# (C) British Crown Copyright 2011 - 2012, Met Office
#
# This file is part of cartopy.
#
# cartopy is free software: you can redistribute it and/or modify it under
# the terms of the GNU Lesser General Public License as published by the
# Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# cartopy 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 Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with cartopy. If not, see <http://www.gnu.org/licenses/>.
"""
Provides a collection of sub-packages for loading, saving and retrieving
various data formats.
"""
import os
import string
import urllib2
import warnings
from cartopy import config
def fh_getter(fh, mode='r', needs_filename=False):
"""
Convenience function for opening files.
Args:
* fh - File handle, filename or (file handle, filename) tuple
Kwargs:
* mode - Open mode. Defaults to "r".
Returns:
* (file handle, filename), opened in the given mode.
"""
if mode != 'r':
raise ValueError('Only mode "r" currently supported.')
if isinstance(fh, basestring):
filename = fh
fh = open(fh, mode)
elif isinstance(fh, tuple):
fh, filename = fh
if filename is None:
try:
filename = fh.name
except AttributeError: # does this occur?
if needs_filename:
raise ValueError('filename cannot be determined')
else:
filename = ''
return fh, filename
class DownloadWarning(Warning):
"""Issued when a file is being downloaded by a :class:`Downloader`."""
pass
[docs]class Downloader(object):
"""
Represents a resource, that can be configured easily, which knows
how to acquire itself (perhaps via HTTP).
The key interface method is :meth:`path` - typically *all* external calls
will be made to that method. To get hold of an appropriate
:class:`Downloader` instance the :func:`Downloader.from_config` static
method should be considered.
.. note:
All ``*_template`` arguments should be formattable using the
standard :meth:`string.format` rules. The formatting itself
is not done until a call to a subsequent method (such as
:meth:`Downloader.path`).
Args:
``url_template`` - The template of the full URL representing this
resource.
``target_path_template`` - The template of the full path to the file
that this Downloader represents. Typically
the path will be a subdirectory of
``config['data_dir']``, but this is not a
strict requirement. If the file does not
exist when calling :meth:`Downloader.path`
it will be downloaded to this location.
Kwargs:
``pre_downloaded_path_template`` - The template of a full path of a
file which has been downloaded
outside of this Downloader which
should be used as the file that
this resource represents. If the
file does not exist when
:meth:`Downloader.path` is called
it will not be downloaded to this
location (unlike the
``target_path_template`` argument).
"""
FORMAT_KEYS = ('config',)
"""
The minimum keys which should be provided in the ``format_dict``
argument for the ``path``, ``url``, ``target_path``,
``pre_downloaded_path`` and ``acquire_resource`` methods.
"""
def __init__(self, url_template, target_path_template,
pre_downloaded_path_template=''):
self.url_template = url_template
self.target_path_template = target_path_template
self.pre_downloaded_path_template = pre_downloaded_path_template
# define a formatter which will process the templates. Subclasses
# may override the standard ``''.format`` formatting by defining
# their own formatter subclass here.
self._formatter = string.Formatter()
[docs] def url(self, format_dict):
"""
The full URL that this resource represents.
Args:
``format_dict`` - The dictionary which is used to replace
certain template variables. Subclasses should
document which keys are expected as a minimum
in their ``FORMAT_KEYS`` class attribute.
"""
return self._formatter.format(self.url_template, **format_dict)
[docs] def target_path(self, format_dict):
"""
The path on disk of the file that this resource represents, must
either exist, or be writable by the current user. This method
does not check either of these conditions.
Args:
``format_dict`` - The dictionary which is used to replace
certain template variables. Subclasses should
document which keys are expected as a minimum
in their ``FORMAT_KEYS`` class attribute.
"""
return self._formatter.format(self.target_path_template,
**format_dict)
[docs] def pre_downloaded_path(self, format_dict):
"""
The path on disk of the file that this resource represents, if it does
not exist, then no further action will be taken with this path, and all
further processing will be done using :meth:`target_path` instead.
Args:
``format_dict`` - The dictionary which is used to replace
certain template variables. Subclasses should
document which keys are expected as a minimum
in their ``FORMAT_KEYS`` class attribute.
"""
return self._formatter.format(self.pre_downloaded_path_template,
**format_dict)
[docs] def path(self, format_dict):
"""
Returns the path to a file on disk that this resource represents.
If the file doesn't exist in :meth:`pre_downloaded_path` then it
will check whether it exists in :meth:`target_path`, otherwise
the resource will be downloaded via :meth:`acquire_resouce` from
:meth:`url` to :meth:`target_path`.
Typically, this is the method that most applications will call,
allowing implementors of new Downloaders to specialise
:meth:`acquire_resource`.
Args:
``format_dict`` - The dictionary which is used to replace
certain template variables. Subclasses should
document which keys are expected as a minimum
in their ``FORMAT_KEYS`` class attribute.
"""
pre_downloaded_path = self.pre_downloaded_path(format_dict)
target_path = self.target_path(format_dict)
if (pre_downloaded_path is not None and
os.path.exists(pre_downloaded_path)):
result_path = pre_downloaded_path
elif os.path.exists(target_path):
result_path = target_path
else:
# we need to download the file
result_path = self.acquire_resource(target_path, format_dict)
return result_path
[docs] def acquire_resource(self, target_path, format_dict):
"""
Downloads, via HTTP, the file that this resource represents.
Subclasses will typically override this method.
Args:
``format_dict`` - The dictionary which is used to replace
certain template variables. Subclasses should
document which keys are expected as a minimum
in their ``FORMAT_KEYS`` class attribute.
"""
target_dir = os.path.dirname(target_path)
if not os.path.isdir(target_dir):
os.makedirs(target_dir)
url = self.url(format_dict)
# try getting the resource (no exception handling, just let it raise)
response = self._urlopen(url)
with open(target_path, 'wb') as fh:
fh.write(response.read())
return target_path
def _urlopen(self, url):
"""
Return a file handle to the given HTTP resource URL.
Caller should close the file handle when finished with it.
"""
warnings.warn('Downloading: {}'.format(url), DownloadWarning)
return urllib2.urlopen(url)
@staticmethod
[docs] def from_config(specification, config_dict=None):
"""
The ``from_config`` static method implements the logic for acquiring a
Downloader (sub)class instance from the config dictionary.
Args:
``specification`` - should be iterable, as it will be traversed
in reverse order to find the most appropriate
Downloader instance for this specification.
An example specification is
``('shapefiles', 'natural_earth')`` for the
Natural Earth shapefiles.
Kwargs:
``config_dict`` - typically this is left as None to use the
default ``cartopy.config`` "downloaders"
dictionary.
Example:
>>> from cartopy.io import Downloader
>>>
>>> dnldr = Downloader('http://example.com/{name}', './{name}.txt')
>>> config = {('level_1', 'level_2'): dnldr}
>>> d1 = Downloader.from_config(('level_1', 'level_2', 'level_3'),
... config_dict=config)
>>> print d1.url_template
http://example.com/{name}
>>> print d1.url({'name': 'item_name'})
http://example.com/item_name
"""
spec_depth = len(specification)
if config_dict is None:
downloaders = config['downloaders']
else:
downloaders = config_dict
result_downloader = None
for i in range(spec_depth, 0, -1):
lookup = specification[:i]
downloadable_item = downloaders.get(lookup, None)
if downloadable_item is not None:
result_downloader = downloadable_item
break
if result_downloader is None:
# should never really happen, but could if the user does
# some strange things like not having any downloaders defined
# in the config...
raise ValueError('No generic downloadable item in the config '
'dictionary for {}'.format(specification))
return result_downloader
