在python中显示sympy渲染svg时出现问题 [英] problem displaying sympy rendered svg in python

问题描述

我有以下程序，该程序使用sympy和svgmath来呈现用户的代数表达式.几乎可以使用，但是存在一些问题:

I have the following program which uses sympy and svgmath to render a user's algebraic expression. It nearly works but there are a few issues:

1. 在程序退出之前实际上不会产生svg，因此显然无法显示.
2. 是否有一种提高性能的方法(不是每次都查找'svgmath.xml'?)
3. 是否需要生成实际的svg文件? svgmath可以将输出直接传递到QSvgWidget吗?

非常感谢和最良好的祝愿.

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_()

推荐答案

您应该关闭文件句柄，因为否则写入的数据可能尚未刷新到文件系统中.

You should close the file handles, because otherwise the data written may not yet have been flushed to the filesystem.

parser.parse()
output.close()

或者，使用with表达式.

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

是否需要生成实际的svg文件?

Does an actual svg file need to be produced?

我认为QSvgWidget提供了一个load插槽，该插槽需要包含文件内容的字节字符串.

I think QSvgWidget offers a load slot, which takes a byte string with the file contents.

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