Could this final_url created as:
```python
wavelength_prefix = 'tcz' if kwargs['wavelength'] == '34' else 'tca'
final_url = date.strftime(baseurl + '%Y/%m/'+wavelength_prefix+'%y%m%d')
```
I don't think there's really need to use os in here... I even think this could have an undesired effect in Windows...