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i want to invert the number 12345 in python like 54321 and display it

I'm new to programming.
I want to invert the number 12345 in Python like 54321 and display it.

Error message: ValueError: invalid literal for int () with base 10:''
Is displayed and it does not work
Can you tell me what was wrong with me?
Corresponding source code 
num = 12345
str_num = str (num)
x = 0
lis = []
while x<6:
    amari = int (str_num [0: 5-x])% 10
    lis.append (amari)
    x + = 1
print (lis)
result =''. join ([lis])
print (result)
What I tried

I wonder if int (str_num [0: 5-x]) is treated as a decimal number.
'{: d}'. format (int (str_num [0: 5-x]))
I converted it as, but this is also
TypeError: not all arguments converted during string formatting
I got an error

Supplementary information (FW/tool version, etc.)

It is a web learning service called PyQ

python
  • Answer # 1

    amari = int (str_num [0: 5-x])% 10
    In the above place, when x becomes 5, it becomes str_num [0: 0], which is an empty string.

    Postscript
    It seems that the character string can be inverted with str_num [:: -1].

  • Answer # 2

    It depends on what the code is for, but if you want to do what you want, it's already in the answer.str_num [:: -1]I think it's smart.

    If the purpose is to learn algorithms, etc., it can be realized by recursive call of the function.

    num = 12345
def func (n, l):
    if n<10:
        l.append (n)
        return;
    l.append (n% 10)
    n = n // 10
    func (n, l) # recursion
list1 = []
func (num, list1)
print (list1) # [5, 4, 3, 2, 1]
r =''. join ([str (item) for item in list1])
print (r) # 54321

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