Source code for yt.data_objects.static_output

Dataset and related data structures.


# Copyright (c) 2013, yt Development Team.
# Distributed under the terms of the Modified BSD License.
# The full license is in the file COPYING.txt, distributed with this software.

import functools
import itertools
import numpy as np
import os
import time
import weakref
import warnings

from collections import defaultdict
from yt.extern.six import add_metaclass, string_types

from yt.config import ytcfg
from yt.fields.derived_field import \
from yt.funcs import \
    mylog, \
    set_intersection, \
from yt.utilities.cosmology import \
from yt.utilities.exceptions import \
    YTObjectNotImplemented, \
    YTFieldNotFound, \
    YTGeometryNotSupported, \
from yt.utilities.parallel_tools.parallel_analysis_interface import \
from yt.utilities.parameter_file_storage import \
    ParameterFileStore, \
    NoParameterShelf, \
from yt.units.dimensions import current_mks
from yt.units.unit_object import Unit, unit_system_registry, \
from yt.units.unit_registry import UnitRegistry
from yt.fields.derived_field import \
from yt.fields.fluid_fields import \
from yt.fields.particle_fields import \
from yt.data_objects.particle_filters import \
from yt.data_objects.particle_unions import \
from yt.data_objects.data_containers import \
from yt.utilities.minimal_representation import \
from yt.units.yt_array import \
    YTArray, \
from yt.units.unit_systems import create_code_unit_system
from yt.data_objects.region_expression import \
from yt.geometry.coordinates.api import \
    CoordinateHandler, \
    CartesianCoordinateHandler, \
    PolarCoordinateHandler, \
    CylindricalCoordinateHandler, \
    SphericalCoordinateHandler, \
    GeographicCoordinateHandler, \
    SpectralCubeCoordinateHandler, \

# We want to support the movie format in the future.
# When such a thing comes to pass, I'll move all the stuff that is contant up
# to here, and then have it instantiate EnzoDatasets as appropriate.

_cached_datasets = weakref.WeakValueDictionary()
_ds_store = ParameterFileStore()

def _unsupported_object(ds, obj_name):
    def _raise_unsupp(*args, **kwargs):
        raise YTObjectNotImplemented(ds, obj_name)
    return _raise_unsupp

class RegisteredDataset(type):
    def __init__(cls, name, b, d):
        type.__init__(cls, name, b, d)
        output_type_registry[name] = cls
        mylog.debug("Registering: %s as %s", name, cls)

class FieldTypeContainer(object):
    def __init__(self, ds):
        self.ds = weakref.proxy(ds)

    def __getattr__(self, attr):
        ds = self.__getattribute__('ds')
        fnc = FieldNameContainer(ds, attr)
        if len(dir(fnc)) == 0:
            return self.__getattribute__(attr)
        return fnc

    _field_types = None
    def field_types(self):
        if self._field_types is None:
            self._field_types = set(t for t, n in self.ds.field_info)
        return self._field_types

    def __dir__(self):
        return list(self.field_types)

    def __iter__(self):
        for ft in self.field_types:
            fnc = FieldNameContainer(self.ds, ft)
            if len(dir(fnc)) == 0:
                yield self.__getattribute__(ft)
                yield fnc

    def __contains__(self, obj):
        ob = None
        if isinstance(obj, FieldNameContainer):
            ob = obj.field_type
        elif isinstance(obj, string_types):
            ob = obj

        return ob in self.field_types

class FieldNameContainer(object):
    def __init__(self, ds, field_type):
        self.ds = ds
        self.field_type = field_type

    def __getattr__(self, attr):
        ft = self.__getattribute__("field_type")
        ds = self.__getattribute__("ds")
        if (ft, attr) not in ds.field_info:
            return self.__getattribute__(attr)
        return ds.field_info[ft, attr]

    def __dir__(self):
        return [n for t, n in self.ds.field_info
                if t == self.field_type]

    def __iter__(self):
        for t, n in self.ds.field_info:
            if t == self.field_type:
                yield self.ds.field_info[t, n]

    def __contains__(self, obj):
        if isinstance(obj, DerivedField):
            if self.field_type ==[0] and in self.ds.field_info:
                # e.g. from a completely different dataset
                if self.ds.field_info[] is not obj:
                    return False
                return True
        elif isinstance(obj, tuple):
            if self.field_type == obj[0] and obj in self.ds.field_info:
                return True
        elif isinstance(obj, string_types):
            if (self.field_type, obj) in self.ds.field_info:
                return True
        return False

class IndexProxy(object):
    # This is a simple proxy for Index objects.  It enables backwards
    # compatibility so that operations like .h.sphere, .h.print_stats and
    # .h.grid_left_edge will correctly pass through to the various dataset or
    # index objects.
    def __init__(self, ds):
        self.ds = weakref.proxy(ds)

    def __getattr__(self, name):
        # Check the ds first
        if hasattr(self.ds, name):
            return getattr(self.ds, name)
        # Now for a subset of the available items, check the ds.index.
        elif name in self.ds.index._index_properties:
            return getattr(self.ds.index, name)
        raise AttributeError

class MutableAttribute(object):
    """A descriptor for mutable data"""
    def __init__(self): = weakref.WeakKeyDictionary()

    def __get__(self, instance, owner):
        if not instance:
            return None
        ret =, None)
            ret = ret.copy()
        except AttributeError:
        return ret

    def __set__(self, instance, value):[instance] = value

def requires_index(attr_name):
    def ireq(self):
        # By now it should have been set
        attr = self.__dict__[attr_name]
        return attr

