Python django.utils.six.moves 模块，range() 实例源码

def deleted_forms(self):
        """
        Returns a list of forms that have been marked for deletion.
        """
        if not self.is_valid() or not self.can_delete:
            return []
        # construct _deleted_form_indexes which is just a list of form indexes
        # that have had their deletion widget set to True
        if not hasattr(self, '_deleted_form_indexes'):
            self._deleted_form_indexes = []
            for i in range(0, self.total_form_count()):
                form = self.forms[i]
                # if this is an extra form and hasn't changed, don't consider it
                if i >= self.initial_form_count() and not form.has_changed():
                    continue
                if self._should_delete_form(form):
                    self._deleted_form_indexes.append(i)
        return [self.forms[i] for i in self._deleted_form_indexes]

def create(self):
        # Because a cache can fail silently (e.g. memcache), we don't know if
        # we are failing to create a new session because of a key collision or
        # because the cache is missing. So we try for a (large) number of times
        # and then raise an exception. That's the risk you shoulder if using
        # cache backing.
        for i in range(10000):
            self._session_key = self._get_new_session_key()
            try:
                self.save(must_create=True)
            except CreateError:
                continue
            self.modified = True
            return
        raise RuntimeError(
            "Unable to create a new session key. "
            "It is likely that the cache is unavailable.")

def __lt__(self, other):
        olen = len(other)
        for i in range(olen):
            try:
                c = self[i] < other[i]
            except IndexError:
                # self must be shorter
                return True
            if c:
                return c
            elif other[i] < self[i]:
                return False
        return len(self) < olen

    # ### Public list interface Methods ###
    # ## Non-mutating ##

def _assign_extended_slice_rebuild(self, start, stop, step, valueList):
        'Assign an extended slice by rebuilding entire list'
        indexList = range(start, stop, step)
        # extended slice, only allow assigning slice of same size
        if len(valueList) != len(indexList):
            raise ValueError('attempt to assign sequence of size %d '
                             'to extended slice of size %d'
                             % (len(valueList), len(indexList)))

        # we're not changing the length of the sequence
        newLen = len(self)
        newVals = dict(zip(indexList, valueList))

        def newItems():
            for i in range(newLen):
                if i in newVals:
                    yield newVals[i]
                else:
                    yield self._get_single_internal(i)

        self._rebuild(newLen, newItems())

def _assign_simple_slice(self, start, stop, valueList):
        'Assign a simple slice; Can assign slice of any length'
        origLen = len(self)
        stop = max(start, stop)
        newLen = origLen - stop + start + len(valueList)

        def newItems():
            for i in range(origLen + 1):
                if i == start:
                    for val in valueList:
                        yield val

                if i < origLen:
                    if i < start or i >= stop:
                        yield self._get_single_internal(i)

        self._rebuild(newLen, newItems())

def __init__(self, num_zoom=19, tilesize=256):
        "Initializes the Google Zoom object."
        # Google's tilesize is 256x256, square tiles are assumed.
        self._tilesize = tilesize

        # The number of zoom levels
        self._nzoom = num_zoom

        # Initializing arrays to hold the parameters for each one of the
        # zoom levels.
        self._degpp = []  # Degrees per pixel
        self._radpp = []  # Radians per pixel
        self._npix = []  # 1/2 the number of pixels for a tile at the given zoom level

        # Incrementing through the zoom levels and populating the parameter arrays.
        z = tilesize  # The number of pixels per zoom level.
        for i in range(num_zoom):
            # Getting the degrees and radians per pixel, and the 1/2 the number of
            # for every zoom level.
            self._degpp.append(z / 360.)  # degrees per pixel
            self._radpp.append(z / (2 * pi))  # radians per pixel
            self._npix.append(z / 2)  # number of pixels to center of tile

            # Multiplying `z` by 2 for the next iteration.
            z *= 2

def get_zoom(self, geom):
        "Returns the optimal Zoom level for the given geometry."
        # Checking the input type.
        if not isinstance(geom, GEOSGeometry) or geom.srid != 4326:
            raise TypeError('get_zoom() expects a GEOS Geometry with an SRID of 4326.')

