b+=[str(a%10)] TypeError: not all arguments converted during string formatting

This error occurs when you try to convert a non-string object into a string using the string formatting method.

In this specific case, it looks like you are trying to convert an integer (a) into a string using the formatting method, but the syntax is incorrect.

To convert an integer to a string, you can simply use the str() function without any formatting. The correct syntax would be:

b = str(a)

This will convert the integer value of a into a string and store it in the variable b.