infoex-autowx.py

   1 #!/usr/bin/env python
   2 # -*- coding: utf-8 -*-
   3
   4 """
   5 InfoEx <-> NRCS/MesoWest Auto Wx implementation
   6 Alexander Vasarab
   7 Wylark Mountaineering LLC
   8
   9 This program fetches data from either an NRCS SNOTEL site or MesoWest
  10 weather station and pushes it to InfoEx using the new automated weather
  11 system implementation.
  12
  13 It is designed to be run hourly, and it asks for the last three hours
  14 of data of each desired type, and selects the most recent one. This
  15 lends some resiliency to the process and helps ensure that we have a
  16 value to send, but it can lead to somewhat inconsistent/untruthful
  17 data if e.g. the HS is from the last hour but the tempPres is from two
  18 hours ago because the instrumentation had a hiccup. It's worth
  19 considering if this is a bug or a feature.
  20
  21 For more information, see file: README
  22 For licensing, see file: LICENSE
  23 """
  24
  25 import configparser
  26 import csv
  27 import datetime
  28 import logging
  29 import os
  30 import sys
  31 import time
  32 import urllib3
  33 import importlib.util
  34
  35 from ftplib import FTP
  36 from argparse import ArgumentParser
  37
  38 import pytz
  39
  40 import requests
  41
  42 import zeep
  43 import zeep.cache
  44 import zeep.transports
  45
  46 __version__ = '3.2.2'
  47
  48 LOG = logging.getLogger(__name__)
  49 LOG.setLevel(logging.NOTSET)
  50
  51 urllib3.disable_warnings()
  52
  53 def get_parser():
  54     """Return OptionParser for this program"""
  55     parser = ArgumentParser()
  56
  57     parser.add_argument("--version",
  58                         action="version",
  59                         version=__version__)
  60
  61     parser.add_argument("--config",
  62                         dest="config",
  63                         metavar="FILE",
  64                         help="location of config file")
  65
  66     parser.add_argument("--log-level",
  67                         dest="log_level",
  68                         default=None,
  69                         help="set the log level (debug, info, warning)")
  70
  71     parser.add_argument("--dry-run",
  72                         action="store_true",
  73                         dest="dry_run",
  74                         default=False,
  75                         help="fetch data but don't upload to InfoEx")
  76
  77     return parser
  78
  79 def setup_config(config):
  80     """Setup config variable based on values specified in the ini file"""
  81     try:
  82         infoex = {
  83             'host': config['infoex']['host'],
  84             'uuid': config['infoex']['uuid'],
  85             'api_key': config['infoex']['api_key'],
  86             'csv_filename': config['infoex']['csv_filename'],
  87             'location_uuid': config['infoex']['location_uuid'],
  88             'wx_data': {}, # placeholder key, values to come later
  89         }
  90
  91         station = dict()
  92         station['provider'] = config['station']['type']
  93
  94         if station['provider'] not in ['nrcs', 'mesowest', 'python']:
  95             print("Please specify either nrcs or mesowest as the station type.")
  96             sys.exit(1)
  97
  98         if station['provider'] == 'nrcs':
  99             station['source'] = 'https://www.wcc.nrcs.usda.gov/awdbWebService/services?WSDL'
 100             station['station_id'] = config['station']['station_id']
 101             station['desired_data'] = config['station']['desired_data'].split(',')
 102             station['units'] = config['station']['units']
 103
 104         if station['provider'] == 'mesowest':
 105             station['source'] = 'https://api.synopticdata.com/v2/stations/timeseries'
 106             station['station_id'] = config['station']['station_id']
 107             station['units'] = config['station']['units']
 108             station['desired_data'] = config['station']['desired_data']
 109
 110             # construct full API URL (sans start/end time, added later)
 111             station['source'] = station['source'] + '?token=' + \
 112                                 config['station']['token'] + \
 113                                 '&within=60&units=' + station['units'] + \
 114                                 '&stid=' + station['station_id'] + \
 115                                 '&vars=' + station['desired_data']
 116
 117         if station['provider'] == 'python':
 118             station['path'] = config['station']['path']
 119
 120         tz = 'America/Los_Angeles'
 121
 122         if 'tz' in config['station']:
 123             tz = config['station']['tz']
