A Javascript REPL using PyQt's QtScript

jrepl.py

#!/usr/bin/python3

import sys

from PyQt4 import QtGui
from PyQt4 import QtCore
from PyQt4 import QtScript
from PyQt4.QtScript import QScriptEngine, QScriptValue

def my_exit(context, eng):
    exit(0)

show_val = None

def my_print(context, eng):
    if context.argumentCount() == 0:
        print("")
    else:
        
        na = context.argumentCount()
        args = list()
        for i in range(na):
            args.append( str(context.argument(i).toVariant()))
        pval = ' '.join(args)
        global show_val
        print(pval)
        show_val(pval)
        
    return QScriptValue("Okay")

class JsRepl(QtGui.QMainWindow):
    def __init__(self, parent=None):
        super(JsRepl, self).__init__(parent)
        self.setWindowTitle("Javascript REPL")
        self.resize(800, 800)

        self.se = QScriptEngine()
        self.add_custom_functions()
        self.historyIndex = -1
        self.history = list()

        global show_val
        show_val = lambda x: self.results.append(x)

        self.central = QtGui.QWidget()
        lay = QtGui.QVBoxLayout()
        self.results = QtGui.QTextEdit('')
        self.results.setReadOnly(True)
        self.inputField = QtGui.QLineEdit('')
        self.inputField.editingFinished.connect(self.eval_script)
        self.inputField.installEventFilter(self)
        lay.addWidget(self.results)
        lay.addWidget(self.inputField)
        self.central.setLayout(lay)
        self.setCentralWidget(self.central)
        self.show()

        self.inputField.setFocus(True)

    def add_custom_functions(self):
        # Add exit function
        exf = self.se.newFunction(my_exit)
        self.se.globalObject().setProperty('exit', exf)

        prf = self.se.newFunction(my_print)
        self.se.globalObject().setProperty('print', prf)

    def eval_script(self):
        js = self.inputField.text()
        if len(js)==0:
            return

        self.history.append(js)
        self.historyIndex = len(self.history)
        self.results.append(js)
        res = self.se.evaluate(js)
        self.inputField.setText('')

        if res.isValid():
            if res.isFunction():
                self.results.append('    Function')
            else:
                self.results.append('    ' + str(res.toVariant()))
        else:
            self.results.append('    Error')

    def prev_cmd(self):
        if len(self.history)==0:
            return

        self.historyIndex -= 1
        if self.historyIndex >= 0:
            self.inputField.setText(self.history[self.historyIndex])
        else:
            self.inputField.setText(self.history[0])
            self.historyIndex = 0

    def next_cmd(self):
        if len(self.history)==0:
            return
        self.historyIndex += 1
        if self.historyIndex < len(self.history):
            self.inputField.setText(self.history[self.historyIndex])
        else:
            self.inputField.setText('')
            self.historyIndex = len(self.history)

    def eventFilter(self, obj, event):
        if self.inputField == obj:
            if event.type() == QtCore.QEvent.KeyPress and event.key() in{ QtCore.Qt.Key_Up,QtCore.Qt.Key_Down}:
                if event.key() == QtCore.Qt.Key_Up:
                    self.prev_cmd()
                elif event.key() == QtCore.Qt.Key_Down:
                    self.next_cmd()
                else:
                    self.historyIndex = len(self.history)-1
                return True
            else:
                return False
        return False

def main(args):
    app = QtGui.QApplication([])
    tv = JsRepl()

    sys.exit(app.exec_())

if __name__ == '__main__':
    main(sys.argv[1:])