Please solve the programming task below using a self-contained code snippet in a markdown code block.

Given a string expression representing an expression of fraction addition and subtraction, return the calculation result in string format.
The final result should be an irreducible fraction. If your final result is an integer, change it to the format of a fraction that has a denominator 1. So in this case, 2 should be converted to 2/1.
 
Please complete the following python code precisely:
```python
class Solution:
    def fractionAddition(self, expression: str) -> str:
```