python的文件处理，增删列的问题？
如文件原先是：
a,b,c
d,d,e
e,e,e
。。。


1，新增后变成：
a,b,k,c
d,d,k,e
e,e,k,e
。。。。

python 在第三列前增加了一列，且那一列是个常量（就是都是某个值，不变的），记录数是上千万条的，
要求速度也要快，有什么好方法？



2，
还有就是删除列
删除第2、3列后变成
a,c
d,e
e,e
。。。
记录数是上千万条的，
要求速度也要快，有什么好方法？



[解决办法]

Python code

#!/usr/bin/env pythonaText = [    ['a','b','c'],    ['d','d','e'],    ['e','e','e'],];aCol = 2for aList in aText:    print aList[0:aCol] + ['k'] + aList[aCol:]aCol = 1for aList in aText:    print aList[0:aCol] + aList[aCol + 1:]
[解决办法]
Python code
class BufferedWriter:    MAXBUFFSIZE = 16384    LINEFEED = '\n'    SPLITER = ','    def __init__(self, filename):        self.filename = filename    def __enter__(self):        self.handle = open(self.filename, 'w')        self.buffer = []        return self    def __exit__(self, *args):        if self.buffer:            self.flush()        self.handle.close()    def append(self, row):        self.buffer.append(row)        if len(self.buffer)>=self.MAXBUFFSIZE:            self.flush()    def flush(self):        self.buffer, data = [], self.buffer        self.handle.write(''.join(            map(lambda row: self.SPLITER.join(row)+self.LINEFEED, data)            ))def eachRow(filename, spliter=','):    with open(filename,'r') as handle:        for ln in handle:            yield ln.strip().split(spliter)-- add column 'k' at pos kwith BufferWriter('target.txt') as bw:    for row in eachRow('src.txt'):        bw.append(row[:k] + ['k',] + row[k:])-- del column at pos kwith BufferWriter('target.txt') as bw:    for row in eachRow('src.txt'):        bw.append(row[:k] + row[k+1:])