readline()方法从文件中读取一整行。尾部的换行符保持在字符串中。如果大小参数且非负，那么一个最大字节数，包括结尾的换行和不完整的行可能会返回。
遇到EOF时立即返回一个空字符串。
语法
以下是readline()方法的语法：
fileObject.readline( size );
参数
返回值
此方法返回从文件中读取的行。
例子
下面的例子显示了readline()方法的使用。
#!/usr/bin/python
# Open a file
fo = open("foo.txt", "rw+")
print "Name of the file: ", fo.name
# Assuming file has following 5 lines
# This is 1st line
# This is 2nd line
# This is 3rd line
# This is 4th line
# This is 5th line
line = fo.readline()
print "Read Line: %s" % (line)
line = fo.readline(5)
print "Read Line: %s" % (line)
# Close opend file
fo.close()
当我们运行上面的程序，它会产生以下结果：
Name of the file: foo.txt Read Line: This is 1st line Read Line: This
