问题
I have been working on a project that pipes data back and forth between a QGIS plugin written in Python and some image processing code I have written in C++. After some community help via the following 2 questions I have gotten a console based sample code working that simulates an image, pipes it over to my C++ code, does some nontrivial processing, and then pipes it back and unpacks it correctly. I am having trouble porting this to a GUI style code.
previous questions for reference:
Data corruption Piping between C++ and Python
piping binary data between python and c++
The current (and I firmly believe last) hurdle left is that when I move from a PyDev environment to my QGIS plugin (which is GUI based) my ability to place stdin and stdout in Binary mode raises an error.
my working Python code that I run from PyDev is:
import subprocess
import struct
import sys
import os, msvcrt
msvcrt.setmode(sys.stdout.fileno(), os.O_BINARY)
msvcrt.setmode(sys.stdin.fileno(), os.O_BINARY)
import numpy as np
import datetime
#set up the variables needed
bytesPerDouble = 8
sizeX = 2000
sizeY = 2000
offset = sizeX*sizeY
totalBytesPerArray = sizeX*sizeY*bytesPerDouble
totalBytes = totalBytesPerArray*2 #the 2 is because we pass 2 different versions of the 2D array
#setup the testing data array
a = np.zeros(sizeX*sizeY*2, dtype='d')
for i in range(sizeX):
for j in range(sizeY):
a[j+i*sizeY] = i
a[j+i*sizeY+offset] = i
if i % 10 == 0:
a[j+i*sizeY+offset] = j
data = a.tobytes('C')
strTotalBytes = str(totalBytes)
strLineBytes = str(sizeY*bytesPerDouble)
#communicate with c++ code
print("starting C++ code")
command = "C:\Python27\PythonPipes.exe"
proc = subprocess.Popen([command, strTotalBytes, strLineBytes, str(sizeY), str(sizeX)], stdin=subprocess.PIPE,stderr=subprocess.PIPE,stdout=subprocess.PIPE)
ByteBuffer = (data)
proc.stdin.write(ByteBuffer)
starttime = datetime.datetime.now()
print("Getting Status from C++")
for i in range(sizeX-6):
returnvalues = proc.stdout.read(4)
a = buffer(returnvalues)
b = struct.unpack_from('i', a)
currenttime = datetime.datetime.now()
deltatime = (currenttime-starttime).total_seconds()
print "ETA for processing completion " + str( ((sizeX + 0.0) / (b[0] + 0.0) - 1.0)*deltatime) + " Seconds"
print("Reading results back from C++")
for i in range(sizeX):
returnvalues = proc.stdout.read(sizeY*bytesPerDouble)
a = buffer(returnvalues)
b = struct.unpack_from(str(sizeY)+'d', a)
print str(b) + " " + str(i)
print('done')
when I move this code over to my QGIS module (which is built with Plugin Builder and QtCreator) using this code:
import resources
from qgis.core import *
import qgis.utils
import time
import struct
import subprocess
import os, msvcrt
import sys
msvcrt.setmode(sys.stdout.fileno(), os.O_BINARY)
msvcrt.setmode(sys.stdin.fileno(), os.O_BINARY)
import datetime
class CreateRasterLayer:
def __init__(self, ex_iface):
self.iface = ex_iface
def setupImageSpacing(self):
#grab the layers in QGIS
layers = self.iface.legendInterface().layers()
#grab "gsd" per pixel
self.deltaX = (layers[0].extent().xMaximum() -layers[0].extent().xMinimum())/layers[0].width()
self.deltaY = (layers[0].extent().yMaximum() -layers[0].extent().yMinimum())/layers[0].height()
#get overlap of layers
self.AOI = layers[0].extent().intersect(layers[1].extent())
self.width = int((self.AOI.xMaximum() - self.AOI.xMinimum()) // self.deltaX)
self.height = int((self.AOI.yMaximum() - self.AOI.yMinimum()) // self.deltaY)
print(self.AOI.asWktCoordinates())
print(self.width)
print(self.height)
entropyRadius = 7
self.CalculateEntropy(layers, entropyRadius)
def CalculateEntropy(self, layers, radius):
#variables used in this Python Script
bytesPerNumber = 8 # Python uses 8 bytes for all floating point numbers
bytesPerColumn = self.height*bytesPerNumber # This is the number of bytes in one column of data. data will be passed to c++ program 1 column at a time over pipes
bytesPerLayer = self.width* bytesPerColumn # This is the number of bytes in one of the layers that is going to e sent to the c++ program
RedBytes = bytearray(bytesPerLayer*2) # Byte array that will be passed to the C++ array. this holds the Red channel data for the layer for testing purposes.