    def ireq(self, value):
        self.__dict__[attr_name] = value

    return ireq

class Dataset(object):

    default_fluid_type = "gas"
    default_field = ("gas", "density")
    fluid_types = ("gas", "deposit", "index")
    particle_types = ("io",) # By default we have an 'all'
    particle_types_raw = ("io",)
    geometry = "cartesian"
    coordinates = None
    storage_filename = None
    particle_unions = None
    known_filters = None
    _index_class = None
    field_units = None
    derived_field_list = requires_index("derived_field_list")
    fields = requires_index("fields")
    _instantiated = False
    _particle_type_counts = None

    def __new__(cls, filename=None, *args, **kwargs):
        if not isinstance(filename, string_types):
            obj = object.__new__(cls)
            # The Stream frontend uses a StreamHandler object to pass metadata
            # to __init__.
            is_stream = (hasattr(filename, 'get_fields') and
                         hasattr(filename, 'get_particle_type'))
            if not is_stream:
                obj.__init__(filename, *args, **kwargs)
            return obj
        apath = os.path.abspath(filename)
        if ytcfg.getboolean("yt","skip_dataset_cache"):
            obj = object.__new__(cls)
        elif apath not in _cached_datasets:
            obj = object.__new__(cls)
            if obj._skip_cache is False:
                _cached_datasets[apath] = obj
            obj = _cached_datasets[apath]
        return obj

    def __init__(self, filename, dataset_type=None, file_style=None,
                 units_override=None, unit_system="cgs"):
        Base class for generating new output types.  Principally consists of
        a *filename* and a *dataset_type* which will be passed on to children.
        # We return early and do NOT initialize a second time if this file has
        # already been initialized.
        if self._instantiated: return
        self.dataset_type = dataset_type
        self.file_style = file_style
        self.conversion_factors = {}
        self.parameters = {}
        self.region_expression = self.r = RegionExpression(self)
        self.known_filters = self.known_filters or {}
        self.particle_unions = self.particle_unions or {}
        self.field_units = self.field_units or {}
        if units_override is None:
            units_override = {}
        self.units_override = units_override

        # path stuff
        self.parameter_filename = str(filename)
        self.basename = os.path.basename(filename) = os.path.expanduser(os.path.dirname(filename))
        self.fullpath = os.path.abspath(
        self.backup_filename = self.parameter_filename + '_backup.gdf'
        self.read_from_backup = False
        if os.path.exists(self.backup_filename):
            self.read_from_backup = True
        if len( == 0:
   = "."

        # to get the timing right, do this before the heavy lifting
        self._instantiated = time.time()

        self.min_level = 0
        self.no_cgs_equiv_length = False



        # Because we need an instantiated class to check the ds's existence in
        # the cache, we move that check to here from __new__.  This avoids
        # double-instantiation.
        except NoParameterShelf:


    def _set_derived_attrs(self):
        if self.domain_left_edge is None or self.domain_right_edge is None:
            self.domain_center = np.zeros(3)
            self.domain_width = np.zeros(3)
            self.domain_center = 0.5 * (self.domain_right_edge + self.domain_left_edge)
            self.domain_width = self.domain_right_edge - self.domain_left_edge
        if not isinstance(self.current_time, YTQuantity):
            self.current_time = self.quan(self.current_time, "code_time")
        for attr in ("center", "width", "left_edge", "right_edge"):
            n = "domain_%s" % attr
            v = getattr(self, n)
            if not isinstance(v, YTArray):
                v = self.arr(v, "code_length")
                setattr(self, n, v)

    def __reduce__(self):
        args = (self._hash(),)
        return (_reconstruct_ds, args)

    def __repr__(self):
        return self.basename

    def _hash(self):
        s = "%s;%s;%s" % (self.basename,
            self.current_time, self.unique_identifier)
            import hashlib
            return hashlib.md5(s.encode('utf-8')).hexdigest()
        except ImportError:
            return s.replace(";", "*")
    _checksum = None
    def checksum(self):
        Computes md5 sum of a dataset.

        Note: Currently this property is unable to determine a complete set of
        files that are a part of a given dataset. As a first approximation, the
        checksum of :py:attr:`~parameter_file` is calculated. In case
        :py:attr:`~parameter_file` is a directory, checksum of all files inside
        the directory is calculated.
        if self._checksum is None:
                import hashlib
            except ImportError:
                self._checksum = 'nohashlib'
                return self._checksum

            def generate_file_md5(m, filename, blocksize=2**20):
                with open(filename , "rb") as f:
                    while True:
                        buf =
                        if not buf:

            m = hashlib.md5()
            if os.path.isdir(self.parameter_filename):
                for root, _, files in os.walk(self.parameter_filename):
                    for fname in files:
                        fname = os.path.join(root, fname)
                        generate_file_md5(m, fname)
            elif os.path.isfile(self.parameter_filename):
                generate_file_md5(m, self.parameter_filename)
                m = 'notafile'

            if hasattr(m, 'hexdigest'):
                m = m.hexdigest()
            self._checksum = m
        return self._checksum

    domain_left_edge = MutableAttribute()
    domain_right_edge = MutableAttribute()
    domain_width = MutableAttribute()
    domain_dimensions = MutableAttribute()
    domain_center = MutableAttribute()

    def _mrep(self):
        return MinimalDataset(self)

    def _skip_cache(self):
        return False

    def hub_upload(self):

    def _is_valid(cls, *args, **kwargs):
        return False

    def _guess_candidates(cls, base, directories, files):
        This is a class method that accepts a directory (base), a list of files
        in that directory, and a list of subdirectories.  It should return a
        list of filenames (defined relative to the supplied directory) and a
        boolean as to whether or not further directories should be recursed.

