This is unofficial parser - screen scraper - implementation for FMI website. Please check possible conditions and terms before using. This will probably break on every website update.
pip install fmiweather
from fmiweather import FmiWeather
weather = FmiWeather()
weather.download_content("http://ilmatieteenlaitos.fi/saa/helsinki/s%C3%B6rn%C3%A4inen")
print weather.parse_next_days() # Parses daily forecasts
print weather.parse_next_hours() # Parses hourly forecast
print weather.parse_observations() # Parses observations