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 filefo = 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 lineline = fo.readline()print "Read Line: %s" % (line)line = fo.readline(5)print "Read Line: %s" % (line)# Close opend filefo.close()当我们运行上面的程序，它会产生以下结果：
Name of the file: foo.txtRead Line: This is 1st lineRead Line: This
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