Python Bytes Reading Example - Revision history

Iwiseman: /* Improved Version using memoryview */

2020-07-22T08:16:10Z

Improved Version using memoryview

← Older revision		Revision as of 08:16, 22 July 2020
Line 242:		Line 242:

	</syntaxhighlight>		</syntaxhighlight>
			Note the del of the following. We may need to understand why this was required.
			<syntaxhighlight lang="python">
			del vertices
			del mem
			</syntaxhighlight>
			Without this we get
			BufferError: cannot close exported pointers exist
			The memoryview object must be cleaned up prior to closing the mmap

Iwiseman: /* Improved Version using memoryview */

2020-07-22T07:55:05Z

Improved Version using memoryview

← Older revision		Revision as of 07:55, 22 July 2020
Line 130:		Line 130:

	= Improved Version using memoryview =		= Improved Version using memoryview =
			memoryview offers a better way to validate binary data and provides a cast function.

	<syntaxhighlight lang="python">		<syntaxhighlight lang="python">

Iwiseman: /* Improved Version using memoryview */

2020-07-22T07:54:15Z

Improved Version using memoryview

← Older revision		Revision as of 07:54, 22 July 2020
Line 132:		Line 132:

	<syntaxhighlight lang="python">		<syntaxhighlight lang="python">
			"""Read binary file produced by colorpoints.c in Python.

			Demonstrate use of the struct module
			"""
			import code

			import mmap
			from pprint import pprint as pp
			from binascii import hexlify


			class Vector:

			def __init__(self, mem_float32):
			if mem_float32.format not in "fd":
			raise TypeError("Vector: memoryview values must be floating-point numbers")
			if len(mem_float32) < 3:
			raise TypeError("Vector: memoryview must contain at least 3 floats")
			self._mem = mem_float32

			@property
			def x(self):
			return self._mem[0]

			@property
			def y(self):
			return self._mem[1]

			@property
			def z(self):
			return self._mem[2]

			def __repr__(self):
			return 'Vector({}, {}, {})'.format(self.x, self.y, self.z)


			class Color:

			def __init__(self, mem_uint16):
			if mem_uint16.format not in "HILQ":
			raise TypeError("Color: memoryview values must be unsigned integers")
			if len(mem_uint16) < 3:
			raise TypeError("Color: memoryview must contain at least 3 integers")
			self._mem = mem_uint16

			@property
			def red(self):
			return self._mem[0]

			@property
			def green(self):
			return self._mem[1]

			@property
			def blue(self):
			return self._mem[2]

			def __repr__(self):
			return 'Color({}, {}, {})'.format(self.red, self.green, self.blue)


			class Vertex:

			def __init__(self, vector, color):
			self.vector = vector
			self.color = color

			def __repr__(self):
			return 'Vertex({!r}, {!r})'.format(self.vector, self.color)


			def make_colored_vertex(mem_vertex):
			mem_vector = mem_vertex[0:12].cast('f')
			mem_color = mem_vertex[12:18].cast('H')
			return Vertex(Vector(mem_vector),
			Color(mem_color))


			def main():
			with open('colors.bin', 'rb') as f:
			with mmap.mmap(f.fileno(), 0, access=mmap.ACCESS_READ) as buffer:

			print("buffer: {} bytes".format(len(buffer)))

			indexes = ' '.join(str(n).zfill(2) for n in range(len(buffer)))
			print(indexes)

			hex_buffer = hexlify(buffer).decode('ascii')
			hex_pairs = ' '.join(hex_buffer[i:i+2] for i in range(0, len(hex_buffer), 2))
			print(hex_pairs)

			mem = memoryview(buffer)

			VERTEX_SIZE = 18
			VERTEX_STRIDE = VERTEX_SIZE + 2

			vertex_mems = (mem[i:i + VERTEX_SIZE] for i in range(0, len(mem), VERTEX_STRIDE))
			vertices = [make_colored_vertex(vertex_mem) for vertex_mem in vertex_mems]

			pp(vertices)

			del vertices
			del mem


			if __name__ == '__main__':
			main()

	</syntaxhighlight>		</syntaxhighlight>

Iwiseman: /* Python Program */

2020-07-22T07:53:31Z

Python Program

← Older revision		Revision as of 07:53, 22 July 2020
Line 127:		Line 127:
	if __name__ == '__main__':		if __name__ == '__main__':
	main()		main()
			</syntaxhighlight>

			= Improved Version using memoryview =

			<syntaxhighlight lang="python">
	</syntaxhighlight>		</syntaxhighlight>

Iwiseman: /* Python Program */

2020-07-22T07:39:15Z

Python Program

← Older revision		Revision as of 07:39, 22 July 2020
Line 62:		Line 62:
	[[File:Format_chars_struct.png\|upright=0.25]]		[[File:Format_chars_struct.png\|upright=0.25]]

			This also demonstrates the outputting of bytes using python.
	<syntaxhighlight lang="python">		<syntaxhighlight lang="python">
	import struct		import struct

Iwiseman: /* Python Program */

2020-07-22T07:38:28Z

Python Program

← Older revision		Revision as of 07:38, 22 July 2020
Line 60:		Line 60:
	Which allows the program to read types, in this case fffhhh into a buffer. The xx represents the packing which is required due to the use of the compiler at the time. This may vary.		Which allows the program to read types, in this case fffhhh into a buffer. The xx represents the packing which is required due to the use of the compiler at the time. This may vary.

