Source code for yt.units.unit_object

A class that represents a unit symbol.


# 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.

from yt.extern.six import text_type
from sympy import \
    Expr, Mul, Add, Number, \
    Pow, Symbol, Integer, \
    Float, Basic, Rational, sqrt
from sympy.core.numbers import One
from sympy import sympify, latex
from sympy.parsing.sympy_parser import \
    parse_expr, auto_number, rationalize
from keyword import iskeyword
from yt.units.dimensions import \
    base_dimensions, temperature, \
    dimensionless, current_mks, \
from yt.units.equivalencies import \
from yt.units.unit_lookup_table import \
    unit_prefixes, prefixable_units, latex_prefixes, \
from yt.units.unit_registry import \
    UnitRegistry, \
from yt.utilities.exceptions import YTUnitsNotReducible

import copy
import token

[docs]class InvalidUnitOperation(Exception): pass
default_unit_registry = UnitRegistry() sympy_one = sympify(1) global_dict = { 'Symbol': Symbol, 'Integer': Integer, 'Float': Float, 'Rational': Rational, 'sqrt': sqrt } unit_system_registry = {}
[docs]def auto_positive_symbol(tokens, local_dict, global_dict): """ Inserts calls to ``Symbol`` for undefined variables. Passes in positive=True as a keyword argument. Adapted from sympy.sympy.parsing.sympy_parser.auto_symbol """ result = [] prevTok = (None, None) tokens.append((None, None)) # so zip traverses all tokens for tok, nextTok in zip(tokens, tokens[1:]): tokNum, tokVal = tok nextTokNum, nextTokVal = nextTok if tokNum == token.NAME: name = tokVal if (name in ['True', 'False', 'None'] or iskeyword(name) or name in local_dict # Don't convert attribute access or (prevTok[0] == token.OP and prevTok[1] == '.') # Don't convert keyword arguments or (prevTok[0] == token.OP and prevTok[1] in ('(', ',') and nextTokNum == token.OP and nextTokVal == '=')): result.append((token.NAME, name)) continue elif name in global_dict: obj = global_dict[name] if isinstance(obj, (Basic, type)) or callable(obj): result.append((token.NAME, name)) continue result.extend([ (token.NAME, 'Symbol'), (token.OP, '('), (token.NAME, repr(str(name))), (token.OP, ','), (token.NAME, 'positive'), (token.OP, '='), (token.NAME, 'True'), (token.OP, ')'), ]) else: result.append((tokNum, tokVal)) prevTok = (tokNum, tokVal) return result
[docs]def get_latex_representation(expr, registry): symbol_table = {} for ex in expr.free_symbols: try: symbol_table[ex] = registry.lut[str(ex)][3] except: symbol_table[ex] = r"\rm{" + str(ex).replace('_', '\ ') + "}" # invert the symbol table dict to look for keys with identical values invert_symbols = {} for key, value in symbol_table.items(): if value not in invert_symbols: invert_symbols[value] = [key] else: invert_symbols[value].append(key) # if there are any units with identical latex representations, substitute # units to avoid uncanceled terms in the final latex expresion. for val in invert_symbols: symbols = invert_symbols[val] for i in range(1, len(symbols)): expr = expr.subs(symbols[i], symbols[0]) prefix = None if isinstance(expr, Mul): coeffs = expr.as_coeff_Mul() if coeffs[0] == 1 or not isinstance(coeffs[0], Float): pass else: expr = coeffs[1] prefix = Float(coeffs[0], 2) latex_repr = latex(expr, symbol_names=symbol_table, mul_symbol="dot", fold_frac_powers=True, fold_short_frac=True) if prefix is not None: latex_repr = latex(prefix, mul_symbol="times") + '\\ ' + latex_repr if latex_repr == '1': return '' else: return latex_repr
unit_text_transform = (auto_positive_symbol, rationalize, auto_number)
[docs]class Unit(Expr): """ A symbolic unit, using sympy functionality. We only add "dimensions" so that sympy understands relations between different units. """ # Set some assumptions for sympy. is_positive = True # make sqrt(m**2) --> m is_commutative = True is_number = False # Extra attributes __slots__ = ["expr", "is_atomic", "base_value", "base_offset", "dimensions", "registry", "_latex_repr"] def __new__(cls, unit_expr=sympy_one, base_value=None, base_offset=0.0, dimensions=None, registry=None, latex_repr=None, **assumptions): """ Create a new unit. May be an atomic unit (like a gram) or combinations of atomic units (like g / cm**3). Parameters ---------- unit_expr : Unit object, sympy.core.expr.Expr object, or str The symbolic unit expression. base_value : float The unit's value in yt's base units. base_offset : float The offset necessary to normalize temperature units to a common zero point. dimensions : sympy.core.expr.Expr A sympy expression representing the dimensionality of this unit. It must contain only mass, length, time, temperature and angle symbols. registry : UnitRegistry object The unit registry we use to interpret unit symbols. latex_repr : string A string to render the unit as LaTeX Additional keyword arguments are passed as assumptions to the Sympy Expr initializer """ # Simplest case. If user passes a Unit object, just use the expr. unit_key = None if isinstance(unit_expr, (str, bytes, text_type)): if isinstance(unit_expr, bytes): unit_expr = unit_expr.decode("utf-8") if registry and unit_expr in registry.unit_objs: return registry.unit_objs[unit_expr] else: unit_key = unit_expr if not unit_expr: # Bug catch... # if unit_expr is an empty string, parse_expr fails hard... unit_expr = "1" try: unit_expr = parse_expr(unit_expr, global_dict=global_dict, transformations=unit_text_transform) except SyntaxError as e: msg = ("Unit expression %s raised an error " "during parsing:\n%s" % (unit_expr, repr(e))) raise UnitParseError(msg) elif isinstance(unit_expr, Unit): # grab the unit object's sympy expression. unit_expr = unit_expr.expr elif hasattr(unit_expr, 'units') and hasattr(unit_expr, 'value'): # something that looks like a YTArray, grab the unit and value if unit_expr.shape != (): raise UnitParseError( 'Cannot create a unit from a non-scalar YTArray, received: ' '%s' % (unit_expr, )) value = unit_expr.value if value == 1: unit_expr = unit_expr.units.expr else: unit_expr = unit_expr.value*unit_expr.units.expr # Make sure we have an Expr at this point. if not isinstance(unit_expr, Expr): raise UnitParseError("Unit representation must be a string or " \ "sympy Expr. %s has type %s." \ % (unit_expr, type(unit_expr))) if unit_expr == sympy_one and dimensions is None: dimensions = dimensionless if registry is None: # Caller did not set the registry, so use the default. registry = default_unit_registry # done with argument checking... # see if the unit is atomic. is_atomic = False if isinstance(unit_expr, Symbol): is_atomic = True # # check base_value and dimensions # if base_value is not None: # check that base_value is a float or can be converted to one try: base_value = float(base_value) except ValueError: raise UnitParseError("Could not use base_value as a float. " \ "base_value is '%s' (type %s)." \ % (base_value, type(base_value)) ) # check that dimensions is valid if dimensions is not None: validate_dimensions(dimensions) else: # lookup the unit symbols unit_data = _get_unit_data_from_expr(unit_expr, registry.lut) base_value = unit_data[0] dimensions = unit_data[1] if len(unit_data) > 2: base_offset = unit_data[2] latex_repr = unit_data[3] else: base_offset = 0.0 # Create obj with superclass construct. obj = Expr.__new__(cls, **assumptions) # Attach attributes to obj. obj.expr = unit_expr obj.is_atomic = is_atomic obj.base_value = base_value obj.base_offset = base_offset obj.dimensions = dimensions obj._latex_repr = latex_repr obj.registry = registry if unit_key is not None: registry.unit_objs[unit_key] = obj # Return `obj` so __init__ can handle it. return obj _latex_expr = None @property def latex_repr(self): if self._latex_repr is not None: return self._latex_repr if self.expr.is_Atom: expr = self.expr else: expr = self.expr.copy() self._latex_repr = get_latex_representation(expr, self.registry) return self._latex_repr ### Some sympy conventions def __getnewargs__(self): return (self.expr, self.is_atomic, self.base_value, self.dimensions, self.registry) def __hash__(self): return super(Unit, self).__hash__() def _hashable_content(self): return (self.expr, self.is_atomic, self.base_value, self.dimensions, self.registry) ### end sympy conventions def __repr__(self): if self.expr == sympy_one: return "(dimensionless)" # @todo: don't use dunder method? return self.expr.__repr__() def __str__(self): if self.expr == sympy_one: return "dimensionless" # @todo: don't use dunder method? return self.expr.__str__() # for sympy.printing def _sympystr(self, *args): return str(self.expr) # # Start unit operations # def __mul__(self, u): """ Multiply Unit with u (Unit object). """ if not isinstance(u, Unit): raise InvalidUnitOperation("Tried to multiply a Unit object with " "'%s' (type %s). This behavior is " "undefined." % (u, type(u))) base_offset = 0.0 if self.base_offset or u.base_offset: if u.dimensions in (temperature, angle) and self.is_dimensionless: base_offset = u.base_offset elif self.dimensions in (temperature, angle) and u.is_dimensionless: base_offset = self.base_offset else: raise InvalidUnitOperation("Quantities with units of Fahrenheit " "and Celsius or angles cannot be multiplied.") return Unit(self.expr * u.expr, base_value=(self.base_value * u.base_value), base_offset=base_offset, dimensions=(self.dimensions * u.dimensions), registry=self.registry) def __div__(self, u): """ Divide Unit by u (Unit object). """ if not isinstance(u, Unit): raise InvalidUnitOperation("Tried to divide a Unit object by '%s' " "(type %s). This behavior is " "undefined." % (u, type(u))) base_offset = 0.0 if self.base_offset or u.base_offset: if u.dimensions in (temperature, angle) and self.is_dimensionless: base_offset = u.base_offset elif self.dimensions in (temperature, angle) and u.is_dimensionless: base_offset = self.base_offset else: raise InvalidUnitOperation("Quantities with units of