        This function doesn't need to catch all possibilities, nor does it need
        to filter possibilities.
        return [], True

    def close(self):

    def __getitem__(self, key):
        """ Returns units, parameters, or conversion_factors in that order. """
        return self.parameters[key]

    def __iter__(self):
      for i in self.parameters: yield i

    def get_smallest_appropriate_unit(self, v, quantity='distance',
        Returns the largest whole unit smaller than the YTQuantity passed to
        it as a string.

        The quantity keyword can be equal to `distance` or `time`.  In the
        case of distance, the units are: 'Mpc', 'kpc', 'pc', 'au', 'rsun',
        'km', etc.  For time, the units are: 'Myr', 'kyr', 'yr', 'day', 'hr',
        's', 'ms', etc.

        If return_quantity is set to True, it finds the largest YTQuantity
        object with a whole unit and a power of ten as the coefficient, and it
        returns this YTQuantity.
        good_u = None
        if quantity == 'distance':
            unit_list =['Ppc', 'Tpc', 'Gpc', 'Mpc', 'kpc', 'pc', 'au', 'rsun',
                        'km', 'cm', 'um', 'nm', 'pm']
        elif quantity == 'time':
            unit_list =['Yyr', 'Zyr', 'Eyr', 'Pyr', 'Tyr', 'Gyr', 'Myr', 'kyr',
                        'yr', 'day', 'hr', 's', 'ms', 'us', 'ns', 'ps', 'fs']
            raise SyntaxError("Specified quantity must be equal to 'distance'"\
                              "or 'time'.")
        for unit in unit_list:
            uq = self.quan(1.0, unit)
            if uq <= v:
                good_u = unit
        if good_u is None and quantity == 'distance': good_u = 'cm'
        if good_u is None and quantity == 'time': good_u = 's'
        if return_quantity:
            unit_index = unit_list.index(good_u)
            # This avoids indexing errors
            if unit_index == 0: return self.quan(1, unit_list[0])
            # Number of orders of magnitude between unit and next one up
            OOMs = np.ceil(np.log10(self.quan(1, unit_list[unit_index-1]) /
                                    self.quan(1, unit_list[unit_index])))
            # Backwards order of coefficients (e.g. [100, 10, 1])
            coeffs = 10**np.arange(OOMs)[::-1]
            for j in coeffs:
                uq = self.quan(j, good_u)
                if uq <= v:
                    return uq
            return good_u

    def has_key(self, key):
        Checks units, parameters, and conversion factors. Returns a boolean.

        return key in self.parameters

    _instantiated_index = None
    def index(self):
        if self._instantiated_index is None:
            if self._index_class is None:
                raise RuntimeError("You should not instantiate Dataset.")
            self._instantiated_index = self._index_class(
                self, dataset_type=self.dataset_type)
            # Now we do things that we need an instantiated index for
            # ...first off, we create our field_info now.
            oldsettings = np.geterr()
        return self._instantiated_index

    _index_proxy = None
    def h(self):
        if self._index_proxy is None:
            self._index_proxy = IndexProxy(self)
        return self._index_proxy
    hierarchy = h

    def print_key_parameters(self):
        for a in ["current_time", "domain_dimensions", "domain_left_edge",
                  "domain_right_edge", "cosmological_simulation"]:
            if not hasattr(self, a):
                mylog.error("Missing %s in parameter file definition!", a)
            v = getattr(self, a)
  "Parameters: %-25s = %s", a, v)
        if hasattr(self, "cosmological_simulation") and \
           getattr(self, "cosmological_simulation"):
            for a in ["current_redshift", "omega_lambda", "omega_matter",
                if not hasattr(self, a):
                    mylog.error("Missing %s in parameter file definition!", a)
                v = getattr(self, a)
      "Parameters: %-25s = %s", a, v)

    def print_stats(self):

    def field_list(self):
        return self.index.field_list

    def create_field_info(self):
        self.field_dependencies = {}
        self.derived_field_list = []
        self.filtered_particle_types = []
        self.field_info = self._field_info_class(self, self.field_list)
        for ptype in self.particle_types:
        if "all" not in self.particle_types:
            mylog.debug("Creating Particle Union 'all'")
            pu = ParticleUnion("all", list(self.particle_types_raw))
            nfields = self.add_particle_union(pu)
            if nfields == 0:
                mylog.debug("zero common fields: skipping particle union 'all'")
        mylog.debug("Loading field plugins.")
        deps, unloaded = self.field_info.check_derived_fields()
        self.fields = FieldTypeContainer(self)
        self.index.field_list = sorted(self.field_list)
        self._last_freq = (None, None)

    def setup_deprecated_fields(self):
        from yt.fields.field_aliases import _field_name_aliases
        added = []
        for old_name, new_name in _field_name_aliases:
                fi = self._get_field_info(new_name)
            except YTFieldNotFound:
            self.field_info.alias(("gas", old_name),
            added.append(("gas", old_name))

