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

#include <python_streambuf.h>

Inheritance diagram for boost_adaptbx::python::streambuf:

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.

	streambuf (bp::object &python_file_obj, char mode, std::size_t buffer_size_=0)
	constructor to enforce a mode (binary or text)

	~streambuf () override
	Mundane destructor freeing the allocated resources.

std::streamsize	showmanyc () override
	C.f. C++ standard section 27.5.2.4.3.

int_type	underflow () override
	C.f. C++ standard section 27.5.2.4.3.

int_type	overflow (int_type c=traits_type_eof()) override
	C.f. C++ standard section 27.5.2.4.5.

int	sync () override
	Update the python file to reflect the state of this stream buffer.

pos_type	seekoff (off_type off, std::ios_base::seekdir way, std::ios_base::openmode which=std::ios_base::in\|std::ios_base::out) override
	C.f. C++ standard section 27.5.2.4.2.

pos_type	seekpos (pos_type sp, std::ios_base::openmode which=std::ios_base::in\|std::ios_base::out) override
	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);

boost_adaptbx::python::streambuf::istream
Definition python_streambuf.h:510

boost_adaptbx::python::streambuf
A stream buffer getting data from and putting data into a Python file object.
Definition python_streambuf.h:111

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))

boost
Definition RDLog.h:25

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 111 of file python_streambuf.h.

Member Typedef Documentation

◆ char_type

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

Definition at line 120 of file python_streambuf.h.

◆ int_type

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

Definition at line 121 of file python_streambuf.h.

◆ off_type

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

Definition at line 123 of file python_streambuf.h.

◆ pos_type

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

Definition at line 122 of file python_streambuf.h.

◆ traits_type

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

Definition at line 124 of file python_streambuf.h.

Constructor & Destructor Documentation

◆ streambuf() [1/2]

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 138 of file python_streambuf.h.

References TEST_ASSERT.

◆ streambuf() [2/2]

boost_adaptbx::python::streambuf::streambuf	(	bp::object &	python_file_obj,
		char	mode,
		std::size_t	buffer_size_ = `0`
	)

inline

constructor to enforce a mode (binary or text)

yeah, is redundant, but it is somehow natural to do "s"

Definition at line 192 of file python_streambuf.h.

References CHECK_INVARIANT.

◆ ~streambuf()

boost_adaptbx::python::streambuf::~streambuf ( )

inlineoverride

Mundane destructor freeing the allocated resources.

Definition at line 236 of file python_streambuf.h.

Member Function Documentation

◆ overflow()

int_type boost_adaptbx::python::streambuf::overflow ( int_type c = traits_type_eof() )

inlineoverride

C.f. C++ standard section 27.5.2.4.5.

Definition at line 283 of file python_streambuf.h.

Referenced by seekoff(), and sync().

◆ seekoff()

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`
	)

inlineoverride

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 366 of file python_streambuf.h.

References overflow(), and underflow().

Referenced by seekpos().

◆ seekpos()

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

inlineoverride

C.f. C++ standard section 27.5.2.4.2.

Definition at line 429 of file python_streambuf.h.

References seekoff().

◆ showmanyc()

std::streamsize boost_adaptbx::python::streambuf::showmanyc ( )

inlineoverride

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 246 of file python_streambuf.h.

References underflow().

◆ sync()

int boost_adaptbx::python::streambuf::sync ( )

inlineoverride

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 339 of file python_streambuf.h.

References overflow().

◆ traits_type_eof()

static int boost_adaptbx::python::streambuf::traits_type_eof ( )

inlinestatic

Definition at line 127 of file python_streambuf.h.

◆ underflow()

int_type boost_adaptbx::python::streambuf::underflow ( )

inlineoverride

C.f. C++ standard section 27.5.2.4.3.

Definition at line 256 of file python_streambuf.h.

Referenced by seekoff(), and showmanyc().

Member Data Documentation

◆ default_buffer_size

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 133 of file python_streambuf.h.

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

python_streambuf.h

Classes

Public Types

Public Member Functions

Static Public Member Functions

Static Public Attributes

Detailed Description

Member Typedef Documentation

◆ char_type

◆ int_type

◆ off_type

◆ pos_type

◆ traits_type

Constructor & Destructor Documentation

◆ streambuf() [1/2]

◆ streambuf() [2/2]

◆ ~streambuf()

Member Function Documentation

◆ overflow()

◆ seekoff()

◆ seekpos()

◆ showmanyc()

◆ sync()

◆ traits_type_eof()

◆ underflow()

Member Data Documentation

◆ default_buffer_size