【4 points of this unit with python3】
1.TypeError: 'dict_keys' object does not support indexing

Replace this with:
    firstSide = list(myTree.keys()) 
    firstStr = firstSide[0]

As in python2,' dict. Keys ()' gets a list, while in python3, this returns the class 'dict_keys' without an order, 
so it cannot be indexed. 
To obtain a list, replace it with  'list(dict. Keys ())' to make a coercion conversion.
python2里，dict.keys()结果是一个列表，而python3中，返回的是class， 'dict_keys'没有索引顺序，不能index。
因此需要用list()强制转换成列表。

2. xoff,yoff are both lowercases
xoff,yoff 中的o都是小写

3.TypeError: write() argument must be str, not bytes。
def storeTree(inputTree, filename):
    import pickle
    fw = open(filename, 'wb')

【I/O】 'w'→'wb' √

4.UnicodeDecodeError: 'gbk' codec can't decode byte 0x80 in position 0: illegal multibyte sequence
def grabTree(filename):
    import pickle
    fr = open(filename,'rb') 

【I/O】 open(filename,'rb') √