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# Source code for pywws.DataStore

    # pywws - Python software for USB Wireless Weather Stations
    # http://github.com/jim-easterbrook/pywws
    # Copyright (C) 2008-13  Jim Easterbrook  jim@jim-easterbrook.me.uk

    # 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 2
    # 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, write to the Free Software
    # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.

    """
    DataStore.py - stores readings in easy to access files

    Introduction
    ------------

    This module is at the core of pywws. It stores data on disc, but
    without the overhead of a full scale database system. I have designed
    it to run on a small memory machine such as my Asus router. To
    minimise memory usage it only loads one day's worth of raw data at a
    time into memory.

    From a "user" point of view, the data is accessed as a cross between a
    list and a dictionary. Each data record is indexed by a
    :py:class:`datetime.datetime` object (dictionary behaviour), but
    records are stored in order and can be accessed as slices (list
    behaviour).

    For example, to access the hourly data for Christmas day 2009, one
    might do the following::

      from datetime import datetime
      from pywws import DataStore
      hourly = DataStore.hourly_store('weather_data')
      for data in hourly[datetime(2009, 12, 25):datetime(2009, 12, 26)]:
          print data['idx'], data['temp_out']

    Some more examples of data access::

      # get value nearest 9:30 on Christmas day 2008
      data[data.nearest(datetime(2008, 12, 25, 9, 30))]
      # get entire array, equivalent to data[:]
      data[datetime.min:datetime.max]
      # get last 12 hours worth of data
      data[datetime.utcnow() - timedelta(hours=12):]

    Note that the :py:class:`datetime.datetime` index is in UTC. You may
    need to apply an offset to convert to local time.

    The module provides five classes to store different data.
    :py:class:`data_store` takes "raw" data from the weather station;
    :py:class:`calib_store`, :py:class:`hourly_store`,
    :py:class:`daily_store` and :py:class:`monthly_store` store processed
    data (see :py:mod:`pywws.Process`). All three are derived from the
    same ``core_store`` class, they only differ in the keys and types of
    data stored in each record.

    Detailed API
    ------------

    """

    from ConfigParser import RawConfigParser
    import csv
    from datetime import date, datetime, timedelta, MAXYEAR
    import os
    import sys
    import time

    DAY = timedelta(days=1)

    def safestrptime(date_string, format=None):
        # time.strptime is time consuming (because it's so flexible?) so don't use
        # it for the fixed format datetime strings in our csv files
        if format:
            return datetime(*(time.strptime(date_string, format)[0:6]))
        return datetime(*map(int, (date_string[0:4],
                                   date_string[5:7],
                                   date_string[8:10],
                                   date_string[11:13],
                                   date_string[14:16],
                                   date_string[17:19])))

    class ParamStore(object):
        def __init__(self, root_dir, file_name):
            if not os.path.isdir(root_dir):
                os.makedirs(root_dir)
            self._path = os.path.join(root_dir, file_name)
            self._dirty = False
            # open config file
            self._config = RawConfigParser()
            self._config.read(self._path)

        def __del__(self):
            self.flush()

        def flush(self):
            if not self._dirty:
                return
            self._dirty = False
            of = open(self._path, 'w')
            self._config.write(of)
            of.close()

        def get(self, section, option, default=None):
            """Get a parameter value and return a string.

            If default is specified and section or option are not defined
            in the file, they are created and set to default, which is
            then the return value.