        # Getting the envelope for the geometry, and its associated width, height
        # and centroid.
        env = geom.envelope
        env_w, env_h = self.get_width_height(env.extent)
        center = env.centroid

        for z in range(self._nzoom):
            # Getting the tile at the zoom level.
            tile_w, tile_h = self.get_width_height(self.tile(center, z).extent)

            # When we span more than one tile, this is an approximately good
            # zoom level.
            if (env_w > tile_w) or (env_h > tile_h):
                if z == 0:
                    raise GoogleMapException('Geometry width and height should not exceed that of the Earth.')
                return z - 1

        # Otherwise, we've zoomed in to the max.
        return self._nzoom - 1

def split_parameter_list_as_sql(self, compiler, connection):
        # This is a special case for databases which limit the number of
        # elements which can appear in an 'IN' clause.
        max_in_list_size = connection.ops.max_in_list_size()
        lhs, lhs_params = self.process_lhs(compiler, connection)
        rhs, rhs_params = self.batch_process_rhs(compiler, connection)
        in_clause_elements = ['(']
        params = []
        for offset in range(0, len(rhs_params), max_in_list_size):
            if offset > 0:
                in_clause_elements.append(' OR ')
            in_clause_elements.append('%s IN (' % lhs)
            params.extend(lhs_params)
            sqls = rhs[offset: offset + max_in_list_size]
            sqls_params = rhs_params[offset: offset + max_in_list_size]
            param_group = ', '.join(sqls)
            in_clause_elements.append(param_group)
            in_clause_elements.append(')')
            params.extend(sqls_params)
        in_clause_elements.append(')')
        return ''.join(in_clause_elements), params

def get_random_string(length=12,
                      allowed_chars='abcdefghijklmnopqrstuvwxyz'
                                    'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789'):
    """
    Returns a securely generated random string.

    The default length of 12 with the a-z, A-Z, 0-9 character set returns
    a 71-bit value. log_2((26+26+10)^12) =~ 71 bits
    """
    if not using_sysrandom:
        # This is ugly, and a hack, but it makes things better than
        # the alternative of predictability. This re-seeds the PRNG
        # using a value that is hard for an attacker to predict, every
        # time a random string is required. This may change the
        # properties of the chosen random sequence slightly, but this
        # is better than absolute predictability.
        random.seed(
            hashlib.sha256(
                ("%s%s%s" % (
                    random.getstate(),
                    time.time(),
                    settings.SECRET_KEY)).encode('utf-8')
            ).digest())
    return ''.join(random.choice(allowed_chars) for i in range(length))

def deleted_forms(self):
        """
        Returns a list of forms that have been marked for deletion.
        """
        if not self.is_valid() or not self.can_delete:
            return []
        # construct _deleted_form_indexes which is just a list of form indexes
        # that have had their deletion widget set to True
        if not hasattr(self, '_deleted_form_indexes'):
            self._deleted_form_indexes = []
            for i in range(0, self.total_form_count()):
                form = self.forms[i]
                # if this is an extra form and hasn't changed, don't consider it
                if i >= self.initial_form_count() and not form.has_changed():
                    continue
                if self._should_delete_form(form):
                    self._deleted_form_indexes.append(i)
        return [self.forms[i] for i in self._deleted_form_indexes]

def create(self):
        # Because a cache can fail silently (e.g. memcache), we don't know if
        # we are failing to create a new session because of a key collision or
        # because the cache is missing. So we try for a (large) number of times
        # and then raise an exception. That's the risk you shoulder if using
        # cache backing.
        for i in range(10000):
            self._session_key = self._get_new_session_key()
            try:
                self.save(must_create=True)
            except CreateError:
                continue
            self.modified = True
            return
        raise RuntimeError(
            "Unable to create a new session key. "
            "It is likely that the cache is unavailable.")

def __lt__(self, other):
        olen = len(other)
        for i in range(olen):
            try:
                c = self[i] < other[i]
            except IndexError:
                # self must be shorter
                return True
            if c:
                return c
            elif other[i] < self[i]:
                return False
        return len(self) < olen

