update python.md

则L2=[2,3,4]

## Tab对齐推荐改为4个空格

## 一个简单的程序

    while True:

        reply = input("Enter text:")

        if reply == "stop": 

            break

        elif not reply.isdigit ():

            print (reply * 3, ", you can input stop to exit!")

        else:

            num = int(reply)

            if num < 20:

                print ("low! choose another number.")

            else:

                print (num**2)

    print ("bye!")

    input ()

## 爬虫

    import urllib.request,io,os,sys

    req = urllib.request.Request("http://www.vaayne.com/2015/12/08/ciowstpdg000eyt3l737tei1z/")

    f = urllib.request.urlopen(req)

    s = f.read()

    s = s.decode('utf-8','ignore')

    mdir = sys.path[0]+'/'

    file = open(mdir+'whz.html','a',1,'utf-8')

    file.write(s)

    file.close()

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