            """
            if not self._config.has_option(section, option):
                if default is not None:
                    self.set(section, option, default)
                return default
            return self._config.get(section, option)

        def get_datetime(self, section, option, default=None):
            result = self.get(section, option, default)
            if result:
                return safestrptime(result)
            return result

        def set(self, section, option, value):
            """Set option in section to string value."""
            if not self._config.has_section(section):
                self._config.add_section(section)
            elif (self._config.has_option(section, option) and
                  self._config.get(section, option) == value):
                return
            self._config.set(section, option, value)
            self._dirty = True

        def unset(self, section, option):
            """Remove option from section."""
            if not self._config.has_section(section):
                return
            if self._config.has_option(section, option):
                self._config.remove_option(section, option)
                self._dirty = True
            if not self._config.options(section):
                self._config.remove_section(section)
                self._dirty = True

    class params(ParamStore):
        def __init__(self, root_dir):
            """Parameters are stored in a file "weather.ini" in root_dir."""
            ParamStore.__init__(self, root_dir, 'weather.ini')

    class status(ParamStore):
        def __init__(self, root_dir):
            """Status is stored in a file "status.ini" in root_dir."""
            ParamStore.__init__(self, root_dir, 'status.ini')

    class _Cache(object):
        def __init__(self):
            self.data = []
            self.ptr = 0
            self.path = ''
            self.lo = date.max
            self.hi = date.min
            self.dirty = False

        def copy(self, other):
            self.data = other.data
            self.ptr = other.ptr
            self.path = other.path
            self.lo = other.lo
            self.hi = other.hi
            self.dirty = False

        def set_ptr(self, idx):
            hi = len(self.data) - 1
            if hi < 0 or self.data[0]['idx'] >= idx:
                self.ptr = 0
                return
            if self.data[hi]['idx'] < idx:
                self.ptr = hi + 1
                return
            lo = 0
            start = min(self.ptr, hi)
            if self.data[start]['idx'] < idx:
                lo = start
            else:
                hi = start
            while hi > lo + 1:
                mid = (lo + hi) // 2
                if self.data[mid]['idx'] < idx:
                    lo = mid
                else:
                    hi = mid
            self.ptr = hi

    class core_store(object):
        def __init__(self, root_dir):
            self._root_dir = root_dir
            # initialise caches
            self._wr_cache = _Cache()
            self._rd_cache = _Cache()
            # get conservative first and last days for which data (might) exist
            self._lo_limit = date.max - timedelta(days=500)
            self._hi_limit = date.min + timedelta(days=500)
            for root, dirs, files in os.walk(self._root_dir):
                files.sort()
                for file in files:
                    if file[0] == '.':
                        continue
                    path, self._lo_limit, hi = self._get_cache_path(
                        safestrptime(file, "%Y-%m-%d.txt").date())
                    break
                else:
                    dirs.sort()
                    continue
                break
            for root, dirs, files in os.walk(self._root_dir):
                files.sort()
                files.reverse()
                for file in files:
                    if file[0] == '.':
                        continue
                    path, lo, self._hi_limit = self._get_cache_path(
                        safestrptime(file, "%Y-%m-%d.txt").date())
                    break
                else:
                    dirs.sort()
                    dirs.reverse()
                    continue
                break
            self._lo_limit_dt = datetime(
                self._lo_limit.year, self._lo_limit.month, self._lo_limit.day)
            self._hi_limit_dt = datetime(
                self._hi_limit.year, self._hi_limit.month, self._hi_limit.day)

        def __del__(self):
            self.flush()

        def _slice(self, i):
            if i.step is not None:
                raise TypeError("slice step not permitted")
            a = i.start
            if a is None:
                a = self._lo_limit_dt
            elif not isinstance(a, datetime):
                raise TypeError("slice indices must be %s or None" % (datetime))
            elif a < self._lo_limit_dt:
                a = self._lo_limit_dt
            b = i.stop
            if b is None:
                b = self._hi_limit_dt
            elif not isinstance(b, datetime):
                raise TypeError("slice indices must be %s or None" % (datetime))
            elif b > self._hi_limit_dt:
                b = self._hi_limit_dt
            return a, b