    def _setup_coordinate_handler(self):
        kwargs = {}
        if isinstance(self.geometry, tuple):
            self.geometry, ordering = self.geometry
            kwargs['ordering'] = ordering
        if isinstance(self.geometry, CoordinateHandler):
            # I kind of dislike this.  The geometry field should always be a
            # string, but the way we're set up with subclassing, we can't
            # mandate that quite the way I'd like.
            self.coordinates = self.geometry
        elif callable(self.geometry):
            cls = self.geometry
        elif self.geometry == "cartesian":
            cls = CartesianCoordinateHandler
        elif self.geometry == "cylindrical":
            cls = CylindricalCoordinateHandler
        elif self.geometry == "polar":
            cls = PolarCoordinateHandler
        elif self.geometry == "spherical":
            cls = SphericalCoordinateHandler
        elif self.geometry == "geographic":
            cls = GeographicCoordinateHandler
        elif self.geometry == "internal_geographic":
            cls = InternalGeographicCoordinateHandler
        elif self.geometry == "spectral_cube":
            cls = SpectralCubeCoordinateHandler
            raise YTGeometryNotSupported(self.geometry)
        self.coordinates = cls(self, **kwargs)

    def add_particle_union(self, union):
        # No string lookups here, we need an actual union.
        f = self.particle_fields_by_type

        # find fields common to all particle types in the union
        fields = set_intersection(
            [f[s] for s in union if s in self.particle_types_raw]

        if len(fields) == 0:
            # don't create this union if no fields are common to all
            # particle types
            return len(fields)

        for field in fields:
            units = set([])
            for s in union:
                # First we check our existing fields for units
                funits = self._get_field_info(s, field).units
                # Then we override with field_units settings.
                funits = self.field_units.get((s, field), funits)
            if len(units) == 1:
                self.field_units[, field] = list(units)[0]
        self.particle_types += (,)
        self.particle_unions[] = union
        fields = [ (, field) for field in fields]
        new_fields = [_ for _ in fields if _ not in self.field_list]
        new_field_info_fields = [
            _ for _ in fields if _ not in self.field_info.field_list]
        self.index.field_list = sorted(self.field_list)
        # Give ourselves a chance to add them here, first, then...
        # ...if we can't find them, we set them up as defaults.
        new_fields = self._setup_particle_types([])
        return len(new_fields)

    def add_particle_filter(self, filter):
        # This requires an index
        # This is a dummy, which we set up to enable passthrough of "all"
        # concatenation fields.
        n = getattr(filter, "name", filter)
        self.known_filters[n] = None
        if isinstance(filter, string_types):
            used = False
            for f in filter_registry[filter]:
                used = self._setup_filtered_type(f)
                if used:
                    filter = f
            used = self._setup_filtered_type(filter)
        if not used:
            self.known_filters.pop(n, None)
            return False
        self.known_filters[] = filter
        return True

    def _setup_filtered_type(self, filter):
        if not filter.available(self.derived_field_list):
            raise YTIllDefinedParticleFilter(
                filter, filter.missing(self.derived_field_list))
        fi = self.field_info
        fd = self.field_dependencies
        available = False
        for fn in self.derived_field_list:
            if fn[0] == filter.filtered_type:
                # Now we can add this
                available = True
                    (, fn[1]))
                fi[, fn[1]] = filter.wrap_func(fn, fi[fn])
                # Now we append the dependencies
                fd[, fn[1]] = fd[fn]
        if available:
            self.particle_types += (,)
            new_fields = self._setup_particle_types([])
            deps, _ = self.field_info.check_derived_fields(new_fields)
        return available

    def _setup_particle_types(self, ptypes = None):
        df = []
        if ptypes is None: ptypes = self.ds.particle_types_raw
        for ptype in set(ptypes):
            df += self._setup_particle_type(ptype)
        return df

    _last_freq = (None, None)
    _last_finfo = None
    def _get_field_info(self, ftype, fname = None):
        if fname is None:
            if isinstance(ftype, DerivedField):
                ftype, fname =
                ftype, fname = "unknown", ftype
        guessing_type = False
        if ftype == "unknown":
            guessing_type = True
            ftype = self._last_freq[0] or ftype
        field = (ftype, fname)
        if field == self._last_freq:
            if field not in self.field_info.field_aliases.values():
                return self._last_finfo
        if field in self.field_info:
            self._last_freq = field
            self._last_finfo = self.field_info[(ftype, fname)]
            return self._last_finfo
        if fname in self.field_info:
            # Sometimes, if guessing_type == True, this will be switched for
            # the type of field it is.  So we look at the field type and
            # determine if we need to change the type.
            fi = self._last_finfo = self.field_info[fname]
            if fi.particle_type and self._last_freq[0] \
                not in self.particle_types:
                    field = "all", field[1]
            elif not fi.particle_type and self._last_freq[0] \
                not in self.fluid_types:
                    field = self.default_fluid_type, field[1]
            self._last_freq = field
            return self._last_finfo
        # We also should check "all" for particles, which can show up if you're
        # mixing deposition/gas fields with particle fields.
        if guessing_type:
            to_guess = ["all", self.default_fluid_type] \
                     + list(self.fluid_types) \
                     + list(self.particle_types)
            for ftype in to_guess:
                if (ftype, fname) in self.field_info:
                    self._last_freq = (ftype, fname)
                    self._last_finfo = self.field_info[(ftype, fname)]
                    return self._last_finfo
        raise YTFieldNotFound((ftype, fname), self)