 124
 125         try:
 126             station['tz'] = pytz.timezone(tz)
 127         except pytz.exceptions.UnknownTimeZoneError:
 128             LOG.critical("%s is not a valid timezone", tz)
 129             sys.exit(1)
 130
 131     except KeyError as err:
 132         LOG.critical("%s not defined in configuration file", err)
 133         sys.exit(1)
 134
 135     # all sections/values present in config file, final sanity check
 136     try:
 137         for key in config.sections():
 138             for subkey in config[key]:
 139                 if not config[key][subkey]:
 140                     raise ValueError
 141     except ValueError:
 142         LOG.critical("Config value '%s.%s' is empty", key, subkey)
 143         sys.exit(1)
 144
 145     return (infoex, station)
 146
 147 def setup_logging(log_level):
 148     """Setup our logging infrastructure"""
 149     try:
 150         from systemd.journal import JournalHandler
 151         LOG.addHandler(JournalHandler())
 152     except ImportError:
 153         ## fallback to syslog
 154         #import logging.handlers
 155         #LOG.addHandler(logging.handlers.SysLogHandler())
 156         # fallback to stdout
 157         handler = logging.StreamHandler(sys.stdout)
 158         formatter = logging.Formatter('%(asctime)s.%(msecs)03d '
 159             '%(levelname)s %(module)s - %(funcName)s: %(message)s',
 160             '%Y-%m-%d %H:%M:%S')
 161         handler.setFormatter(formatter)
 162         LOG.addHandler(handler)
 163
 164     # ugly, but passable
 165     if log_level in [None, 'debug', 'info', 'warning']:
 166         if log_level == 'debug':
 167             LOG.setLevel(logging.DEBUG)
 168         elif log_level == 'info':
 169             LOG.setLevel(logging.INFO)
 170         elif log_level == 'warning':
 171             LOG.setLevel(logging.WARNING)
 172         else:
 173             LOG.setLevel(logging.NOTSET)
 174     else:
 175         return False
 176
 177     return True
 178
 179 def main():
 180     """Main routine: sort through args, decide what to do, then do it"""
 181     parser = get_parser()
 182     options = parser.parse_args()
 183
 184     config = configparser.ConfigParser(allow_no_value=False)
 185
 186     if not options.config:
 187         parser.print_help()
 188         print("\nPlease specify a configuration file via --config.")
 189         sys.exit(1)
 190
 191     config.read(options.config)
 192
 193     if not setup_logging(options.log_level):
 194         parser.print_help()
 195         print("\nPlease select an appropriate log level or remove the switch (--log-level).")
 196         sys.exit(1)
 197
 198     (infoex, station) = setup_config(config)
 199
 200     LOG.debug('Config parsed, starting up')
 201
 202     # create mappings
 203     (fmap, final_data) = setup_infoex_fields_mapping(infoex['location_uuid'])
 204     iemap = setup_infoex_counterparts_mapping(station['provider'])
 205
 206     # override units if user selected metric
 207     if station['provider'] != 'python' and station['units'] == 'metric':
 208         final_data = switch_units_to_metric(final_data, fmap)
 209
 210     (begin_date, end_date) = setup_time_values(station)
 211
 212     if station['provider'] == 'python':
 213         LOG.debug("Getting custom data from external Python program")
 214     else:
 215         LOG.debug("Getting %s data from %s to %s (%s)",
 216                   str(station['desired_data']),
 217                   str(begin_date), str(end_date), end_date.tzinfo.zone)
 218
 219     time_all_elements = time.time()
 220
 221     # get the data
 222     if station['provider'] == 'nrcs':
 223         infoex['wx_data'] = get_nrcs_data(begin_date, end_date, station)
 224     elif station['provider'] == 'mesowest':
 225         infoex['wx_data'] = get_mesowest_data(begin_date, end_date,
 226                                               station)
 227     elif station['provider'] == 'python':
 228         try:
 229             spec = importlib.util.spec_from_file_location('custom_wx',
 230                                                           station['path'])
 231             mod = importlib.util.module_from_spec(spec)
 232             spec.loader.exec_module(mod)
 233             mod.LOG = LOG
 234
 235             try:
 236                 infoex['wx_data'] = mod.get_custom_data()
 237
 238                 if infoex['wx_data'] is None:
 239                     infoex['wx_data'] = []
 240             except Exception as exc:
 241                 LOG.error("Python program for custom Wx data failed in "
 242                           "execution: %s", str(exc))
