambuf.h.

References TEST_ASSERT.

virtual boost_adaptbx::python::streambuf::~streambuf ( ) [inline, virtual]

Mundane destructor freeing the allocated resources.

Definition at line 190 of file python_streambuf.h.

Member Function Documentation

virtual int_type boost_adaptbx::python::streambuf::overflow ( int_type c = traits_type_eof() ) [inline, virtual]

C.f. C++ standard section 27.5.2.4.5.

Definition at line 231 of file python_streambuf.h.

Referenced by seekoff(), and sync().

virtual pos_type boost_adaptbx::python::streambuf::seekoff	(	off_type	off,
		std::ios_base::seekdir	way,
		std::ios_base::openmode	which = `std::ios_base::in \| std::ios_base::out`
	)			`[inline, virtual]`

C.f. C++ standard section 27.5.2.4.2.

This implementation is optimised to look whether the position is within the buffers, so as to avoid calling Python seek or tell. It is important for many applications that the overhead of calling into Python is avoided as much as possible (e.g. parsers which may do a lot of backtracking)

Definition at line 284 of file python_streambuf.h.

References overflow(), and underflow().

Referenced by seekpos().

virtual pos_type boost_adaptbx::python::streambuf::seekpos	(	pos_type	sp,
		std::ios_base::openmode	which = `std::ios_base::in \| std::ios_base::out`
	)			`[inline, virtual]`

C.f. C++ standard section 27.5.2.4.2.

Definition at line 342 of file python_streambuf.h.

References seekoff().

virtual std::streamsize boost_adaptbx::python::streambuf::showmanyc ( ) [inline, virtual]

C.f. C++ standard section 27.5.2.4.3.

It is essential to override this virtual function for the stream member function readsome to work correctly (c.f. 27.6.1.3, alinea 30)

Definition at line 198 of file python_streambuf.h.

References underflow().

virtual int boost_adaptbx::python::streambuf::sync ( ) [inline, virtual]

Update the python file to reflect the state of this stream buffer.

Empty the write buffer into the Python file object and set the seek position of the latter accordingly (C++ standard section 27.5.2.4.2). If there is no write buffer or it is empty, but there is a non-empty read buffer, set the Python file object seek position to the seek position in that read buffer.

Definition at line 261 of file python_streambuf.h.

References overflow().

Referenced by boost_adaptbx::python::streambuf::istream::~istream().

static int boost_adaptbx::python::streambuf::traits_type_eof ( ) [inline, static]

Definition at line 126 of file python_streambuf.h.

virtual int_type boost_adaptbx::python::streambuf::underflow ( ) [inline, virtual]

C.f. C++ standard section 27.5.2.4.3.

Definition at line 206 of file python_streambuf.h.

Referenced by seekoff(), and showmanyc().

Member Data Documentation

const std::size_t boost_adaptbx::python::streambuf::default_buffer_size = 1024 [static]

The default size of the read and write buffer.

They are respectively used to buffer data read from and data written to the Python file object. It can be modified from Python.

Definition at line 132 of file python_streambuf.h.

The documentation for this class was generated from the following file:

python_streambuf.h

boost_adaptbx::python::streambuf Class Reference

Classes

Public Types

Public Member Functions

Static Public Member Functions

Static Public Attributes

Detailed Description

Member Typedef Documentation

Constructor & Destructor Documentation

Member Function Documentation

Member Data Documentation