    # ### Public list interface Methods ###
    # ## Non-mutating ##

def _assign_extended_slice_rebuild(self, start, stop, step, valueList):
        'Assign an extended slice by rebuilding entire list'
        indexList = range(start, stop, step)
        # extended slice, only allow assigning slice of same size
        if len(valueList) != len(indexList):
            raise ValueError('attempt to assign sequence of size %d '
                             'to extended slice of size %d'
                             % (len(valueList), len(indexList)))

        # we're not changing the length of the sequence
        newLen = len(self)
        newVals = dict(zip(indexList, valueList))

        def newItems():
            for i in range(newLen):
                if i in newVals:
                    yield newVals[i]
                else:
                    yield self._get_single_internal(i)

        self._rebuild(newLen, newItems())

def _assign_simple_slice(self, start, stop, valueList):
        'Assign a simple slice; Can assign slice of any length'
        origLen = len(self)
        stop = max(start, stop)
        newLen = origLen - stop + start + len(valueList)

        def newItems():
            for i in range(origLen + 1):
                if i == start:
                    for val in valueList:
                        yield val

                if i < origLen:
                    if i < start or i >= stop:
                        yield self._get_single_internal(i)

        self._rebuild(newLen, newItems())

def __init__(self, num_zoom=19, tilesize=256):
        "Initializes the Google Zoom object."
        # Google's tilesize is 256x256, square tiles are assumed.
        self._tilesize = tilesize

        # The number of zoom levels
        self._nzoom = num_zoom

        # Initializing arrays to hold the parameters for each one of the
        # zoom levels.
        self._degpp = []  # Degrees per pixel
        self._radpp = []  # Radians per pixel
        self._npix = []  # 1/2 the number of pixels for a tile at the given zoom level

        # Incrementing through the zoom levels and populating the parameter arrays.
        z = tilesize  # The number of pixels per zoom level.
        for i in range(num_zoom):
            # Getting the degrees and radians per pixel, and the 1/2 the number of
            # for every zoom level.
            self._degpp.append(z / 360.)  # degrees per pixel
            self._radpp.append(z / (2 * pi))  # radians per pixel
            self._npix.append(z / 2)  # number of pixels to center of tile

            # Multiplying `z` by 2 for the next iteration.
            z *= 2

def get_zoom(self, geom):
        "Returns the optimal Zoom level for the given geometry."
        # Checking the input type.
        if not isinstance(geom, GEOSGeometry) or geom.srid != 4326:
            raise TypeError('get_zoom() expects a GEOS Geometry with an SRID of 4326.')

        # Getting the envelope for the geometry, and its associated width, height
        # and centroid.
        env = geom.envelope
        env_w, env_h = self.get_width_height(env.extent)
        center = env.centroid

        for z in range(self._nzoom):
            # Getting the tile at the zoom level.
            tile_w, tile_h = self.get_width_height(self.tile(center, z).extent)

            # When we span more than one tile, this is an approximately good
            # zoom level.
            if (env_w > tile_w) or (env_h > tile_h):
                if z == 0:
                    raise GoogleMapException('Geometry width and height should not exceed that of the Earth.')
                return z - 1

        # Otherwise, we've zoomed in to the max.
        return self._nzoom - 1

def deleted_forms(self):
        """
        Returns a list of forms that have been marked for deletion.
        """
        if not self.is_valid() or not self.can_delete:
            return []
        # construct _deleted_form_indexes which is just a list of form indexes
        # that have had their deletion widget set to True
        if not hasattr(self, '_deleted_form_indexes'):
            self._deleted_form_indexes = []
            for i in range(0, self.total_form_count()):
                form = self.forms[i]
                # if this is an extra form and hasn't changed, don't consider it
                if i >= self.initial_form_count() and not form.has_changed():
                    continue
                if self._should_delete_form(form):
                    self._deleted_form_indexes.append(i)
        return [self.forms[i] for i in self._deleted_form_indexes]

def create(self):
        # Because a cache can fail silently (e.g. memcache), we don't know if
        # we are failing to create a new session because of a key collision or
        # because the cache is missing. So we try for a (large) number of times
        # and then raise an exception. That's the risk you shoulder if using
        # cache backing.
        for i in range(10000):
            self._session_key = self._get_new_session_key()
            try:
                self.save(must_create=True)
            except CreateError:
                continue
            self.modified = True
            return
        raise RuntimeError(
            "Unable to create a new session key. "
            "It is likely that the cache is unavailable.")

