import os
ls = os.linesep
while True:
    fname = raw_input('Enter filename: ')
    if os.path.exists(fname):
        print "ERROR: '%s' already exists" % fname
    else:
        break
all = []
print "\nEnter lines ('.' by itself to quit).\n"
while True:
    entry = raw_input('> ')
    if entry == '.':
        break
    else:
        all.append(entry)
fobj = open(fname, 'w')
# os.linesep作为行结束符在Windows里面会产生多余的回车
# fobj.writelines(['%s%s' % (x, ls) for x in all])
# 还是用\n比较靠谱（官方帮助文档也是这样建议的）
fobj.writelines(['%s\n' % x for x in all])
# 另一个方法也行
# for x in all:
    # print >> fobj, x
fobj.close()
print 'DONE!'
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