Python读取和写入文件

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#Read and Write from Files#
#coding=utf-8
import codecs
f = open("AccountList.txt","w")
L = u"张三\n李四\n王五\n赵六"
f.write(L)
f.close()
f = open("AccountList.txt","r")
print (f.readline())    #read lines one by one
print (f.readline())
print (f.readline())
print (f.readline())
f.seek(0)
print (f.readlines())   #Output lines as a list


import linecache
m = open("AccountList01.txt","w")
n = u"America\nChina\nJapan\nEngland\nCanda\nGermany"
m.write(n)
m.close()
#m = open("AccountList01.txt","r")
#f.seek(0)
print(linecache.getline("AccountList01.txt",1));
print(linecache.getline("AccountList01.txt",2));
print(linecache.getline("AccountList01.txt",3));
print(linecache.getline("AccountList01.txt",1));
print(linecache.getline("AccountList01.txt",4));
print(linecache.getline("AccountList01.txt",5));
print(linecache.getline("AccountList01.txt",6));

cgkmh

请问L = u"张三\n李四\n王五\n赵六"这里的u是什么参数