def stored_name(self, name):
        cleaned_name = self.clean_name(name)
        hash_key = self.hash_key(cleaned_name)
        cache_name = self.hashed_files.get(hash_key)
        if cache_name:
            return cache_name
        # No cached name found, recalculate it from the files.
        intermediate_name = name
        for i in range(self.max_post_process_passes + 1):
            cache_name = self.clean_name(
                self.hashed_name(name, content=None, filename=intermediate_name)
            )
            if intermediate_name == cache_name:
                # Store the hashed name if there was a miss.
                self.hashed_files[hash_key] = cache_name
                return cache_name
            else:
                # Move on to the next intermediate file.
                intermediate_name = cache_name
        # If the cache name can't be determined after the max number of passes,
        # the intermediate files on disk may be corrupt; avoid an infinite loop.
        raise ValueError("The name '%s' could not be hashed with %r." % (name, self))

def __delitem__(self, index):
        "Delete the item(s) at the specified index/slice."
        if not isinstance(index, six.integer_types + (slice,)):
            raise TypeError("%s is not a legal index" % index)

        # calculate new length and dimensions
        origLen = len(self)
        if isinstance(index, six.integer_types):
            index = self._checkindex(index)
            indexRange = [index]
        else:
            indexRange = range(*index.indices(origLen))

        newLen = origLen - len(indexRange)
        newItems = (self._get_single_internal(i)
                    for i in range(origLen)
                    if i not in indexRange)

        self._rebuild(newLen, newItems)

def __lt__(self, other):
        olen = len(other)
        for i in range(olen):
            try:
                c = self[i] < other[i]
            except IndexError:
                # self must be shorter
                return True
            if c:
                return c
            elif other[i] < self[i]:
                return False
        return len(self) < olen

    # ### Public list interface Methods ###
    # ## Non-mutating ##

def _assign_extended_slice_rebuild(self, start, stop, step, valueList):
        'Assign an extended slice by rebuilding entire list'
        indexList = range(start, stop, step)
        # extended slice, only allow assigning slice of same size
        if len(valueList) != len(indexList):
            raise ValueError('attempt to assign sequence of size %d '
                             'to extended slice of size %d'
                             % (len(valueList), len(indexList)))

        # we're not changing the length of the sequence
        newLen = len(self)
        newVals = dict(zip(indexList, valueList))

        def newItems():
            for i in range(newLen):
                if i in newVals:
                    yield newVals[i]
                else:
                    yield self._get_single_internal(i)

        self._rebuild(newLen, newItems())

def _assign_simple_slice(self, start, stop, valueList):
        'Assign a simple slice; Can assign slice of any length'
        origLen = len(self)
        stop = max(start, stop)
        newLen = origLen - stop + start + len(valueList)

        def newItems():
            for i in range(origLen + 1):
                if i == start:
                    for val in valueList:
                        yield val

                if i < origLen:
                    if i < start or i >= stop:
                        yield self._get_single_internal(i)

        self._rebuild(newLen, newItems())

def deleted_forms(self):
        """
        Returns a list of forms that have been marked for deletion.
        """
        if not self.is_valid() or not self.can_delete:
            return []
        # construct _deleted_form_indexes which is just a list of form indexes
        # that have had their deletion widget set to True
        if not hasattr(self, '_deleted_form_indexes'):
            self._deleted_form_indexes = []
            for i in range(0, self.total_form_count()):
                form = self.forms[i]
                # if this is an extra form and hasn't changed, don't consider it
                if i >= self.initial_form_count() and not form.has_changed():
                    continue
                if self._should_delete_form(form):
                    self._deleted_form_indexes.append(i)
        return [self.forms[i] for i in self._deleted_form_indexes]

def create(self):
        # Because a cache can fail silently (e.g. memcache), we don't know if
        # we are failing to create a new session because of a key collision or
        # because the cache is missing. So we try for a (large) number of times
        # and then raise an exception. That's the risk you shoulder if using
        # cache backing.
        for i in range(10000):
            self._session_key = self._get_new_session_key()
            try:
                self.save(must_create=True)
            except CreateError:
                continue
            self.modified = True
            return
        raise RuntimeError(
            "Unable to create a new session key. "
            "It is likely that the cache is unavailable.")

