1. use with

with open("x.txt") as f:
    for line in f:
        do something with data

2. use of yield

def readInChunks(fileObj, chunkSize=2048):
    """
    Lazy function to read a file piece by piece.
    Default chunk size: 2kB.
    """
    while True:
        data = fileObj.read(chunkSize)
        if not data:
            break
        yield data

f = open('bigFile')
for chuck in readInChunks(f):
    do_something(chunk)
f.close()