PythonCalulator (GUI example)

A Calculator

# [Create a window]

import sys
from PyQt4.QtCore import *
from PyQt4.QtGui import *
from math import *


class Window(QWidget):
	"""Main window handling
	"""
	def __init__(self, parent = None):
		"""Constructor
		@param parent: the window parent or <i>none</i>
		"""
		QWidget.__init__(self, parent) 
		self.setWindowTitle(self.tr("Calculator"))
		self._labelFormula = QLabel(self.tr("Formula:"))
		self._editFormula = QLineEdit()
		self._editFormula.setToolTip(self.tr("Any mathematical formula like '2.777+sin(3.14/3)+log(1.99e+7)'"))
		self._labelResult = QLabel(self.tr("Result:"))
		self._labelResult2 = QLabel("")
		self._buttonCalc = QPushButton(self.tr("Calc"))
		self._buttonCalc.default = True
		self._listHistory = QListWidget()
		

		# Put the widgets in a layout (now they start to appear):
		layout = QGridLayout(self)
		layout.addWidget(self._labelFormula, 0, 0)
		layout.addWidget(self._editFormula, 0, 1)
		layout.addWidget(self._buttonCalc, 1, 1)
		layout.addWidget(self._labelResult, 2, 0)
		layout.addWidget(self._labelResult2, 2, 1)
		# addWidget(row, col, rowspan, colspan):
		layout.addWidget(self._listHistory, 3, 0, 2, 2)
		layout.setRowStretch(4, 1)

		self.connect(self._buttonCalc, SIGNAL("clicked()"), self.onClickCalc)

	def onClickCalc(self):
		"""Event handler for the button click
		"""
		try:
			text = str(self._editFormula.text())
			rc = str(eval(text))
			self._labelResult2.setText(rc)
			self._listHistory.addItem(text + " = " + rc)
		except Exception as e:
			self._labelResult2.setText("+++ " + repr(e))
		
    
if __name__ == "__main__":
	app = QApplication(sys.argv)
	window = Window()
	# Let's resize the window:
	window.resize(480, 250)
	window.show()
	sys.exit(app.exec_())