如何在Python中将字符串转换为整数

Question

""" A trimorphic number is a number whose cube ends in the number itself.

For example:

Input: 4
Output: true (4^3 is 64, which ends in 4)

Input: 24
Output: true (24^3 = 13824)

Input: 249
Output: true (249^3 = 15438249)

Write a program to check if the user input is a trimorphic number or not. """

num = int(input("Enter a number:"))
print(num)

num_cube = pow(num, 3)
str(num_cube)
print(num_cube[len(num_cube) - 1:] == num)

I tried running the code and I got a TypeError at line 22 (the last line) even though I converted the variable num_cube to a string in order to slice it. Why does it not work?

Answer 1

str(num_cube) is not assigned, so you are converting it but still using num_cube which is an int, hence the TypeError . Also, you need to compare it to another string, not to to num which is another integer:

print(str(num_cube)[-3:] == str(num))

Answer 2

You should use the endswith function to check whether the last "n" characters in the cube are equal to the string representation of the number you are passed.

You could thus do:

print(str(num_cube).endswith(num))

The way you have currently implemented it, you are "hard coding" the expected length of the number read from the stdin and are thus assuming it to always be of length 1.

To correct your code, you would do the following:

>>> num = "24"
>>> num_cube = str(pow(int(num), 3))
>>> num_cube[len(num_cube) - len(num):] == num
True
>>> num_cube[-len(num):] == num # negative indexing
True