Farhenheit " "and Celsius cannot be multiplied.") return Unit(self.expr / u.expr, base_value=(self.base_value / u.base_value), base_offset=base_offset, dimensions=(self.dimensions / u.dimensions), registry=self.registry) __truediv__ = __div__ def __pow__(self, p): """ Take Unit to power p (float). """ try: p = Rational(str(p)).limit_denominator() except ValueError: raise InvalidUnitOperation("Tried to take a Unit object to the " \ "power '%s' (type %s). Failed to cast " \ "it to a float." % (p, type(p)) ) return Unit(self.expr**p, base_value=(self.base_value**p), dimensions=(self.dimensions**p), registry=self.registry) def __eq__(self, u): """ Test unit equality. """ if not isinstance(u, Unit): return False return \ (self.base_value == u.base_value and self.dimensions == u.dimensions) def __ne__(self, u): """ Test unit inequality. """ if not isinstance(u, Unit): return True if self.base_value != u.base_value: return True # use 'is' comparison dimensions to avoid expensive sympy operation if self.dimensions is u.dimensions: return False return self.dimensions != u.dimensions
[docs] def copy(self): return copy.deepcopy(self)
def __deepcopy__(self, memodict=None): if memodict is None: memodict = {} expr = str(self.expr) base_value = copy.deepcopy(self.base_value) base_offset = copy.deepcopy(self.base_offset) dimensions = copy.deepcopy(self.dimensions) lut = copy.deepcopy(self.registry.lut) registry = UnitRegistry(lut=lut) return Unit(expr, base_value, base_offset, dimensions, registry) # # End unit operations #
[docs] def same_dimensions_as(self, other_unit): """ Test if dimensions are the same. """ # test first for 'is' equality to avoid expensive sympy operation if self.dimensions is other_unit.dimensions: return True return (self.dimensions / other_unit.dimensions) == sympy_one
@property def is_dimensionless(self): return self.dimensions is sympy_one @property def is_code_unit(self): for atom in self.expr.atoms(): if str(atom).startswith("code") or atom.is_Number: pass else: return False return True
[docs] def list_equivalencies(self): """ Lists the possible equivalencies associated with this unit object """ for k, v in equivalence_registry.items(): if self.has_equivalent(k): print(v())
[docs] def has_equivalent(self, equiv): """ Check to see if this unit object as an equivalent unit in *equiv*. """ try: this_equiv = equivalence_registry[equiv]() except KeyError: raise KeyError("No such equivalence \"%s\"." % equiv) old_dims = self.dimensions return old_dims in this_equiv.dims
[docs] def get_base_equivalent(self, unit_system="cgs"): """ Create and return dimensionally-equivalent units in a specified base. """ yt_base_unit_string = _get_system_unit_string(self.dimensions, default_base_units) yt_base_unit = Unit(yt_base_unit_string, base_value=1.0, dimensions=self.dimensions, registry=self.registry) if unit_system == "cgs": if current_mks in self.dimensions.free_symbols: raise YTUnitsNotReducible(self, "cgs") return yt_base_unit else: if hasattr(unit_system, "unit_registry"): unit_system = unit_system.unit_registry.unit_system_id elif unit_system == "code": unit_system = self.registry.unit_system_id unit_system = unit_system_registry[str(unit_system)] units_string = _get_system_unit_string(self.dimensions, unit_system.base_units) u = Unit(units_string, registry=self.registry) base_value = get_conversion_factor(self, yt_base_unit)[0] base_value /= get_conversion_factor(self, u)[0] return Unit(units_string, base_value=base_value, dimensions=self.dimensions, registry=self.registry)
[docs] def get_cgs_equivalent(self): """ Create and return dimensionally-equivalent cgs units. """ return self.get_base_equivalent(unit_system="cgs")
[docs] def get_mks_equivalent(self): """ Create and return dimensionally-equivalent mks units. """ return self.get_base_equivalent(unit_system="mks")
[docs] def get_conversion_factor(self, other_units): return get_conversion_factor(self, other_units)
[docs] def latex_representation(self): return self.latex_repr
# # Unit manipulation functions #
[docs]def get_conversion_factor(old_units, new_units): """ Get the conversion factor between two units of equivalent dimensions. This is the number you multiply data by to convert from values in `old_units` to values in `new_units`. Parameters ---------- old_units: str or Unit object The current units. new_units : str or Unit object The units we want. Returns ------- conversion_factor : float `old_units / new_units` offset : float or None Offset between the old unit and new unit. """ ratio = old_units.base_value / new_units.base_value if old_units.base_offset == 0 and new_units.base_offset == 0: return (ratio, None) else: if old_units.dimensions in (temperature, angle): return ratio, ratio*old_units.base_offset - new_units.base_offset else: raise InvalidUnitOperation( "Fahrenheit and Celsius are not absolute temperature scales " "and cannot be used in compound unit symbols.")
