1. 最基本的读文件方法：# File: readline-example-1.py file = open("sample.txt") while 1:    line = file.readline()    if not line:        break    pass # do something　　一行一行得从文件读数据，显然比较慢；不过很省内存。　　在我的机器上读10M的sample.txt文件，每秒大约读32000行2. 用fileinput模块# File: readline-example-2.py import fileinput for line in fileinput.input("sample.txt"):    pass　　写法简单一些，不过测试以后发现每秒只能读13000行数据，效率比上一种方法慢了两倍多……3. 带缓存的文件读取# File: readline-example-3.py file = open("sample.txt") while 1:    lines = file.readlines(100000)    if not lines:        break    for line in lines:        pass # do something　　这个方法真的更好吗？事实证明，用同样的数据测试，它每秒可以读96900行数据！效率是第一种方法的3倍，第二种方法的7倍！————————————————————————————————————————————————————————————　　在Python 2.2以后，我们可以直接对一个file对象使用for循环读每行数据：# File: readline-example-5.py file = open("sample.txt") for line in file:    pass # do something　　而在Python 2.1里，你只能用xreadlines迭代器来实现：# File: readline-example-4.py file = open("sample.txt") for line in file.xreadlines():    pass # do something