如何修改python这个编码计算器里的错误

以下为错误
Test Failed: False is not true : get_expr call after step('+', 3) doesn't return a correct: should be '(0)+3'

Test Failed: False is not true : get_expr call after step('+', 3) and then repeat() doesn't return a correct: should be '((0)+3)+3'

Test Failed: False is not true : calling step() multiple times with different values and operations (like in the second writeup example) didn't produce the correct get_expr() results

Test Failed: False is not true : Second example (with both step and repeat calls) produces incorrect expressions

Test Failed: False is not true : Third example (with an initial clear, steps, and multiple repeats) produces an incorrect expression

Test Failed: False is not true : Another example not from the write-up didn't produce the correct expressions.

Test Failed: False is not true : Calling repeat immediately after calling clear(number), where number was a non-zero value, produced an incorrect output on either the value, expression, or both.

错误信息告诉你很清楚了，当调用step，你应该返回'(0)+3'这个字符串，而不是int值
回去仔细审题，再编代码，这代码写的乱糟糟的，integer都已经是全局静态变量了，你还一遍一遍return它干什么