    def _setup_classes(self):
        # Called by subclass
        self.object_types = []
        self.objects = []
        self.plots = []
        for name, cls in sorted(data_object_registry.items()):
            if name in self._index_class._unsupported_objects:
                setattr(self, name,
                    _unsupported_object(self, name))
            cname = cls.__name__
            if cname.endswith("Base"): cname = cname[:-4]
            self._add_object_class(name, cls)
        if not np.all(self.refine_by == 2) and hasattr(self, 'proj') and \
            hasattr(self, 'overlap_proj'):
            mylog.warning("Refine by something other than two: reverting to"
                        + " overlap_proj")
            self.proj = self.overlap_proj
        if self.dimensionality < 3 and hasattr(self, 'proj') and \
            hasattr(self, 'overlap_proj'):
            mylog.warning("Dimensionality less than 3: reverting to"
                        + " overlap_proj")
            self.proj = self.overlap_proj

    def _add_object_class(self, name, base):
        obj = functools.partial(base, ds=weakref.proxy(self))
        obj.__doc__ = base.__doc__
        setattr(self, name, obj)

    def find_max(self, field):
        Returns (value, location) of the maximum of a given field.
        mylog.debug("Searching for maximum value of %s", field)
        source = self.all_data()
        max_val, mx, my, mz = \
            source.quantities.max_location(field)"Max Value is %0.5e at %0.16f %0.16f %0.16f",
              max_val, mx, my, mz)
        return max_val, self.arr([mx, my, mz], 'code_length', dtype="float64")

    def find_min(self, field):
        Returns (value, location) for the minimum of a given field.
        mylog.debug("Searching for minimum value of %s", field)
        source = self.all_data()
        min_val, mx, my, mz = \
            source.quantities.min_location(field)"Min Value is %0.5e at %0.16f %0.16f %0.16f",
              min_val, mx, my, mz)
        return min_val, self.arr([mx, my, mz], 'code_length', dtype="float64")

    def find_field_values_at_point(self, fields, coords):
        Returns the values [field1, field2,...] of the fields at the given
        coordinates. Returns a list of field values in the same order as
        the input *fields*.
        point = self.point(coords)
        ret = []
        field_list = ensure_list(fields)
        for field in field_list:
        if len(field_list) == 1:
            return ret[0]
            return ret

    def find_field_values_at_points(self, fields, coords):
        Returns the values [field1, field2,...] of the fields at the given
        [(x1, y1, z2), (x2, y2, z2),...] points.  Returns a list of field
        values in the same order as the input *fields*.

        # If an optimized version exists on the Index object we'll use that
            return self.index._find_field_values_at_points(fields, coords)
        except AttributeError:

        fields = ensure_list(fields)
        out = []

        # This may be slow because it creates a data object for each point
        for field_index, field in enumerate(fields):
            funit = self._get_field_info[field].units
            out.append(self.arr(np.empty((len(coords),)), funit))
            for coord_index, coord in enumerate(coords):
                out[field_index][coord_index] = self.point(coord)[fields]
        if len(fields) == 1:
            return out[0]
            return out

    # Now all the object related stuff
    def all_data(self, find_max=False, **kwargs):
        all_data is a wrapper to the Region object for creating a region
        which covers the entire simulation domain.
        if find_max: c = self.find_max("density")[1]
        else: c = (self.domain_right_edge + self.domain_left_edge)/2.0
        return self.region(c,
            self.domain_left_edge, self.domain_right_edge, **kwargs)

    def box(self, left_edge, right_edge, **kwargs):
        box is a wrapper to the Region object for creating a region
        without having to specify a *center* value.  It assumes the center
        is the midpoint between the left_edge and right_edge.
        # we handle units in the region data object
        # but need to check if left_edge or right_edge is a
        # list or other non-array iterable before calculating
        # the center
        if not isinstance(left_edge, np.ndarray):
            left_edge = np.array(left_edge, dtype='float64')
        if not isinstance(right_edge, np.ndarray):
            right_edge = np.array(right_edge, dtype='float64')
        c = (left_edge + right_edge)/2.0
        return self.region(c, left_edge, right_edge, **kwargs)

    def _setup_particle_type(self, ptype):
        orig = set(self.field_info.items())
        return [n for n, v in set(self.field_info.items()).difference(orig)]

    def particle_fields_by_type(self):
        fields = defaultdict(list)
        for field in self.field_list:
            if field[0] in self.particle_types_raw:
        return fields

    def particles_exist(self):
        for pt, f in itertools.product(self.particle_types_raw, self.field_list):
            if pt == f[0]:
                return True
        return False

    def particle_type_counts(self):
        if self.particles_exist is False:
            return {}

        # frontends or index implementation can populate this dict while
        # creating the index if they know particle counts at that time
        if self._particle_type_counts is not None:
            return self._particle_type_counts

        self._particle_type_counts = self.index._get_particle_type_counts()
        return self._particle_type_counts

    def ires_factor(self):
        o2 = np.log2(self.refine_by)
        if o2 != int(o2):
            raise RuntimeError
        return int(o2)

    def relative_refinement(self, l0, l1):
        return self.refine_by**(l1-l0)

    def _assign_unit_system(self, unit_system):
        current_mks_unit = None
        magnetic_unit = getattr(self, 'magnetic_unit', None)
        if magnetic_unit is not None:
            # if the magnetic unit is in T, we need to create the code unit
            # system as an MKS-like system
            if current_mks in self.magnetic_unit.units.dimensions.free_symbols:
                if unit_system == "code":
                    current_mks_unit = 'A'
                elif unit_system == 'mks':
                    self.magnetic_unit = \
                        self.magnetic_unit.to_equivalent('gauss', 'CGS')
            self.unit_registry.modify("code_magnetic", self.magnetic_unit)
        if unit_system == "code":
            unit_system = self.unit_registry.unit_system_id
            unit_system = str(unit_system).lower()
        self.unit_system = unit_system_registry[unit_system]