        def _get_slice(self, i):
            a, b = self._slice(i)
            if a > b:
                return
            # go to start of slice
            self._set_cache_ptr(self._rd_cache, a)
            cache = self._rd_cache.data
            cache_hi = self._rd_cache.hi
            cache_ptr = self._rd_cache.ptr
            # iterate over complete caches
            while cache_hi <= b.date():
                for data in cache[cache_ptr:]:
                    yield data
                if cache_hi >= self._hi_limit:
                    return
                self._load(self._rd_cache, cache_hi)
                cache = self._rd_cache.data
                cache_hi = self._rd_cache.hi
                cache_ptr = 0
            # iterate over part of cache
            for data in cache[cache_ptr:]:
                if data['idx'] >= b:
                    return
                yield data

        def __getitem__(self, i):
            """Return the data item or items with index i.

            i must be a datetime object or a slice.
            If i is a single datetime then a value with that index must exist."""
            if isinstance(i, slice):
                return self._get_slice(i)
            if not isinstance(i, datetime):
                raise TypeError("list indices must be %s" % (datetime))
            self._set_cache_ptr(self._rd_cache, i)
            if (self._rd_cache.ptr >= len(self._rd_cache.data) or
                self._rd_cache.data[self._rd_cache.ptr]['idx'] != i):
                raise KeyError(i)
            return self._rd_cache.data[self._rd_cache.ptr]

        def __setitem__(self, i, x):
            """Store a value x with index i.

            i must be a datetime object.
            If there is already a value with index i, it is overwritten.
            """
            if not isinstance(i, datetime):
                raise TypeError("index '%s' is not %s" % (i, datetime))
            x['idx'] = i
            self._set_cache_ptr(self._wr_cache, i)
            if len(self._wr_cache.data) == 0:
                self._lo_limit = min(self._lo_limit, self._wr_cache.lo)
                self._hi_limit = max(self._hi_limit, self._wr_cache.hi)
                self._lo_limit_dt = datetime(
                    self._lo_limit.year, self._lo_limit.month, self._lo_limit.day)
                self._hi_limit_dt = datetime(
                    self._hi_limit.year, self._hi_limit.month, self._hi_limit.day)
            if (self._wr_cache.ptr < len(self._wr_cache.data) and
                self._wr_cache.data[self._wr_cache.ptr]['idx'] == i):
                self._wr_cache.data[self._wr_cache.ptr] = x
            else:
                self._wr_cache.data.insert(self._wr_cache.ptr, x)
            self._wr_cache.dirty = True

        def _del_slice(self, i):
            a, b = self._slice(i)
            if a > b:
                return
            # go to start of slice
            self._set_cache_ptr(self._wr_cache, a)
            # delete to end of cache
            while self._wr_cache.hi <= b.date():
                del self._wr_cache.data[self._wr_cache.ptr:]
                self._wr_cache.dirty = True
                if self._wr_cache.hi >= self._hi_limit:
                    return
                self._load(self._wr_cache, self._wr_cache.hi)
                self._wr_cache.ptr = 0
            # delete part of cache
            ptr = self._wr_cache.ptr
            self._wr_cache.set_ptr(b)
            del self._wr_cache.data[ptr:self._wr_cache.ptr]
            self._wr_cache.dirty = True

        def __delitem__(self, i):
            """Delete the data item or items with index i.

            i must be a datetime object or a slice.
            If i is a single datetime then a value with that index must exist."""
            if isinstance(i, slice):
                return self._del_slice(i)
            if not isinstance(i, datetime):
                raise TypeError("list indices must be %s" % (datetime))
            self._set_cache_ptr(self._wr_cache, i)
            if (self._wr_cache.ptr >= len(self._wr_cache.data) or
                self._wr_cache.data[self._wr_cache.ptr]['idx'] != i):
                raise KeyError(i)
            del self._wr_cache.data[self._wr_cache.ptr]
            self._wr_cache.dirty = True

        def before(self, idx):
            """Return datetime of newest existing data record whose
            datetime is < idx.

