list - How do I create an error message using pickAFile() in Jython? -

i creating program various calculations list of numbers.

how can show error message if presses "cancel" while choosing file pickafile()? when cancel it, error message for line in file line.

the error message is:

>"the error was:stream closed > i/o operation failed. >  > tried read file, , couldn't.  sure file exists? > if exist, did specify correct directory/folder?" 

here's code:

def selectfilecalculatestatistics():    fullpathname = pickafile()   file = open(fullpathname, "r")    listnumbers = readlistnumbers(file)    min = calculateminimum(listnumbers)    max = calculatemaximum(listnumbers)    mean = calculatemean(listnumbers)    standarddeviation = calculatestandarddeviation(listnumbers, mean)    print("the minimum number list is: " + str(min))   print("the maximum number list is: \n" + str(max))   print("the mean number list is: " + str(round(mean, 2)))   print("the standard deviation list is: " + str(round(standarddeviation, 2)))    file.close()   def readlistnumbers(fullpathname):        file = open(fullpathname, "r")       listnumbers = []        line in file:         listnumbers.append(float(line.rstrip('\n')))        return listnumbers 

while pickafile() returns none if user pressed cancel button can raise exception:

fullpathname = pickafile() if not fullpathname:     raise ioerror('cancel pressed')