    def _create_unit_registry(self):
        self.unit_registry = UnitRegistry()
        import yt.units.dimensions as dimensions
        self.unit_registry.add("code_length", 1.0, dimensions.length)
        self.unit_registry.add("code_mass", 1.0, dimensions.mass)
        self.unit_registry.add("code_density", 1.0, dimensions.density)
        self.unit_registry.add("code_specific_energy", 1.0,
                      / dimensions.mass)
        self.unit_registry.add("code_time", 1.0, dimensions.time)
        self.unit_registry.add("code_magnetic", 1.0, dimensions.magnetic_field)
        self.unit_registry.add("code_temperature", 1.0, dimensions.temperature)
        self.unit_registry.add("code_pressure", 1.0, dimensions.pressure)
        self.unit_registry.add("code_velocity", 1.0, dimensions.velocity)
        self.unit_registry.add("code_metallicity", 1.0,
        self.unit_registry.add("a", 1.0, dimensions.dimensionless)

    def set_units(self):
        Creates the unit registry for this dataset.

        from yt.units.dimensions import length
        if getattr(self, "cosmological_simulation", False):
            # this dataset is cosmological, so add cosmological units.
            self.unit_registry.modify("h", self.hubble_constant)
            # Comoving lengths
            for my_unit in ["m", "pc", "AU", "au"]:
                new_unit = "%scm" % my_unit
                self.unit_registry.add(new_unit, self.unit_registry.lut[my_unit][0] /
                                       (1 + self.current_redshift),
                                       length, "\\rm{%s}/(1+z)" % my_unit)
            self.unit_registry.modify('a', 1/(1+self.current_redshift))


        if getattr(self, "cosmological_simulation", False):
            # this dataset is cosmological, add a cosmology object

            # Set dynamical dark energy parameters
            use_dark_factor = getattr(self, 'use_dark_factor', False)
            w_0 = getattr(self, 'w_0', -1.0)
            w_a = getattr(self, 'w_a', 0.0)

            self.cosmology = \
                              use_dark_factor = use_dark_factor,
                              w_0 = w_0, w_a = w_a)
            self.critical_density = \
            self.scale_factor = 1.0 / (1.0 + self.current_redshift)

    def get_unit_from_registry(self, unit_str):
        Creates a unit object matching the string expression, using this
        dataset's unit registry.

        unit_str : str
            string that we can parse for a sympy Expr.

        new_unit = Unit(unit_str, registry=self.unit_registry)
        return new_unit

    def set_code_units(self):
        # here we override units, if overrides have been provided.

        # set attributes like ds.length_unit

        self.unit_registry.modify("code_length", self.length_unit)
        self.unit_registry.modify("code_mass", self.mass_unit)
        self.unit_registry.modify("code_time", self.time_unit)
        vel_unit = getattr(
            self, "velocity_unit", self.length_unit / self.time_unit)
        pressure_unit = getattr(
            self, "pressure_unit",
            self.mass_unit / (self.length_unit * (self.time_unit)**2))
        temperature_unit = getattr(self, "temperature_unit", 1.0)
        density_unit = getattr(self, "density_unit", self.mass_unit / self.length_unit**3)
        specific_energy_unit = getattr(self, "specific_energy_unit", vel_unit**2)
        self.unit_registry.modify("code_velocity", vel_unit)
        self.unit_registry.modify("code_temperature", temperature_unit)
        self.unit_registry.modify("code_pressure", pressure_unit)
        self.unit_registry.modify("code_density", density_unit)
        self.unit_registry.modify("code_specific_energy", specific_energy_unit)
        # domain_width does not yet exist
        if (self.domain_left_edge is not None and
            self.domain_right_edge is not None):
            DW = self.arr(self.domain_right_edge - self.domain_left_edge, "code_length")
            self.unit_registry.add("unitary", float(DW.max() * DW.units.base_value),

    def _override_code_units(self):
        if len(self.units_override) == 0:
            "Overriding code units: Use this option only if you know that the "
            "dataset doesn't define the units correctly or at all.")
        for unit, cgs in [("length", "cm"), ("time", "s"), ("mass", "g"),
                          ("velocity","cm/s"), ("magnetic","gauss"),
            val = self.units_override.get("%s_unit" % unit, None)
            if val is not None:
                if isinstance(val, YTQuantity):
                    val = (val.v, str(val.units))
                elif not isinstance(val, tuple):
                    val = (val, cgs)
      "Overriding %s_unit: %g %s.", unit, val[0], val[1])
                setattr(self, "%s_unit" % unit, self.quan(val[0], val[1]))

    _arr = None
    def arr(self):
        """Converts an array into a :class:`yt.units.yt_array.YTArray`

        The returned YTArray will be dimensionless by default, but can be
        cast to arbitrary units using the ``input_units`` keyword argument.


        input_array : Iterable
            A tuple, list, or array to attach units to
        input_units : String unit specification, unit symbol or astropy object
            The units of the array. Powers must be specified using python syntax
            (cm**3, not cm^3).
        dtype : string or NumPy dtype object
            The dtype of the returned array data


        >>> import yt
        >>> import numpy as np
        >>> ds = yt.load('IsolatedGalaxy/galaxy0030/galaxy0030')
        >>> a = ds.arr([1, 2, 3], 'cm')
        >>> b = ds.arr([4, 5, 6], 'm')
        >>> a + b
        YTArray([ 401.,  502.,  603.]) cm
        >>> b + a
        YTArray([ 4.01,  5.02,  6.03]) m

