python之featVec[:axis]｜extend｜append

features = [1,2,3,4]
retDataSet=[]
reducedFeatVec=features[:0]    
print(reducedFeatVec)
reducedFeatVec.extend(features[1:])   #从1开始往 后加进来
print(reducedFeatVec)
retDataSet.append(reducedFeatVec) #变为向量
print(retDataSet)