I have been testing this arithmetic arranger project for the first scientific computing with python project and every time I enter one of the test inputs into the code it comes out identical to the expected output. Despite this, I keep receiving a single failure. I searched to see if anyone else had a similar problem and a solution, but I did not see one.

Here is my code:

```
def arithmetic_arranger(problems, showAns = False):
int_1_line = ""
int_2_line = ""
answer_line = ""
line_line = ""
if len(problems) > 5:
return "Error: Too many problems."
else:
for problem in problems:
int_1_end = problem.find(" ")
int_1 = (problem[0:int_1_end])
operator_end = int_1_end + 2
operator = (problem[int_1_end+1:operator_end])
int_2_end = problem[len(problem)- 1]
int_2 = (problem[operator_end+1:-1])
int_2 = int_2 + problem[-1]
if operator not in ["+", "-"]:
return "Error: Operator must be '+' or '-'."
elif isinstance(int(int_2), int) != True or isinstance(int(int_2), int) != True:
return "Error: Numbers must only contain digits."
elif len(int_1) > 4 or len(int_2) > 4:
return "Error: Numbers cannot be more than four digits."
else:
if operator in ["+"]:
answer = int(int_1) + int(int_2)
elif operator in ["-"]:
answer = int(int_1) - int(int_2)
else:
return "Error: Operator must be '+' or '-'."
big_int = max(len(str(int_1)),len(str(int_2)))
width = big_int + 2
int_1_line = int_1_line + " " + (int_1.rjust(width))
int_2_line = int_2_line + " " + (operator + (int_2.rjust(width-1)))
line = "-"*(width)
line_line += " " + line
if showAns == True:
answer = str(answer)
answer_line = answer_line + " " + (answer.rjust(width))
int_1_done = int_1_line[4:]
int_2_done = int_2_line[4:]
line_done = line_line[4:]
answer_done = answer_line[4:]
arranged_problems = int_1_done + "\n" + int_2_done + "\n" + line_done + "\n" + answer_done
return arranged_problems
```

The Repl.it link as well.