#arguments that will be passed to the c++ program
strTotalBytes = str(bytesPerLayer*2) #number of bytes that will be passed to the C++ program total
strLineBytes = str(bytesPerColumn) #number of bytes that will be passed to the C++ program at a time
strHeight = str(self.height) #number of doubles that are being passed to the C++ program at a time
strWidth = str(self.width) #number of data data passes to the C++ program need to completely transfer one layer object
#start the C++ program
print("starting C++ code for processing layers")
command = ["C:\Python27\PythonPipes.exe", strTotalBytes , strLineBytes , strHeight, strWidth]
proc = subprocess.Popen( command, stdin=subprocess.PIPE,stdout=subprocess.PIPE,stderr=subprocess.PIPE)
print("Piping layer 1 -> C++")
print(time.ctime(time.time()))
currentlayer = 0
value = bytearray(bytesPerColumn)
#read the data in the first layer
for i in range(self.width):
for j in range(self.height):
#calculate the index of the byte array where this data should be placed
currentindex = bytesPerLayer*currentlayer + (j+i*self.height)*bytesPerNumber
#retrieve the value of the pixel at the current raster layer location
pixelData0 = layers[0].dataProvider().identify(QgsPoint(self.AOI.xMinimum()+i*self.deltaX, self.AOI.yMinimum()+j*self.deltaY),QgsRaster.IdentifyFormatValue)
#convert the pixel data for the Red Channel into it's 'C' byte ordering and assign it to the RedByte Array
RedBytes[ currentindex: currentindex + bytesPerNumber] = struct.pack('d',pixelData0.results()[1])
#copy bytes into the Buffer for piping
RedBuffer = buffer(RedBytes, bytesPerLayer*currentlayer + (i*self.height)*bytesPerNumber, bytesPerColumn)
#pipe the data for the whole column over to the C++ program
proc.stdin.write(RedBuffer)
print("Piping layer 2 -> C++")
print(time.ctime(time.time()))
currentlayer += 1
#comments the same as the previous loops
for i in range(self.width):
for j in range(self.height):
currentindex = bytesPerLayer*currentlayer + (j+i*self.height)*bytesPerNumber
pixelData1 = layers[1].dataProvider().identify(QgsPoint(self.AOI.xMinimum()+i*self.deltaX, self.AOI.yMinimum()+j*self.deltaY),QgsRaster.IdentifyFormatValue)
RedBytes[ currentindex: currentindex + bytesPerNumber] = struct.pack('d',pixelData1.results()[1])
RedBuffer = buffer(RedBytes, bytesPerLayer*currentlayer + (i*self.height)*bytesPerNumber, bytesPerColumn)
proc.stdin.write(RedBuffer)
print("Data piped")
print(time.ctime(time.time()))
starttime = datetime.datetime.now()
print("Getting Status from C++")
for i in range(self.width-6):
returnvalues = proc.stdout.read(4)
a = buffer(returnvalues)
b = struct.unpack_from('i', a)
currenttime = datetime.datetime.now()
deltatime = (currenttime-starttime).total_seconds()
print "ETA for processing completion " + str( ((self.width + 0.0) / (b[0] + 0.0) - 1.0)*deltatime) + " Seconds"
#receive the data and process it here
print("Reading results back from C++")
for i in range(self.width):
returnvalues = proc.stdout.read(bytesPerColumn)
a = buffer(returnvalues)
b = struct.unpack_from(str(self.height)+'d', a)
print str(b) + " " + str(i)
I get the following error message:
msvcrt.setmode(sys.stdout.fileno(), os.O_BINARY) AttributeError: writeOut instance has no attribute 'fileno'
The last time I had a stdin/stdout error with this project the problem was with the popen statement. popen required that I pipe all three std streams when I called it from a GUI code. Since this is related to the std streams and the code works in PyDev on the console I am assuming that it is a GUI code related problem right now.
I would like to know the proper way to set std streams to binary mode from a GUI code, or any other ideas that could resolve the error issue.
Update I found a work around, but will leave the question open in case someone has a real fix. I have found a work around for this problem. I just removed the code that was trying to set std streams to binary mode from python and left them in my C++ code as the first thing that happens. When the python code calls the popen line, the C++ process sets the std streams to binary mode for me. I would still like to know if Python has a way to get around this error
来源：https://stackoverflow.com/questions/37007900/piping-binary-data-from-python-gui-to-c-and-back-again