Please wrap code in triple backticks to preserve the formatting:
```python
if True:
print(''Hello world!')
```
input("a") == "yes" or "no" is equivalent to (input("a") == "yes") or "no", and "no" will be treated as true, so that condition will always be true no matter what you input.
What you should write instead is something like input("a") in {"yes", "no"}.
It would also be a good idea to convert what’s input to lowercase because “YES” != “yes”.