Computer Science 15-110, Spring 2011
Class Notes:  File IO


# File Input/Output in Python

import os

def getDesktopPath(filename = ""):
    # next line is odd, but works in Windows/Mac/Linux
    homepath = os.getenv('USERPROFILE') or os.getenv('HOME')
    return homepath + os.sep + "Desktop" + os.sep + filename

def fileExists(filename):
    return os.path.exists(filename)
   
def deleteFile(filename):
    if (fileExists(filename) == True):
        os.remove(filename)

def readTextFile(filename):
    if (fileExists(filename) == False):
        print "File does not exist:", filename
        return None
    fileHandler = open(filename, "rt")
    text = fileHandler.read()
    fileHandler.close()
    return text

def readTextFileAsList(filename):
    # readlines includes '\n' characters, so we'll use split() instead
    text = readTextFile(filename)
    if (text == None):
        return None
    return text.split("\n")

def writeTextFile(text, filename):
    fileHandler = open(filename, "wt")
    fileHandler.write(text)
    fileHandler.close()

def testFileIO():
    print "Testing File IO..."
    filename = getDesktopPath("test.txt")
    deleteFile(filename)
    assert(fileExists(filename) == False)
    print "Reading from a non-existent file (error message expected)..."
    text = readTextFile(filename)
    assert(text == None)
    text = "This is a test.\nIt is only a test."
    writeTextFile(text, filename)
    assert(fileExists(filename) == True)
    text = readTextFile(filename)
    assert(text == "This is a test.\nIt is only a test.")
    textList = readTextFileAsList(filename)
    assert(textList == ["This is a test.", "It is only a test."])
    assert(fileExists(filename) == True)
    #deleteFile(filename)
    #assert(fileExists(filename) == False)
    print "Passed!"

testFileIO()