            Might not even be in the same year! If no such record exists,
            return None."""
            if not isinstance(idx, datetime):
                raise TypeError("'%s' is not %s" % (idx, datetime))
            day = min(idx.date(), self._hi_limit - DAY)
            while day >= self._lo_limit:
                if day < self._rd_cache.lo or day >= self._rd_cache.hi:
                    self._load(self._rd_cache, day)
                self._rd_cache.set_ptr(idx)
                if self._rd_cache.ptr > 0:
                    return self._rd_cache.data[self._rd_cache.ptr - 1]['idx']
                day = self._rd_cache.lo - DAY
            return None

        def after(self, idx):
            """Return datetime of oldest existing data record whose
            datetime is >= idx.

            Might not even be in the same year! If no such record exists,
            return None."""
            if not isinstance(idx, datetime):
                raise TypeError("'%s' is not %s" % (idx, datetime))
            day = max(idx.date(), self._lo_limit)
            while day < self._hi_limit:
                if day < self._rd_cache.lo or day >= self._rd_cache.hi:
                    self._load(self._rd_cache, day)
                self._rd_cache.set_ptr(idx)
                if self._rd_cache.ptr < len(self._rd_cache.data):
                    return self._rd_cache.data[self._rd_cache.ptr]['idx']
                day = self._rd_cache.hi
            return None

        def nearest(self, idx):
            """Return datetime of record whose datetime is nearest idx."""
            hi = self.after(idx)
            lo = self.before(idx)
            if hi is None:
                return lo
            if lo is None:
                return hi
            if abs(hi - idx) < abs(lo - idx):
                return hi
            return lo

        def _set_cache_ptr(self, cache, i):
            day = i.date()
            if day < cache.lo or day >= cache.hi:
                self._load(cache, day)
            cache.set_ptr(i)

        def _load(self, cache, target_date):
            self._flush(cache)
            new_path, new_lo, new_hi = self._get_cache_path(target_date)
            if new_path == self._wr_cache.path:
                cache.copy(self._wr_cache)
                return
            if new_path == self._rd_cache.path:
                cache.copy(self._rd_cache)
                return
            cache.data = []
            cache.ptr = 0
            cache.path, cache.lo, cache.hi = new_path, new_lo, new_hi
            if not os.path.exists(cache.path):
                return
            if sys.version_info[0] >= 3:
                csvfile = open(cache.path, 'r', newline='')
            else:
                csvfile = open(cache.path, 'rb')
            reader = csv.reader(csvfile, quoting=csv.QUOTE_NONE)
            for row in reader:
                result = {}
                for key, value in zip(self.key_list, row):
                    if value == '':
                        result[key] = None
                    else:
                        result[key] = self.conv[key](value)
                cache.data.append(result)
            csvfile.close()

        def flush(self):
            self._flush(self._wr_cache)
            self._flush(self._rd_cache)

        def _flush(self, cache):
            if not cache.dirty:
                return
            cache.dirty = False
            if len(cache.data) == 0:
                if os.path.exists(cache.path):
                    # existing data has been wiped, so delete file
                    os.unlink(cache.path)
                return
            dir = os.path.dirname(cache.path)
            if not os.path.isdir(dir):
                os.makedirs(dir)
            if sys.version_info[0] >= 3:
                csvfile = open(cache.path, 'w', newline='')
            else:
                csvfile = open(cache.path, 'wb')
            writer = csv.writer(csvfile, quoting=csv.QUOTE_NONE)
            for data in cache.data:
                row = []
                for key in self.key_list[0:len(data)]:
                    if isinstance(data[key], float):
                        row.append(str(data[key]))
                    else:
                        row.append(data[key])
                writer.writerow(row)
            csvfile.close()

        def _get_cache_path(self, target_date):
            # default implementation - one file per day
            path = os.path.join(self._root_dir,
                                target_date.strftime("%Y"),
                                target_date.strftime("%Y-%m"),
                                target_date.strftime("%Y-%m-%d.txt"))
            lo = min(target_date, date.max - DAY)
            hi = lo + DAY
            return path, lo, hi