	[[File:Format_chars_struct.png\|upright=0.5]]		[[File:Format_chars_struct.png\|upright=0.25]]

	<syntaxhighlight lang="python">		<syntaxhighlight lang="python">

Iwiseman: /* Python Program */

2020-07-22T07:38:07Z

Python Program

← Older revision		Revision as of 07:38, 22 July 2020
Line 59:		Line 59:
	struct.iter_unpack('@3f3Hxx', buffer)		struct.iter_unpack('@3f3Hxx', buffer)
	Which allows the program to read types, in this case fffhhh into a buffer. The xx represents the packing which is required due to the use of the compiler at the time. This may vary.		Which allows the program to read types, in this case fffhhh into a buffer. The xx represents the packing which is required due to the use of the compiler at the time. This may vary.

			[[File:Format_chars_struct.png\|upright=0.5]]

	<syntaxhighlight lang="python">		<syntaxhighlight lang="python">

Iwiseman: /* Python Program */

2020-07-22T07:36:22Z

Python Program

← Older revision		Revision as of 07:36, 22 July 2020
Line 56:		Line 56:
	</syntaxhighlight>		</syntaxhighlight>
	= Python Program =		= Python Program =
			This demonstrates the use of
			struct.iter_unpack('@3f3Hxx', buffer)
			Which allows the program to read types, in this case fffhhh into a buffer. The xx represents the packing which is required due to the use of the compiler at the time. This may vary.

	<syntaxhighlight lang="python">		<syntaxhighlight lang="python">
	import struct		import struct

Iwiseman: Created page with "= C Program = This generates a binary file for reading via Python /** * colorpoints.c * * A C99 program to write a colored vertex * structure..."

2020-07-22T07:32:47Z

Created page with "= C Program = This generates a binary file for reading via Python <syntaxhighlight lang="c"> /** * colorpoints.c * * A C99 program to write a colored vertex * structure..."

New page

= C Program =
This generates a binary file for reading via Python
<syntaxhighlight lang="c">
/**
* colorpoints.c
*
* A C99 program to write a colored vertex
* structures to a binary file.
*
*/

#include <stdio.h>

struct Vector {
float x;
float y;
float z;
};

struct Color {
unsigned short int red;
unsigned short int green;
unsigned short int blue;
};

struct Vertex {
struct Vector position;
struct Color color;
};

int main(int argc, char** argv) {
struct Vertex vertices[] = {
{ .position = { 3323.176, 6562.231, 9351.231 },
.color = { 3040, 34423, 54321 } },

{ .position = { 7623.982, 2542.231, 9823.121 },
.color = { 32736, 5342, 2321 } },

{ .position = { 6729.862, 2347.212, 3421.322 },
.color = { 45263, 36291, 36701 } },

{ .position = { 6352.121, 3432.111, 9763.232 },
.color = { 56222, 36612, 11214 } } };

FILE* file = fopen("colors.bin", "wb");

if (file == NULL) {
return -1;
}

fwrite(vertices, sizeof(struct Vertex), 4, file);
fclose(file);

return 0;
}
</syntaxhighlight>
= Python Program =
<syntaxhighlight lang="python">
import struct
from pprint import pprint as pp
from binascii import hexlify

class Vector:

def __init__(self, x, y, z):
self.x = x
self.y = y
self.z = z

def __repr__(self):
return 'Vector({}, {}, {})'.format(self.x, self.y, self.z)

class Color:

def __init__(self, red, green, blue):
self.red = red
self.green = green
self.blue = blue

def __repr__(self):
return 'Color({}, {}, {})'.format(self.red, self.green, self.blue)

class Vertex:

def __init__(self, vector, color):
self.vector = vector
self.color = color

def __repr__(self):
return 'Vertex({!r}, {!r})'.format(self.vector, self.color)

def make_colored_vertex(x, y, z, red, green, blue):
return Vertex(Vector(x, y, z),
Color(red, green, blue))

def main():
with open('colors.bin', 'rb') as f:
buffer = f.read()

print("buffer: {} bytes".format(len(buffer)))

indexes = ' '.join(str(n).zfill(2) for n in range(len(buffer)))
print(indexes)

hex_buffer = hexlify(buffer).decode('ascii')
hex_pairs = ' '.join(hex_buffer[i:i+2] for i in range(0, len(hex_buffer), 2))
print(hex_pairs)

vertices = []
for fields in struct.iter_unpack('@3f3Hxx', buffer):
vertex = make_colored_vertex(*fields)
vertices.append(vertex)

pp(vertices)

if __name__ == '__main__':
main()
</syntaxhighlight>