#!/usr/bin/env python3 # Copyright © 2014 Mattias Andrée (maandree@member.fsf.org) # # This program is free software: you can redistribute it and/or modify # it under the terms of the GNU General Public License as published by # the Free Software Foundation, either version 3 of the License, or # (at your option) any later version. # # This program is distributed in the hope that it will be useful, # but WITHOUT ANY WARRANTY; without even the implied warranty of # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the # GNU General Public License for more details. # # You should have received a copy of the GNU General Public License # along with this program. If not, see <http://www.gnu.org/licenses/>. # The module implements support for retrieval of weather reports from subprocess import Popen, PIPE def weather(station, downloader = None): ''' Get a brief weather report Airports should publish METAR (Meteorological Aerodrome Report) reports at XX:20 and XX:50, it can presumable take some time before the collection server we use (weather.noaa.gov) have received it. Additionally some airports do not update while closed, and updates while closed are less accurate. @param station:str The station's International Civil Aviation Organization airport code @param downloader:(url:str)?→list<str> A function that, with an URL as input, returns a command to download the file at the URL to stdout @return :(sky:str, visiblity:(:int, :float)?, weather:list<str>)? The sky condition, visiblity and weather. Sky condition values include ‘clear’, ‘mostly clear’, ‘partly cloudy’, ‘mostly cloudy’, ‘overcast’ and ‘obscured’. The visibility consists of two parameters: the first on indicates the the visiblity is a upper bound if the value is -1, a lower bound if +1, and approximate if 0; the second parameter is the visibility in kilometers. If the visibility is unknown the value will be `None`. The weather is a list that can, and often is, empty. `None` is return if observation data cannot be downloaded. ''' ## URI of METAR url = 'http://weather.noaa.gov/pub/data/observations/metar/decoded/%s.TXT' url %= station.upper() ## Download METAR # Use wget if not specified if downloader is None: downloader = lambda u : ['wget', u, '-O', '-'] proc = Popen(downloader(url), stdout = PIPE, stderr = PIPE) ## Wait for download to finish and fetch output output = proc.communicate()[0] # Ignore output if it was not successful if not proc.returncode == 0: return None ## Create field table from output = output.decode('utf-8', 'replace').split('\n') output = [line.lower().split(': ') for line in output if ': ' in line] output = dict([(line[0], ': '.join(line[1:])) for line in output]) ## Get sky condition, assume clear (although often not) if omitted sky_conditions = 'clear' if 'sky conditions' not in output else output['sky conditions'] ## Get visibility range visibility = None try: if 'visibility' in output: # Remove tail digit visibility = output['visibility'].split(':')[0] # Remove unit, it is always miles the decoded part visibility = visibility.replace(' mile(s)', '') visibility = visibility.replace(' miles', '') visibility = visibility.replace(' mile', '') # Range is assumed approximate if not specified visibility_eq = 0 if visibility.startswith('greater than '): # Range is a lower bound visibility_eq = 1 visibility = visibility[len('greater than '):] if visibility.startswith('less than '): # Range is an upper bound visibility_eq = -1 visibility = visibility[len('less than '):] if len(list(filter(lambda c : not (('0' <= c <= '9') or (c in ' /.')), visibility))) == 0: # Parse mixed numeral or decimal form visibility = sum([eval(v) for v in visibility.split(' ')]) # Pack boundary information and range (converted to kilometers) visibility = (visibility_eq, visibility * 1.609) else: visibility = None except: ## `eval` failed (probably) visibility = None ## Get weather weather = '' if 'weather' not in output else output['weather'] ## Unify conjnuctions weather = weather.replace(',', ';').replace(' with ', ';') ## Remove undesired details # Not important as we are not pilots, we are probably far away weather = weather.replace(' in the vicinity', '') # Duration is not important for use either weather = weather.replace(' during the past hour', '') # Unimportant detail weather = weather.replace(' observed', '') ## Split at conjunction weather = [w.replace(';', '').strip() for w in weather.split(';') if not w == ''] return (sky_conditions, visibility, weather)