def stored_name(self, name):
        cleaned_name = self.clean_name(name)
        hash_key = self.hash_key(cleaned_name)
        cache_name = self.hashed_files.get(hash_key)
        if cache_name:
            return cache_name
        # No cached name found, recalculate it from the files.
        intermediate_name = name
        for i in range(self.max_post_process_passes + 1):
            cache_name = self.clean_name(
                self.hashed_name(name, content=None, filename=intermediate_name)
            )
            if intermediate_name == cache_name:
                # Store the hashed name if there was a miss.
                self.hashed_files[hash_key] = cache_name
                return cache_name
            else:
                # Move on to the next intermediate file.
                intermediate_name = cache_name
        # If the cache name can't be determined after the max number of passes,
        # the intermediate files on disk may be corrupt; avoid an infinite loop.
        raise ValueError("The name '%s' could not be hashed with %r." % (name, self))

def __delitem__(self, index):
        "Delete the item(s) at the specified index/slice."
        if not isinstance(index, six.integer_types + (slice,)):
            raise TypeError("%s is not a legal index" % index)

        # calculate new length and dimensions
        origLen = len(self)
        if isinstance(index, six.integer_types):
            index = self._checkindex(index)
            indexRange = [index]
        else:
            indexRange = range(*index.indices(origLen))

        newLen = origLen - len(indexRange)
        newItems = (self._get_single_internal(i)
                    for i in range(origLen)
                    if i not in indexRange)

        self._rebuild(newLen, newItems)

def __lt__(self, other):
        olen = len(other)
        for i in range(olen):
            try:
                c = self[i] < other[i]
            except IndexError:
                # self must be shorter
                return True
            if c:
                return c
            elif other[i] < self[i]:
                return False
        return len(self) < olen

    # ### Public list interface Methods ###
    # ## Non-mutating ##

def _assign_extended_slice_rebuild(self, start, stop, step, valueList):
        'Assign an extended slice by rebuilding entire list'
        indexList = range(start, stop, step)
        # extended slice, only allow assigning slice of same size
        if len(valueList) != len(indexList):
            raise ValueError('attempt to assign sequence of size %d '
                             'to extended slice of size %d'
                             % (len(valueList), len(indexList)))

        # we're not changing the length of the sequence
        newLen = len(self)
        newVals = dict(zip(indexList, valueList))

        def newItems():
            for i in range(newLen):
                if i in newVals:
                    yield newVals[i]
                else:
                    yield self._get_single_internal(i)

        self._rebuild(newLen, newItems())

def _assign_simple_slice(self, start, stop, valueList):
        'Assign a simple slice; Can assign slice of any length'
        origLen = len(self)
        stop = max(start, stop)
        newLen = origLen - stop + start + len(valueList)

        def newItems():
            for i in range(origLen + 1):
                if i == start:
                    for val in valueList:
                        yield val

                if i < origLen:
                    if i < start or i >= stop:
                        yield self._get_single_internal(i)

        self._rebuild(newLen, newItems())

def __init__(self, attrs=None, years=None, months=None, empty_label=None):
        self.attrs = attrs or {}

        # Optional list or tuple of years to use in the "year" select box.
        if years:
            self.years = years
        else:
            this_year = datetime.date.today().year
            self.years = range(this_year, this_year + 10)

        # Optional dict of months to use in the "month" select box.
        if months:
            self.months = months
        else:
            self.months = MONTHS

        # Optional string, list, or tuple to use as empty_label.
        if isinstance(empty_label, (list, tuple)):
            if not len(empty_label) == 3:
                raise ValueError('empty_label list/tuple must have 3 elements.')

