fileObject.readline( size );

假设 'foo.txt' 文件包含以下文本：
This is 1st line
This is 2nd line
This is 3rd line
This is 4th line
This is 5th line

#!/usr/bin/python3

# 打开一个文件
fo = open("foo.txt", "r+")
print ("文件名为：", fo.name)

line = fo.readline()
print ("读取的数据为： %s" % (line))

line = fo.readline(5)
print ("读取的数据为： %s" % (line))

# 关闭打开的文件
fo.close()

文件名为： foo.txt
读取的数据为： This is 1st line

读取的数据为： This