Nested list in class

I was trying to create a class BookStack() where in I wanted that the user will enter book number and name as a list and it will get appended to a already created list, thus making a nested list. My code is as follows:

class BookStack():
    def __init__(self):
        self.books=[]

    def push(self,books):
        self.books.append(books)
        print self.books

    def pop(self):
        self.books.pop()

    def __str__(self):
        for i in self.books:
            print i,'\n'

def main():
    while 1:
        print "             1. Enter Book Credentials"
        print "     2. Remove the most recent book from database"
        print "                3. Print Database"

        choice=int(raw_input("Enter Choice: "))
        if(choice==1):
            book=BookStack()
            BookNumName=input("Enter Book Name & Number as [Number,Name]: ")
            book.push(BookNumName)
        elif(choice==2):
            book.pop()
        elif(choice==3):
            book.__str__()
        proceed=raw_input("Do you want to enter more(Y/N)?: ")
        if(proceed!='y' and proceed!='Y'):
            break

if __name__=='__main__':
    main()

But If I enter a list like [1,'A'] , [2,'B'] , [3,'C'], the output is

[[3, 'C']]

The output I want:

[[1,'A'],[2,'B'],[3, 'C']]