readline()方法从文件中读取一个完整的行。结尾的换行符也保持在字符串中。如果参数 size 存在且非负，这是一个最大字节数，包括结尾的换行和不完整的行可能被返回。
当遇到EOF，一个空字符串立即被返回。
语法
下面是 readline()方法的语法-
fileObject.readline( size );
参数
-
size -- 这是从文件中读取的字节数。
返回值
此方法从文件中返回读取的行。
示例
下面的例子显示 readline() 方法的使用。
Assuming that 'foo.txt' file contains following text: This is 1st line This is 2nd line This is 3rd line This is 4th line This is 5th line
#!/usr/bin/python3
# Open a file
fo = open("foo.txt", "r+")
print ("Name of the file: ", fo.name)
line = fo.readline()
print ("Read Line: %s" % (line))
line = fo.readline(5)
print ("Read Line: %s" % (line))
# Close opened file
fo.close()
当我们运行上面的程序，会产生以下结果 -
Name of the file: foo.txt Read Line: This is 1st line Read Line: This