 243                 sys.exit(1)
 244
 245             LOG.info("Successfully executed external Python program")
 246         except ImportError:
 247             LOG.error("Please upgrade to Python 3.3 or later")
 248             sys.exit(1)
 249         except FileNotFoundError:
 250             LOG.error("Specified Python program for custom Wx data "
 251                       "was not found")
 252             sys.exit(1)
 253         except Exception as exc:
 254             LOG.error("A problem was encountered when attempting to "
 255                       "load your custom Wx program: %s", str(exc))
 256             sys.exit(1)
 257
 258     LOG.info("Time taken to get all data : %.3f sec", time.time() -
 259              time_all_elements)
 260
 261     LOG.debug("infoex[wx_data]: %s", str(infoex['wx_data']))
 262
 263     # timezone massaging
 264     final_end_date = end_date.astimezone(station['tz'])
 265
 266     # Now we only need to add in what we want to change thanks to that
 267     # abomination of a variable declaration earlier
 268     final_data[fmap['Location UUID']] = infoex['location_uuid']
 269     final_data[fmap['obDate']] = final_end_date.strftime('%m/%d/%Y')
 270     final_data[fmap['obTime']] = final_end_date.strftime('%H:%M')
 271     final_data[fmap['timeZone']] = station['tz'].zone
 272
 273     for element_cd in infoex['wx_data']:
 274         if element_cd not in iemap:
 275             LOG.warning("BAD KEY wx_data['%s']", element_cd)
 276             continue
 277
 278         # do the conversion before the rounding
 279         if station['provider'] == 'nrcs' and station['units'] == 'metric':
 280             infoex['wx_data'][element_cd] = convert_nrcs_units_to_metric(element_cd, infoex['wx_data'][element_cd])
 281
 282         # Massage precision of certain values to fit InfoEx's
 283         # expectations
 284         #
 285         # 0 decimal places: relative humidity, wind speed, wind
 286         #                   direction, wind gust, snow depth
 287         # 1 decimal place:  air temp, baro
 288         # Avoid transforming None values
 289         if infoex['wx_data'][element_cd] is None:
 290             continue
 291         elif element_cd in ['wind_speed', 'WSPD', 'wind_direction',
 292                             'RHUM', 'relative_humidity', 'WDIR',
 293                             'wind_gust', 'SNWD', 'snow_depth']:
 294             infoex['wx_data'][element_cd] = round(infoex['wx_data'][element_cd])
 295         elif element_cd in ['TOBS', 'air_temp', 'PRES', 'pressure']:
 296             infoex['wx_data'][element_cd] = round(infoex['wx_data'][element_cd], 1)
 297         elif element_cd in ['PREC', 'precip_accum']:
 298             infoex['wx_data'][element_cd] = round(infoex['wx_data'][element_cd], 2)
 299
 300         # CONSIDER: Casting every value to Float() -- need to investigate if
 301         #           any possible elementCds we may want are any other data
 302         #           type than float.
 303         #
 304         #           Another possibility is to query the API with
 305         #           getStationElements and temporarily store the
 306         #           storedUnitCd. But that's pretty network-intensive and
 307         #           may not even be worth it if there's only e.g. one or two
 308         #           exceptions to any otherwise uniformly Float value set.
 309         final_data[fmap[iemap[element_cd]]] = infoex['wx_data'][element_cd]
 310
 311     LOG.debug("final_data: %s", str(final_data))
 312
 313     if infoex['wx_data']:
 314         if not write_local_csv(infoex['csv_filename'], final_data):
 315             LOG.warning('Could not write local CSV file: %s',
 316                         infoex['csv_filename'])
 317             return 1
 318
 319         if not options.dry_run:
 320             upload_csv(infoex['csv_filename'], infoex)
 321
 322     LOG.debug('DONE')
 323     return 0
 324
 325 # data structure operations
 326 def setup_infoex_fields_mapping(location_uuid):
 327     """
 328     Create a mapping of InfoEx fields to the local data's indexing scheme.
 329
 330     INFOEX FIELDS
 331
 332     This won't earn style points in Python, but here we establish a couple
 333     of helpful mappings variables. The reason this is helpful is that the
 334     end result is simply an ordered set, the CSV file. But we still may
 335     want to manipulate the values arbitrarily before writing that file.
 336
 337     Also note that the current Auto Wx InfoEx documentation shows these
 338     keys in a graphical table with the "index" beginning at 1, but here we
 339     sanely index beginning at 0.