    class data_store(core_store):
        """Stores raw weather station data."""
        def __init__(self, root_dir):
            core_store.__init__(self, os.path.join(root_dir, 'raw'))

        key_list = [
            'idx', 'delay', 'hum_in', 'temp_in', 'hum_out', 'temp_out',
            'abs_pressure', 'wind_ave', 'wind_gust', 'wind_dir', 'rain',
            'status', 'illuminance', 'uv',
            ]
        conv = {
            'idx'          : safestrptime,
            'delay'        : int,
            'hum_in'       : int,
            'temp_in'      : float,
            'hum_out'      : int,
            'temp_out'     : float,
            'abs_pressure' : float,
            'wind_ave'     : float,
            'wind_gust'    : float,
            'wind_dir'     : int,
            'rain'         : float,
            'status'       : int,
            'illuminance'  : float,
            'uv'           : int,
            }

    class calib_store(core_store):
        """Stores 'calibrated' weather station data."""
        def __init__(self, root_dir):
            core_store.__init__(self, os.path.join(root_dir, 'calib'))

        key_list = [
            'idx', 'delay', 'hum_in', 'temp_in', 'hum_out', 'temp_out',
            'abs_pressure', 'rel_pressure', 'wind_ave', 'wind_gust', 'wind_dir',
            'rain', 'status', 'illuminance', 'uv',
            ]
        conv = {
            'idx'          : safestrptime,
            'delay'        : int,
            'hum_in'       : int,
            'temp_in'      : float,
            'hum_out'      : int,
            'temp_out'     : float,
            'abs_pressure' : float,
            'rel_pressure' : float,
            'wind_ave'     : float,
            'wind_gust'    : float,
            'wind_dir'     : int,
            'rain'         : float,
            'status'       : int,
            'illuminance'  : float,
            'uv'           : int,
            }

    class hourly_store(core_store):
        """Stores hourly summary weather station data."""
        def __init__(self, root_dir):
            core_store.__init__(self, os.path.join(root_dir, 'hourly'))

        key_list = [
            'idx', 'hum_in', 'temp_in', 'hum_out', 'temp_out',
            'abs_pressure', 'rel_pressure', 'pressure_trend',
            'wind_ave', 'wind_gust', 'wind_dir', 'rain', 'illuminance', 'uv',
            ]
        conv = {
            'idx'               : safestrptime,
            'hum_in'            : int,
            'temp_in'           : float,
            'hum_out'           : int,
            'temp_out'          : float,
            'abs_pressure'      : float,
            'rel_pressure'      : float,
            'pressure_trend'    : float,
            'wind_ave'          : float,
            'wind_gust'         : float,
            'wind_dir'          : int,
            'rain'              : float,
            'illuminance'       : float,
            'uv'                : int,
            }

    class daily_store(core_store):
        """Stores daily summary weather station data."""
        def __init__(self, root_dir):
            core_store.__init__(self, os.path.join(root_dir, 'daily'))