            self.year_none_value = (0, empty_label[0])
            self.month_none_value = (0, empty_label[1])
            self.day_none_value = (0, empty_label[2])
        else:
            if empty_label is not None:
                self.none_value = (0, empty_label)

            self.year_none_value = self.none_value
            self.month_none_value = self.none_value
            self.day_none_value = self.none_value

def render(self, name, value, attrs=None):
        try:
            year_val, month_val, day_val = value.year, value.month, value.day
        except AttributeError:
            year_val = month_val = day_val = None
            if isinstance(value, six.string_types):
                if settings.USE_L10N:
                    try:
                        input_format = get_format('DATE_INPUT_FORMATS')[0]
                        v = datetime.datetime.strptime(force_str(value), input_format)
                        year_val, month_val, day_val = v.year, v.month, v.day
                    except ValueError:
                        pass
                if year_val is None:
                    match = self.date_re.match(value)
                    if match:
                        year_val, month_val, day_val = [int(val) for val in match.groups()]
        html = {}
        choices = [(i, i) for i in self.years]
        html['year'] = self.create_select(name, self.year_field, value, year_val, choices, self.year_none_value)
        choices = list(self.months.items())
        html['month'] = self.create_select(name, self.month_field, value, month_val, choices, self.month_none_value)
        choices = [(i, i) for i in range(1, 32)]
        html['day'] = self.create_select(name, self.day_field, value, day_val, choices, self.day_none_value)

        output = []
        for field in self._parse_date_fmt():
            output.append(html[field])
        return mark_safe('\n'.join(output))

def forms(self):
        """
        Instantiate forms at first property access.
        """
        # DoS protection is included in total_form_count()
        forms = [self._construct_form(i, **self.get_form_kwargs(i))
                 for i in range(self.total_form_count())]
        return forms

def ordered_forms(self):
        """
        Returns a list of form in the order specified by the incoming data.
        Raises an AttributeError if ordering is not allowed.
        """
        if not self.is_valid() or not self.can_order:
            raise AttributeError("'%s' object has no attribute 'ordered_forms'" % self.__class__.__name__)
        # Construct _ordering, which is a list of (form_index, order_field_value)
        # tuples. After constructing this list, we'll sort it by order_field_value
        # so we have a way to get to the form indexes in the order specified
        # by the form data.
        if not hasattr(self, '_ordering'):
            self._ordering = []
            for i in range(0, self.total_form_count()):
                form = self.forms[i]
                # if this is an extra form and hasn't changed, don't consider it
                if i >= self.initial_form_count() and not form.has_changed():
                    continue
                # don't add data marked for deletion to self.ordered_data
                if self.can_delete and self._should_delete_form(form):
                    continue
                self._ordering.append((i, form.cleaned_data[ORDERING_FIELD_NAME]))
            # After we're done populating self._ordering, sort it.
            # A sort function to order things numerically ascending, but
            # None should be sorted below anything else. Allowing None as
            # a comparison value makes it so we can leave ordering fields
            # blank.

            def compare_ordering_key(k):
                if k[1] is None:
                    return (1, 0)  # +infinity, larger than any number
                return (0, k[1])
            self._ordering.sort(key=compare_ordering_key)
        # Return a list of form.cleaned_data dicts in the order specified by
        # the form data.
        return [self.forms[i[0]] for i in self._ordering]

def full_clean(self):
        """
        Cleans all of self.data and populates self._errors and
        self._non_form_errors.
        """
        self._errors = []
        self._non_form_errors = self.error_class()

        if not self.is_bound:  # Stop further processing.
            return
        for i in range(0, self.total_form_count()):
            form = self.forms[i]
            self._errors.append(form.errors)
        try:
            if (self.validate_max and
                    self.total_form_count() - len(self.deleted_forms) > self.max_num) or \
                    self.management_form.cleaned_data[TOTAL_FORM_COUNT] > self.absolute_max:
                raise ValidationError(ungettext(
                    "Please submit %d or fewer forms.",
                    "Please submit %d or fewer forms.", self.max_num) % self.max_num,
                    code='too_many_forms',
                )
            if (self.validate_min and
                    self.total_form_count() - len(self.deleted_forms) < self.min_num):
                raise ValidationError(ungettext(
                    "Please submit %d or more forms.",
                    "Please submit %d or more forms.", self.min_num) % self.min_num,
                    code='too_few_forms')
            # Give self.clean() a chance to do cross-form validation.
            self.clean()
        except ValidationError as e:
            self._non_form_errors = self.error_class(e.error_list)

def _fix_polygon(self, poly):
        # Fix single polygon orientation as described in __init__()
        if self._isClockwise(poly.exterior_ring):
            poly.exterior_ring = list(reversed(poly.exterior_ring))