        Arrays returned by this function know about the dataset's unit system

        >>> a = ds.arr(np.ones(5), 'code_length')
        >>> a.in_units('Mpccm/h')
        YTArray([ 1.00010449,  1.00010449,  1.00010449,  1.00010449,
                 1.00010449]) Mpc


        if self._arr is not None:
            return self._arr
        self._arr = functools.partial(YTArray, registry = self.unit_registry)
        return self._arr

    _quan = None
    def quan(self):
        """Converts an scalar into a :class:`yt.units.yt_array.YTQuantity`

        The returned YTQuantity will be dimensionless by default, but can be
        cast to arbitrary units using the ``input_units`` keyword argument.


        input_scalar : an integer or floating point scalar
            The scalar to attach units to
        input_units : String unit specification, unit symbol or astropy object
            The units of the quantity. Powers must be specified using python
            syntax (cm**3, not cm^3).
        dtype : string or NumPy dtype object
            The dtype of the array data.


        >>> import yt
        >>> ds = yt.load('IsolatedGalaxy/galaxy0030/galaxy0030')

        >>> a = ds.quan(1, 'cm')
        >>> b = ds.quan(2, 'm')
        >>> a + b
        201.0 cm
        >>> b + a
        2.01 m

        Quantities created this way automatically know about the unit system
        of the dataset.

        >>> a = ds.quan(5, 'code_length')
        >>> a.in_cgs()
        1.543e+25 cm


        if self._quan is not None:
            return self._quan
        self._quan = functools.partial(YTQuantity, registry=self.unit_registry)
        return self._quan

    def add_field(self, name, function=None, sampling_type=None, **kwargs):
        Dataset-specific call to add_field

        Add a new field, along with supplemental metadata, to the list of
        available fields.  This respects a number of arguments, all of which
        are passed on to the constructor for


        name : str
           is the name of the field.
        function : callable
           A function handle that defines the field.  Should accept
           arguments (field, data)
        units : str
           A plain text string encoding the unit.  Powers must be in
           python syntax (** instead of ^).
        take_log : bool
           Describes whether the field should be logged
        validators : list
           A list of :class:`FieldValidator` objects
        particle_type : bool
           Is this a particle (1D) field?
        vector_field : bool
           Describes the dimensionality of the field.  Currently unused.
        display_name : str
           A name used in the plots
        force_override : bool
           Whether to override an existing derived field. Does not work with
           on-disk fields.

        override = kwargs.get("force_override", False)
        if override and name in self.index.field_list:
            raise RuntimeError("force_override is only meant to be used with "
                               "derived fields, not on-disk fields.")
        # Handle the case where the field has already been added.
        if not override and name in self.field_info:
            mylog.warning("Field %s already exists. To override use " +
                          "force_override=True.", name)
        if kwargs.setdefault('particle_type', False):
            if sampling_type is not None and sampling_type != "particle":
                raise RuntimeError("Clashing definition of 'sampling_type' and "
                               "'particle_type'. Note that 'particle_type' is "
                               "deprecated. Please just use 'sampling_type'.")
                sampling_type = "particle"
        if sampling_type is None:
            warnings.warn("Because 'sampling_type' not specified, yt will "
                          "assume a cell 'sampling_type'", stacklevel=2)
            sampling_type = "cell"
        self.field_info.add_field(name, sampling_type, function=function, **kwargs)
        deps, _ = self.field_info.check_derived_fields([name])

    def add_deposited_particle_field(self, deposit_field, method, kernel_name='cubic',
        """Add a new deposited particle field

        Creates a new deposited field based on the particle *deposit_field*.


        deposit_field : tuple
           The field name tuple of the particle field the deposited field will
           be created from.  This must be a field name tuple so yt can
           appropriately infer the correct particle type.
        method : string
           This is the "method name" which will be looked up in the
           `particle_deposit` namespace as `methodname_deposit`.  Current
           methods include `simple_smooth`, `sum`, `std`, `cic`, `weighted_mean`,
           `mesh_id`, and `nearest`.
        kernel_name : string, default 'cubic'
           This is the name of the smoothing kernel to use. It is only used for
           the `simple_smooth` method and is otherwise ignored. Current
           supported kernel names include `cubic`, `quartic`, `quintic`,
           `wendland2`, `wendland4`, and `wendland6`.
        weight_field : string, default 'particle_mass'
           Weighting field name for deposition method `weighted_mean`.


        The field name tuple for the newly created field.
        if isinstance(deposit_field, tuple):
            ptype, deposit_field = deposit_field[0], deposit_field[1]
            raise RuntimeError

        units = self.field_info[ptype, deposit_field].units
        take_log = self.field_info[ptype, deposit_field].take_log
        name_map = {"sum": "sum", "std":"std", "cic": "cic", "weighted_mean": "avg",
                    "nearest": "nn", "simple_smooth": "ss", "count": "count"}
        field_name = "%s_" + name_map[method] + "_%s"
        field_name = field_name % (ptype, deposit_field.replace('particle_', ''))

        if method == "count":
            field_name = "%s_count" % ptype
            if ("deposit", field_name) in self.field_info:
                mylog.warning("The deposited field %s already exists" % field_name)
                return ("deposit", field_name)
                units = "dimensionless"
                take_log = False

        def _deposit_field(field, data):
            Create a grid field for particle quantities using given method.
            pos = data[ptype, "particle_position"]
            fields = [data[ptype, deposit_field]]
            if method == 'weighted_mean':
                fields.append(data[ptype, weight_field])
            fields = [np.ascontiguousarray(f) for f in fields]
            d = data.deposit(pos, fields, method=method,
            d = data.ds.arr(d, input_units=units)
            if method == 'weighted_mean':
                d[np.isnan(d)] = 0.0
            return d

