Currency Converter GUI

# -*- coding: utf-8 -*-
"""
Created on Sun Apr 17 11:45:45 2016

@author: Blake Anderson
"""

from PySide import QtGui
from PySide import QtCore
import requests
import sys


class MainWindow(QtGui.QWidget):
    
    def __init__(self):
        super(MainWindow, self).__init__()
        response = requests.get('http://api.fixer.io/latest?base=USD')
        self.currencyDict = response.json()['rates']
        self.currencyDict['USD']=1.0        
        self.initUI()
        
    def initUI(self):
        
        self.setGeometry(300, 300, 250, 150)
        self.setWindowTitle('Currency Converter')
        self.mainLayout = QtGui.QVBoxLayout()
        self.inputValueLabel = QtGui.QLabel("Starting Amount:")
        self.inputValueField = QtGui.QDoubleSpinBox()
        
        self.inputCurrencyLabel = QtGui.QLabel("Input Currency:")
        self.outputCurrencyLabel = QtGui.QLabel("Output Currency:")        
        self.inputCurrency = QtGui.QComboBox()
        self.outputCurrency = QtGui.QComboBox()
        for currency in self.currencyDict.keys():
            self.inputCurrency.addItem(currency)
            self.outputCurrency.addItem(currency)
        
        self.calculateButton = QtGui.QPushButton("Calculate!")
        self.calculateButton.clicked.connect(self.calculate_operation)
        
        self.mainLayout.addWidget(self.inputValueLabel)
        self.mainLayout.addWidget(self.inputValueField)
        self.mainLayout.addWidget(self.inputCurrencyLabel)
        self.mainLayout.addWidget(self.inputCurrency)
        self.mainLayout.addWidget(self.outputCurrencyLabel)
        self.mainLayout.addWidget(self.outputCurrency)
        self.mainLayout.addWidget(self.calculateButton)  
        
        self.setLayout(self.mainLayout)
    
        self.show()
    
    def calculate_operation(self):
        try:
            startingCurrency = self.inputCurrency.currentText()
            targetCurrency = self.outputCurrency.currentText()
            startingAmount = float(self.inputValueField.text())
            
            valUSD = startingAmount if startingCurrency == "USD" else startingAmount / self.currencyDict[startingCurrency]
            finalValue = valUSD * self.currencyDict[targetCurrency]
            
            QtGui.QMessageBox.information(self,"Calculation Result",str(startingAmount)+" "+startingCurrency+" is equal to "+str(round(finalValue,2))+" "+targetCurrency)
        except Exception as e:
            QtGui.QMessageBox.warning(self,"Error","Not all fields contain acceptable values\nError: "+str(e))        
        

if __name__ == '__main__':
    app = QtGui.QApplication(sys.argv)
    ex = MainWindow()
    sys.exit(app.exec_())