 340     """
 341     # pylint: disable=too-many-statements,multiple-statements,bad-whitespace
 342     fmap = {}                           ; final_data     = [None] * 29
 343     fmap['Location UUID'] = 0           ; final_data[0]  = location_uuid
 344     fmap['obDate'] = 1                  ; final_data[1]  = None
 345     fmap['obTime'] = 2                  ; final_data[2]  = None
 346     fmap['timeZone'] = 3                ; final_data[3]  = 'Pacific'
 347     fmap['tempMaxHour'] = 4             ; final_data[4]  = None
 348     fmap['tempMaxHourUnit'] = 5         ; final_data[5]  = 'F'
 349     fmap['tempMinHour'] = 6             ; final_data[6]  = None
 350     fmap['tempMinHourUnit'] = 7         ; final_data[7]  = 'F'
 351     fmap['tempPres'] = 8                ; final_data[8]  = None
 352     fmap['tempPresUnit'] = 9            ; final_data[9]  = 'F'
 353     fmap['precipitationGauge'] = 10     ; final_data[10] = None
 354     fmap['precipitationGaugeUnit'] = 11 ; final_data[11] = 'in'
 355     fmap['windSpeedNum'] = 12           ; final_data[12] = None
 356     fmap['windSpeedUnit'] = 13          ; final_data[13] = 'mph'
 357     fmap['windDirectionNum'] = 14       ; final_data[14] = None
 358     fmap['hS'] = 15                     ; final_data[15] = None
 359     fmap['hsUnit'] = 16                 ; final_data[16] = 'in'
 360     fmap['baro'] = 17                   ; final_data[17] = None
 361     fmap['baroUnit'] = 18               ; final_data[18] = 'inHg'
 362     fmap['rH'] = 19                     ; final_data[19] = None
 363     fmap['windGustSpeedNum'] = 20       ; final_data[20] = None
 364     fmap['windGustSpeedNumUnit'] = 21   ; final_data[21] = 'mph'
 365     fmap['windGustDirNum'] = 22         ; final_data[22] = None
 366     fmap['dewPoint'] = 23               ; final_data[23] = None
 367     fmap['dewPointUnit'] = 24           ; final_data[24] = 'F'
 368     fmap['hn24Auto'] = 25               ; final_data[25] = None
 369     fmap['hn24AutoUnit'] = 26           ; final_data[26] = 'in'
 370     fmap['hstAuto'] = 27                ; final_data[27] = None
 371     fmap['hstAutoUnit'] = 28            ; final_data[28] = 'in'
 372
 373     return (fmap, final_data)
 374
 375 def setup_infoex_counterparts_mapping(provider):
 376     """
 377     Create a mapping of the NRCS/MesoWest fields that this program supports to
 378     their InfoEx counterparts
 379     """
 380     iemap = {}
 381
 382     if provider == 'nrcs':
 383         iemap['PREC'] = 'precipitationGauge'
 384         iemap['TOBS'] = 'tempPres'
 385         iemap['TMAX'] = 'tempMaxHour'
 386         iemap['TMIN'] = 'tempMinHour'
 387         iemap['SNWD'] = 'hS'
 388         iemap['PRES'] = 'baro'
 389         iemap['RHUM'] = 'rH'
 390         iemap['WSPD'] = 'windSpeedNum'
 391         iemap['WDIR'] = 'windDirectionNum'
 392         # unsupported by NRCS:
 393         # windGustSpeedNum
 394     elif provider == 'mesowest':
 395         iemap['precip_accum'] = 'precipitationGauge'
 396         iemap['air_temp'] = 'tempPres'
 397         iemap['air_temp_high_24_hour'] = 'tempMaxHour'
 398         iemap['air_temp_low_24_hour'] = 'tempMinHour'
 399         iemap['snow_depth'] = 'hS'
 400         iemap['pressure'] = 'baro'
 401         iemap['relative_humidity'] = 'rH'
 402         iemap['wind_speed'] = 'windSpeedNum'
 403         iemap['wind_direction'] = 'windDirectionNum'
 404         iemap['wind_gust'] = 'windGustSpeedNum'
 405     elif provider == 'python':
 406         # we expect Python programs to use the InfoEx data type names
 407         iemap['precipitationGauge'] = 'precipitationGauge'
 408         iemap['tempPres'] = 'tempPres'
 409         iemap['tempMaxHour'] = 'tempMaxHour'
 410         iemap['tempMinHour'] = 'tempMinHour'
 411         iemap['hS'] = 'hS'
 412         iemap['baro'] = 'baro'
 413         iemap['rH'] = 'rH'
 414         iemap['windSpeedNum'] = 'windSpeedNum'
