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#!/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)
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