        key_list = [
            'idx', 'start',
            'hum_out_ave',
            'hum_out_min', 'hum_out_min_t', 'hum_out_max', 'hum_out_max_t',
            'temp_out_ave',
            'temp_out_min', 'temp_out_min_t', 'temp_out_max', 'temp_out_max_t',
            'hum_in_ave',
            'hum_in_min', 'hum_in_min_t', 'hum_in_max', 'hum_in_max_t',
            'temp_in_ave',
            'temp_in_min', 'temp_in_min_t', 'temp_in_max', 'temp_in_max_t',
            'abs_pressure_ave',
            'abs_pressure_min', 'abs_pressure_min_t',
            'abs_pressure_max', 'abs_pressure_max_t',
            'rel_pressure_ave',
            'rel_pressure_min', 'rel_pressure_min_t',
            'rel_pressure_max', 'rel_pressure_max_t',
            'wind_ave', 'wind_gust', 'wind_gust_t', 'wind_dir',
            'rain',
            'illuminance_ave', 'illuminance_max', 'illuminance_max_t',
            'uv_ave', 'uv_max', 'uv_max_t',
            ]
        conv = {
            'idx'                : safestrptime,
            'start'              : safestrptime,
            'hum_out_ave'        : float,
            'hum_out_min'        : int,
            'hum_out_min_t'      : safestrptime,
            'hum_out_max'        : int,
            'hum_out_max_t'      : safestrptime,
            'temp_out_ave'       : float,
            'temp_out_min'       : float,
            'temp_out_min_t'     : safestrptime,
            'temp_out_max'       : float,
            'temp_out_max_t'     : safestrptime,
            'hum_in_ave'         : float,
            'hum_in_min'         : int,
            'hum_in_min_t'       : safestrptime,
            'hum_in_max'         : int,
            'hum_in_max_t'       : safestrptime,
            'temp_in_ave'        : float,
            'temp_in_min'        : float,
            'temp_in_min_t'      : safestrptime,
            'temp_in_max'        : float,
            'temp_in_max_t'      : safestrptime,
            'abs_pressure_ave'   : float,
            'abs_pressure_min'   : float,
            'abs_pressure_min_t' : safestrptime,
            'abs_pressure_max'   : float,
            'abs_pressure_max_t' : safestrptime,
            'rel_pressure_ave'   : float,
            'rel_pressure_min'   : float,
            'rel_pressure_min_t' : safestrptime,
            'rel_pressure_max'   : float,
            'rel_pressure_max_t' : safestrptime,
            'wind_ave'           : float,
            'wind_gust'          : float,
            'wind_gust_t'        : safestrptime,
            'wind_dir'           : int,
            'rain'               : float,
            'illuminance_ave'    : float,
            'illuminance_max'    : float,
            'illuminance_max_t'  : safestrptime,
            'uv_ave'             : float,
            'uv_max'             : int,
            'uv_max_t'           : safestrptime,
            }

        def _get_cache_path(self, target_date):
            # one file per month
            path = os.path.join(self._root_dir,
                                target_date.strftime("%Y"),
                                target_date.strftime("%Y-%m-01.txt"))
            lo = target_date.replace(day=1)
            if lo.month < 12:
                hi = lo.replace(month=lo.month+1)
            elif lo.year < MAXYEAR:
                hi = lo.replace(year=lo.year+1, month=1)
            else:
                hi = lo
                lo = hi.replace(month=hi.month-1)
            return path, lo, hi

    class monthly_store(core_store):
        """Stores monthly summary weather station data."""
        def __init__(self, root_dir):
            core_store.__init__(self, os.path.join(root_dir, 'monthly'))

