编写一个接受表示多项式的列表的函数

Question

def print_poly(p):

    """
      >>> print_poly([4, 3, 2])
      4x^2 + 3x + 2
      >>> print_poly([6, 0, 5])
      6x^2 + 5
      >>> print_poly([7, 0, -3, 5])
      7x^3 - 3x + 5
      >>> print_poly([1, -1, 0, 0, -3, 2])
      x^5 - x^4 - 3x + 2
    """

    printable = ''

    for i in range(len(p) -1, -1, -1):
        poly += ('p[i]' + 'x^' + str(i))
    for item in printable:
        if 0 in item:
            item *= 0
    printable += poly[0]
    for item in poly[1:]:
        printable += item
    print(printable)

无论我尝试多少次，我就是无法让所有的测试通过。

Answer 1

我不太明白你在问什么，但我还是试着回答一下。

你想在Python中定义一个函数（你应该把这个加到你的标签里），这个函数叫做print_poly([coef0, coef1, ..., coefn])，它的输出应该是一个多项式：

coef0*x^(n) + coef1*x^(n-1) + ... + coefn

你可以试试这个：

def print_poly(list):
    polynomial = ''
    order = len(list)-1
    for coef in list:
        if coef is not 0 and order is 1:
            term = str(coef) + 'x'
            polynomial += term
        elif coef is not 0 and order is 0:
            term = str(coef)
            polynomial += term
        elif coef is not 0 and order is not 0 and order is not 1:
            term = str(coef) + 'x^' + str(order)
            polynomial += term
        elif coef is 0:
            pass

        if order is not 0 and coef is not 0:
            polynomial += ' + '
        order += -1
    print(polynomial)

这就是你的答案，但老实说，你应该自己去了解一下Python的函数定义、布尔运算符和数学运算符，因为看起来你对这些还不太熟悉。

布尔运算符 - https://docs.python.org/3.1/library/stdtypes.html

算术运算 - http://en.wikibooks.org/wiki/Python_Programming/Operators

函数 - http://en.wikibooks.org/wiki/Non-Programmer's_Tutorial_for_Python_3/Defining_Functions

如果你有决心的话，可以看看这个：
《艰难的Python学习之路》（http://learnpythonthehardway.org/）