Python 大小写转换

def low_UPER():
oldNme='demo.txt'
newName='my.txt'
fp = open(oldNme,"r+")
newFp = open(newName,"w")
for eachline in fp.readlines():
newStr = eachline.replace(" ","").replace("\t","").strip()

        #print "Write:",newStr
        newFp.write(newStr.upper())
    fp.close()
    newFp.close()
    #
    doc=os.getcwd()
    mytree=os.listdir(doc)
    print mytree
    for i in mytree:
        if i == oldNme:
           mytree.remove(i)
    os.rename(newName,oldNme)