        key_list = [
            'idx', 'start',
            'hum_out_ave',
            'hum_out_min', 'hum_out_min_t', 'hum_out_max', 'hum_out_max_t',
            'temp_out_ave',
            'temp_out_min_lo', 'temp_out_min_lo_t',
            'temp_out_min_hi', 'temp_out_min_hi_t', 'temp_out_min_ave',
            'temp_out_max_lo', 'temp_out_max_lo_t',
            'temp_out_max_hi', 'temp_out_max_hi_t', 'temp_out_max_ave',
            'hum_in_ave',
            'hum_in_min', 'hum_in_min_t', 'hum_in_max', 'hum_in_max_t',
            'temp_in_ave',
            'temp_in_min_lo', 'temp_in_min_lo_t',
            'temp_in_min_hi', 'temp_in_min_hi_t', 'temp_in_min_ave',
            'temp_in_max_lo', 'temp_in_max_lo_t',
            'temp_in_max_hi', 'temp_in_max_hi_t', 'temp_in_max_ave',
            'abs_pressure_ave',
            'abs_pressure_min', 'abs_pressure_min_t',
            'abs_pressure_max', 'abs_pressure_max_t',
            'rel_pressure_ave',
            'rel_pressure_min', 'rel_pressure_min_t',
            'rel_pressure_max', 'rel_pressure_max_t',
            'wind_ave', 'wind_gust', 'wind_gust_t', 'wind_dir',
            'rain', 'rain_days',
            'illuminance_ave',
            'illuminance_max_lo', 'illuminance_max_lo_t',
            'illuminance_max_hi', 'illuminance_max_hi_t', 'illuminance_max_ave',
            'uv_ave',
            'uv_max_lo', 'uv_max_lo_t', 'uv_max_hi', 'uv_max_hi_t', 'uv_max_ave',
            ]
        conv = {
            'idx'                  : safestrptime,
            'start'                : safestrptime,
            'hum_out_ave'          : float,
            'hum_out_min'          : int,
            'hum_out_min_t'        : safestrptime,
            'hum_out_max'          : int,
            'hum_out_max_t'        : safestrptime,
            'temp_out_ave'         : float,
            'temp_out_min_lo'      : float,
            'temp_out_min_lo_t'    : safestrptime,
            'temp_out_min_hi'      : float,
            'temp_out_min_hi_t'    : safestrptime,
            'temp_out_min_ave'     : float,
            'temp_out_max_lo'      : float,
            'temp_out_max_lo_t'    : safestrptime,
            'temp_out_max_hi'      : float,
            'temp_out_max_hi_t'    : safestrptime,
            'temp_out_max_ave'     : float,
            'hum_in_ave'           : float,
            'hum_in_min'           : int,
            'hum_in_min_t'         : safestrptime,
            'hum_in_max'           : int,
            'hum_in_max_t'         : safestrptime,
            'temp_in_ave'          : float,
            'temp_in_min_lo'       : float,
            'temp_in_min_lo_t'     : safestrptime,
            'temp_in_min_hi'       : float,
            'temp_in_min_hi_t'     : safestrptime,
            'temp_in_min_ave'      : float,
            'temp_in_max_lo'       : float,
            'temp_in_max_lo_t'     : safestrptime,
            'temp_in_max_hi'       : float,
            'temp_in_max_hi_t'     : safestrptime,
            'temp_in_max_ave'      : float,
            'abs_pressure_ave'     : float,
            'abs_pressure_min'     : float,
            'abs_pressure_min_t'   : safestrptime,
            'abs_pressure_max'     : float,
            'abs_pressure_max_t'   : safestrptime,
            'rel_pressure_ave'     : float,
            'rel_pressure_min'     : float,
            'rel_pressure_min_t'   : safestrptime,
            'rel_pressure_max'     : float,
            'rel_pressure_max_t'   : safestrptime,
            'wind_ave'             : float,
            'wind_gust'            : float,
            'wind_gust_t'          : safestrptime,
            'wind_dir'             : int,
            'rain'                 : float,
            'rain_days'            : int,
            'illuminance_ave'      : float,
            'illuminance_max_lo'   : float,
            'illuminance_max_lo_t' : safestrptime,
            'illuminance_max_hi'   : float,
            'illuminance_max_hi_t' : safestrptime,
            'illuminance_max_ave'  : float,
            'uv_ave'               : float,
            'uv_max_lo'            : int,
            'uv_max_lo_t'          : safestrptime,
            'uv_max_hi'            : int,
            'uv_max_hi_t'          : safestrptime,
            'uv_max_ave'           : float,
            }

        def _get_cache_path(self, target_date):
            # one file per year
            path = os.path.join(self._root_dir,
                                target_date.strftime("%Y-01-01.txt"))
            lo = target_date.replace(month=1, day=1)
            if lo.year < MAXYEAR:
                hi = lo.replace(year=lo.year+1)
            else:
                hi = lo
                lo = hi.replace(year=hi.year-1)
            return path, lo, hi

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