Sympy rendered svg mapping issue in python

Question

I have the following program that uses sympy and svgmath to display a custom algebraic expression. It almost works, but there are a few problems:

• svg is not actually created until the program exits, so obviously it cannot be diplayed.
• Is there a way to improve performance (without looking at "svgmath.xml" every time, etc.)?
• Should the actual svg file be created? Can svgmath pass output directly to QSvgWidget?

Many thanks and best wishes.

from __future__ import division import sys import sympy from PySide.QtGui import * from PySide.QtCore import * from PySide.QtXml import * from PySide.QtSvg import * from xml import sax from xml.sax.saxutils import XMLGenerator from svgmath.tools.saxtools import XMLGenerator, ContentFilter from svgmath.mathhandler import MathHandler, MathNS from sympy.printing.mathml import mathml from sympy.abc import x from sympy.utilities.mathml import c2p import libxml2 import StringIO class Form(QDialog): def __init__(self, parent=None): super(Form, self).__init__(parent) self.browser = QTextBrowser() self.browser.setCurrentFont(QFont("Courier New",10,QFont.Bold)) self.lineedit = QLineEdit("please type an expression") self.lineedit.selectAll() self.svgwidget = QSvgWidget() layout = QVBoxLayout() layout.addWidget(self.browser) layout.addWidget(self.lineedit) layout.addWidget(self.svgwidget) self.setLayout(layout) self.lineedit.setFocus() self.connect(self.lineedit, SIGNAL("textChanged (const QString&)"),self.updateUi) def updateUi(self): text = unicode(self.lineedit.text()) for z in range(0,9): text = text.replace('x'+str(z),'x^'+str(z)) text = text.replace(')'+str(z),')^'+str(z)) text = text.replace(str(z)+'x',str(z)+'*x') text = text.replace(str(z)+'(',str(z)+'*(') try: prettytext = sympy.printing.pretty(sympy.sympify(text)) self.browser.clear() self.browser.append(prettytext) # Open all files output = open("test.svg", "w") config = open("svgmath.xml", "r") # Create the converter as a content handler. saxoutput = XMLGenerator(output, 'utf-8') handler = MathHandler(saxoutput, config) # Parse input file with a namespace-aware SAX parser parser = sax.make_parser() parser.setFeature(sax.handler.feature_namespaces, 1) parser.setContentHandler(handler) parser.parse(StringIO.StringIO(c2p(mathml(sympy.sympify(text)), simple=True))) self.svgwidget.load("test.svg") except Exception: if text=='': self.browser.clear() app = QApplication(sys.argv) form = Form() form.show() app.exec_() 

Answer 1

You must close the file descriptors, because otherwise the recorded data cannot yet be flushed to the file system.

 parser.parse() output.close() 

Alternatively, use the with statement.

 with open("test.svg", "w") as output: ... parser.parse() load() 

Do you need to create the actual svg file?

I think QSvgWidget offers a load slot that takes a byte string with the contents of the file.