        for i in range(1, len(poly)):
            if not self._isClockwise(poly[i]):
                poly[i] = list(reversed(poly[i]))

        return poly

def _isClockwise(self, coords):
        # A modified shoelace algorithm to determine polygon orientation.
        # See https://en.wikipedia.org/wiki/Shoelace_formula
        n = len(coords)
        area = 0.0
        for i in range(n):
            j = (i + 1) % n
            area += coords[i][0] * coords[j][1]
            area -= coords[j][0] * coords[i][1]
        return area < 0.0

def __getitem__(self, index):
        "Gets the Feature at the specified index."
        if isinstance(index, six.integer_types):
            # An integer index was given -- we cannot do a check based on the
            # number of features because the beginning and ending feature IDs
            # are not guaranteed to be 0 and len(layer)-1, respectively.
            if index < 0:
                raise OGRIndexError('Negative indices are not allowed on OGR Layers.')
            return self._make_feature(index)
        elif isinstance(index, slice):
            # A slice was given
            start, stop, stride = index.indices(self.num_feat)
            return [self._make_feature(fid) for fid in range(start, stop, stride)]
        else:
            raise TypeError('Integers and slices may only be used when indexing OGR Layers.')

def fields(self):
        """
        Returns a list of string names corresponding to each of the Fields
        available in this Layer.
        """
        return [force_text(capi.get_field_name(capi.get_field_defn(self._ldefn, i)),
                           self._ds.encoding, strings_only=True)
                for i in range(self.num_fields)]

def field_types(self):
        """
        Returns a list of the types of fields in this Layer.  For example,
        the list [OFTInteger, OFTReal, OFTString] would be returned for
        an OGR layer that had an integer, a floating-point, and string
        fields.
        """
        return [OGRFieldTypes[capi.get_field_type(capi.get_field_defn(self._ldefn, i))]
                for i in range(self.num_fields)]

def field_widths(self):
        "Returns a list of the maximum field widths for the features."
        return [capi.get_field_width(capi.get_field_defn(self._ldefn, i))
                for i in range(self.num_fields)]

def field_precisions(self):
        "Returns the field precisions for the features."
        return [capi.get_field_precision(capi.get_field_defn(self._ldefn, i))
                for i in range(self.num_fields)]

def __getitem__(self, index):
        """
        Gets the Field object at the specified index, which may be either
        an integer or the Field's string label.  Note that the Field object
        is not the field's _value_ -- use the `get` method instead to
        retrieve the value (e.g. an integer) instead of a Field instance.
        """
        if isinstance(index, six.string_types):
            i = self.index(index)
        else:
            if index < 0 or index > self.num_fields:
                raise OGRIndexError('index out of range')
            i = index
        return Field(self, i)

def fields(self):
        "Returns a list of fields in the Feature."
        return [capi.get_field_name(capi.get_field_defn(self._layer._ldefn, i))
                for i in range(self.num_fields)]

def __iter__(self):
        for idx in range(1, len(self) + 1):
            yield GDALBand(self.source, idx)

def __getitem__(self, index):
        "Returns the Point at the given index."
        if index >= 0 and index < self.point_count:
            x, y, z = c_double(), c_double(), c_double()
            capi.get_point(self.ptr, index, byref(x), byref(y), byref(z))
            dim = self.coord_dim
            if dim == 1:
                return (x.value,)
            elif dim == 2:
                return (x.value, y.value)
            elif dim == 3:
                return (x.value, y.value, z.value)
        else:
            raise OGRIndexError('index out of range: %s' % str(index))

def __iter__(self):
        "Iterates over each point in the LineString."
        for i in range(self.point_count):
            yield self[i]

def tuple(self):
        "Returns the tuple representation of this LineString."
        return tuple(self[i] for i in range(len(self)))

def __iter__(self):
        "Iterates through each ring in the Polygon."
        for i in range(self.geom_count):
            yield self[i]

def __getitem__(self, index):
        "Gets the ring at the specified index."
        if index < 0 or index >= self.geom_count:
            raise OGRIndexError('index out of range: %s' % index)
        else:
            return OGRGeometry(capi.clone_geom(capi.get_geom_ref(self.ptr, index)), self.srs)

    # Polygon Properties