python中怎样求行数？

count = len(open(filepath,'rU').readlines())

count = -1

for count, line in enumerate(open(thefilepath, 'rU')):

    pass

count += 1

count = 0

thefile = open(thefilepath, 'rb')

while True:

    buffer = thefile.read(8192*1024)

    if not buffer:

        break

    count += buffer.count('\n')

thefile.close( )