 415         iemap['windDirectionNum'] = 'windDirectionNum'
 416         iemap['windGustSpeedNum'] = 'windGustSpeedNum'
 417
 418     return iemap
 419
 420 # provider-specific operations
 421 def get_nrcs_data(begin, end, station):
 422     """get the data we're after from the NRCS WSDL"""
 423     transport = zeep.transports.Transport(cache=zeep.cache.SqliteCache())
 424     transport.session.verify = False
 425     client = zeep.Client(wsdl=station['source'], transport=transport)
 426     remote_data = {}
 427
 428     # massage begin/end date format
 429     begin_date_str = begin.strftime('%Y-%m-%d %H:%M:00')
 430     end_date_str = end.strftime('%Y-%m-%d %H:%M:00')
 431
 432     for element_cd in station['desired_data']:
 433         time_element = time.time()
 434
 435         # get the last three hours of data for this elementCd/element_cd
 436         tmp = client.service.getHourlyData(
 437             stationTriplets=[station['station_id']],
 438             elementCd=element_cd,
 439             ordinal=1,
 440             beginDate=begin_date_str,
 441             endDate=end_date_str)
 442
 443         LOG.info("Time to get NRCS elementCd '%s': %.3f sec", element_cd,
 444                  time.time() - time_element)
 445
 446         values = tmp[0]['values']
 447
 448         # sort and isolate the most recent
 449         #
 450         # NOTE: we do this because sometimes there are gaps in hourly data
 451         #       in NRCS; yes, we may end up with slightly inaccurate data,
 452         #       so perhaps this decision will be re-evaluated in the future
 453         if values:
 454             ordered = sorted(values, key=lambda t: t['dateTime'], reverse=True)
 455             remote_data[element_cd] = ordered[0]['value']
 456         else:
 457             remote_data[element_cd] = None
 458
 459     return remote_data
 460
 461 def get_mesowest_data(begin, end, station):
 462     """get the data we're after from the MesoWest/Synoptic API"""
 463     remote_data = {}
 464
 465     # massage begin/end date format
 466     begin_date_str = begin.strftime('%Y%m%d%H%M')
 467     end_date_str = end.strftime('%Y%m%d%H%M')
 468
 469     # construct final, completed API URL
 470     api_req_url = station['source'] + '&start=' + begin_date_str + '&end=' + end_date_str
 471
 472     try:
 473         req = requests.get(api_req_url)
 474     except requests.exceptions.ConnectionError:
 475         LOG.error("Could not connect to '%s'", api_req_url)
 476         sys.exit(1)
 477
 478     try:
 479         json = req.json()
 480     except ValueError:
 481         LOG.error("Bad JSON in MesoWest response")
 482         sys.exit(1)
 483
 484     try:
 485         observations = json['STATION'][0]['OBSERVATIONS']
 486     except KeyError as exc:
 487         LOG.error("Unexpected JSON in MesoWest response: '%s'", exc)
 488         sys.exit(1)
 489     except IndexError as exc:
 490         LOG.error("Unexpected JSON in MesoWest response: '%s'", exc)
 491         try:
 492             LOG.error("Detailed MesoWest response: '%s'",
 493                       json['SUMMARY']['RESPONSE_MESSAGE'])
 494         except KeyError:
 495             pass
 496         sys.exit(1)
 497     except ValueError as exc:
 498         LOG.error("Bad JSON in MesoWest response: '%s'", exc)
 499         sys.exit(1)
 500
 501     pos = len(observations['date_time']) - 1
 502
 503     for element_cd in station['desired_data'].split(','):
 504         # sort and isolate the most recent, see note above in NRCS for how and
 505         # why this is done
 506         #
 507         # NOTE: Unlike in the NRCS case, the MesoWest API response contains all
 508         #       data (whereas with NRCS, we have to make a separate request for
 509         #       each element we want). This is nice for network efficiency but
 510         #       it means we have to handle this part differently for each.