            ("deposit", field_name),
        return ("deposit", field_name)

    def add_smoothed_particle_field(self, smooth_field,
                                    method="volume_weighted", nneighbors=64,
        """Add a new smoothed particle field

        Creates a new smoothed field based on the particle *smooth_field*.


        smooth_field : tuple
           The field name tuple of the particle field the smoothed field will
           be created from.  This must be a field name tuple so yt can
           appropriately infer the correct particle type.
        method : string, default 'volume_weighted'
           The particle smoothing method to use. Can only be 'volume_weighted'
           for now.
        nneighbors : int, default 64
            The number of neighbors to examine during the process.
        kernel_name : string, default `cubic`
            This is the name of the smoothing kernel to use. Current supported
            kernel names include `cubic`, `quartic`, `quintic`, `wendland2`,
            `wendland4`, and `wendland6`.


        The field name tuple for the newly created field.
        # The magical step

        # Parse arguments
        if isinstance(smooth_field, tuple):
            ptype, smooth_field = smooth_field[0], smooth_field[1]
            raise RuntimeError("smooth_field must be a tuple, received %s" %
        if method != "volume_weighted":
            raise NotImplementedError("method must be 'volume_weighted'")

        # Prepare field names and registry to be used later
        coord_name = "particle_position"
        mass_name = "particle_mass"
        smoothing_length_name = "smoothing_length"
        if (ptype, smoothing_length_name) not in self.derived_field_list:
            raise ValueError("%s not in derived_field_list" %
                             ((ptype, smoothing_length_name),))
        density_name = "density"
        registry = self.field_info

        # Do the actual work
        return add_volume_weighted_smoothed_field(ptype, coord_name, mass_name,
                   smoothing_length_name, density_name, smooth_field, registry,
                   nneighbors=nneighbors, kernel_name=kernel_name)[0]

    def add_gradient_fields(self, input_field):
        """Add gradient fields.

        Creates four new grid-based fields that represent the components of
        the gradient of an existing field, plus an extra field for the magnitude
        of the gradient. Currently only supported in Cartesian geometries. The
        gradient is computed using second-order centered differences.

        input_field : tuple
           The field name tuple of the particle field the deposited field will
           be created from.  This must be a field name tuple so yt can
           appropriately infer the correct field type.

        A list of field name tuples for the newly created fields.

        >>> grad_fields = ds.add_gradient_fields(("gas","temperature"))
        >>> print(grad_fields)
        [('gas', 'temperature_gradient_x'),
         ('gas', 'temperature_gradient_y'),
         ('gas', 'temperature_gradient_z'),
         ('gas', 'temperature_gradient_magnitude')]
        if isinstance(input_field, tuple):
            ftype, input_field = input_field[0], input_field[1]
            raise RuntimeError
        units = self.field_info[ftype, input_field].units
        setup_gradient_fields(self.field_info, (ftype, input_field), units)
        # Now we make a list of the fields that were just made, to check them
        # and to return them
        grad_fields = [(ftype,input_field+"_gradient_%s" % suffix)
                       for suffix in "xyz"]
        deps, _ = self.field_info.check_derived_fields(grad_fields)
        return grad_fields

    _max_level = None
    def max_level(self):
        if self._max_level is None:
            self._max_level = self.index.max_level

        return self._max_level

    def max_level(self, value):
        self._max_level = value

    def define_unit(self, symbol, value, tex_repr=None, offset=None, prefixable=False):
        Define a new unit and add it to the dataset's unit registry.

        symbol : string
            The symbol for the new unit.
        value : tuple or ~yt.units.yt_array.YTQuantity
            The definition of the new unit in terms of some other units. For example,
            one would define a new "mph" unit with (1.0, "mile/hr") 
        tex_repr : string, optional
            The LaTeX representation of the new unit. If one is not supplied, it will
            be generated automatically based on the symbol string.
        offset : float, optional
            The default offset for the unit. If not set, an offset of 0 is assumed.
        prefixable : bool, optional
            Whether or not the new unit can use SI prefixes. Default: False

        >>> ds.define_unit("mph", (1.0, "mile/hr"))
        >>> two_weeks = YTQuantity(14.0, "days")
        >>> ds.define_unit("fortnight", two_weeks)
        _define_unit(self.unit_registry, symbol, value, tex_repr=tex_repr, 
                     offset=offset, prefixable=prefixable)

def _reconstruct_ds(*args, **kwargs):
    datasets = ParameterFileStore()
    ds = datasets.get_ds_hash(*args)
    return ds

class ParticleFile(object):
    def __init__(self, ds, io, filename, file_id):
        self.ds = ds = weakref.proxy(io)
        self.filename = filename
        self.file_id = file_id
        self.total_particles =

    def select(self, selector):

    def count(self, selector):

    def _calculate_offsets(self, fields):

    def __lt__(self, other):
        return self.filename < other.filename

class ParticleDataset(Dataset):
    _unit_base = None
    filter_bbox = False

    def __init__(self, filename, dataset_type=None, file_style=None,
                 units_override=None, unit_system="cgs",
                 n_ref=64, over_refine_factor=1):
        self.n_ref = n_ref
        self.over_refine_factor = over_refine_factor
        super(ParticleDataset, self).__init__(
            filename, dataset_type=dataset_type, file_style=file_style,
            units_override=units_override, unit_system=unit_system)