 511         #
 512         # NOTE: Also unlike NRCS, MesoWest provides more granular data; NRCS
 513         #       provides hourly data, but MesoWest can often provide data every
 514         #       10 minutes -- though this provides more opportunity for
 515         #       irregularities
 516
 517         # we may not have the data at all
 518         key_name = element_cd + '_set_1'
 519
 520         if key_name in observations:
 521             if observations[key_name][pos]:
 522                 remote_data[element_cd] = observations[key_name][pos]
 523
 524                 # mesowest by default provides wind_speed in m/s, but
 525                 # we specify 'english' units in the request; either way,
 526                 # we want mph
 527                 if element_cd in ('wind_speed', 'wind_gust'):
 528                     remote_data[element_cd] = kn_to_mph(remote_data[element_cd])
 529             else:
 530                 remote_data[element_cd] = None
 531         else:
 532             remote_data[element_cd] = None
 533
 534     return remote_data
 535
 536 def switch_units_to_metric(data_map, mapping):
 537     """replace units with metric counterparts"""
 538
 539     # NOTE: to update this, use the fmap<->final_data mapping laid out
 540     #       in setup_infoex_fields_mapping ()
 541     data_map[mapping['tempMaxHourUnit']] = 'C'
 542     data_map[mapping['tempMinHourUnit']] = 'C'
 543     data_map[mapping['tempPresUnit']] = 'C'
 544     data_map[mapping['precipitationGaugeUnit']] = 'mm'
 545     data_map[mapping['hsUnit']] = 'cm'
 546     data_map[mapping['windSpeedUnit']] = 'm/s'
 547     data_map[mapping['windGustSpeedNumUnit']] = 'm/s'
 548     data_map[mapping['dewPointUnit']] = 'C'
 549     data_map[mapping['hn24AutoUnit']] = 'cm'
 550     data_map[mapping['hstAutoUnit']] = 'cm'
 551
 552     return data_map
 553
 554 def convert_nrcs_units_to_metric(element_cd, value):
 555     """convert NRCS values from English to metric"""
 556     if element_cd == 'TOBS':
 557         value = f_to_c(value)
 558     elif element_cd == 'SNWD':
 559         value = in_to_cm(value)
 560     elif element_cd == 'PREC':
 561         value = in_to_mm(value)
 562     return value
 563
 564 # CSV operations
 565 def write_local_csv(path_to_file, data):
 566     """Write the specified CSV file to disk"""
 567     with open(path_to_file, 'w') as file_object:
 568         # The requirement is that empty values are represented in the CSV
 569         # file as "", csv.QUOTE_NONNUMERIC achieves that
 570         LOG.debug("writing CSV file '%s'", path_to_file)
 571         writer = csv.writer(file_object, quoting=csv.QUOTE_NONNUMERIC)
 572         writer.writerow(data)
 573         file_object.close()
 574     return True
 575
 576 def upload_csv(path_to_file, infoex_data):
 577     """Upload the specified CSV file to InfoEx FTP and remove the file"""
 578     with open(path_to_file, 'rb') as file_object:
 579         LOG.debug("uploading FTP file '%s'", infoex_data['host'])
 580         ftp = FTP(infoex_data['host'], infoex_data['uuid'],
 581                   infoex_data['api_key'])
 582         ftp.storlines('STOR ' + path_to_file, file_object)
 583         ftp.close()
 584         file_object.close()
 585     os.remove(path_to_file)
 586
 587 # other miscellaneous routines
 588 def setup_time_values(station):
 589     """establish time bounds of data request(s)"""
 590
 591     # default timezone to UTC (for MesoWest)
 592     tz = pytz.utc
 593
 594     # but for NRCS, use the config-specified timezone
 595     if station['provider'] == 'nrcs':
 596         tz = station['tz']
 597
 598     # floor time to nearest hour
 599     date_time = datetime.datetime.now(tz=tz)
 600     end_date = date_time - datetime.timedelta(minutes=date_time.minute % 60,
 601                                               seconds=date_time.second,
 602                                               microseconds=date_time.microsecond)
 603     begin_date = end_date - datetime.timedelta(hours=3)
 604     return (begin_date, end_date)
 605
 606 def f_to_c(f):
 607     """convert Fahrenheit to Celsius"""
 608     return (float(f) - 32) * 5.0/9.0
 609
 610 def in_to_cm(inches):
 611     """convert inches to centimetrs"""
 612     return float(inches) * 2.54
 613
 614 def in_to_mm(inches):
 615     """convert inches to millimeters"""
 616     return (float(inches) * 2.54) * 10.0
 617
 618 def ms_to_mph(ms):
 619     """convert meters per second to miles per hour"""
 620     return ms * 2.236936
 621
 622 def kn_to_mph(kn):
 623     """convert knots to miles per hour"""
 624     return kn * 1.150779
 625
 626 if __name__ == "__main__":
 627     sys.exit(main())