# # Helper functions # def _get_unit_data_from_expr(unit_expr, unit_symbol_lut): """ Grabs the total base_value and dimensions from a valid unit expression. Parameters ---------- unit_expr: Unit object, or sympy Expr object The expression containing unit symbols. unit_symbol_lut: dict Provides the unit data for each valid unit symbol. """ # The simplest case first if isinstance(unit_expr, Unit): return (unit_expr.base_value, unit_expr.dimensions) # Now for the sympy possibilities if isinstance(unit_expr, Symbol): return _lookup_unit_symbol(str(unit_expr), unit_symbol_lut) if isinstance(unit_expr, Number): return (float(unit_expr), sympy_one) if isinstance(unit_expr, Pow): unit_data = _get_unit_data_from_expr(unit_expr.args[0], unit_symbol_lut) power = unit_expr.args[1] if isinstance(power, Symbol): raise UnitParseError("Invalid unit expression '%s'." % unit_expr) conv = float(unit_data[0]**power) unit = unit_data[1]**power return (conv, unit) if isinstance(unit_expr, Mul): base_value = 1.0 dimensions = 1 for expr in unit_expr.args: unit_data = _get_unit_data_from_expr(expr, unit_symbol_lut) base_value *= unit_data[0] dimensions *= unit_data[1] return (float(base_value), dimensions) raise UnitParseError("Cannot parse for unit data from '%s'. Please supply" \ " an expression of only Unit, Symbol, Pow, and Mul" \ "objects." % str(unit_expr)) def _lookup_unit_symbol(symbol_str, unit_symbol_lut): """ Searches for the unit data tuple corresponding to the given symbol. Parameters ---------- symbol_str : str The unit symbol to look up. unit_symbol_lut : dict Dictionary with symbols as keys and unit data tuples as values. """ if symbol_str in unit_symbol_lut: # lookup successful, return the tuple directly return unit_symbol_lut[symbol_str] # could still be a known symbol with a prefix possible_prefix = symbol_str[0] if possible_prefix in unit_prefixes: # the first character could be a prefix, check the rest of the symbol symbol_wo_prefix = symbol_str[1:] unit_is_si_prefixable = (symbol_wo_prefix in unit_symbol_lut and symbol_wo_prefix in prefixable_units) if unit_is_si_prefixable is True: # lookup successful, it's a symbol with a prefix unit_data = unit_symbol_lut[symbol_wo_prefix] prefix_value = unit_prefixes[possible_prefix] if possible_prefix in latex_prefixes: latex_repr = symbol_str.replace( possible_prefix, '{'+latex_prefixes[possible_prefix]+'}') else: # Need to add some special handling for comoving units # this is fine for now, but it wouldn't work for a general # unit that has an arbitrary LaTeX representation if symbol_wo_prefix != 'cm' and symbol_wo_prefix.endswith('cm'): sub_symbol_wo_prefix = symbol_wo_prefix[:-2] sub_symbol_str = symbol_str[:-2] else: sub_symbol_wo_prefix = symbol_wo_prefix sub_symbol_str = symbol_str latex_repr = unit_data[3].replace( '{' + sub_symbol_wo_prefix + '}', '{' + sub_symbol_str + '}') # Leave offset and dimensions the same, but adjust scale factor and # LaTeX representation ret = (unit_data[0] * prefix_value, unit_data[1], unit_data[2], latex_repr) unit_symbol_lut[symbol_str] = ret return ret # no dice if symbol_str.startswith('code_'): raise UnitParseError( "Code units have not been defined. \n" "Try creating the array or quantity using ds.arr or ds.quan instead.") else: raise UnitParseError("Could not find unit symbol '%s' in the provided " \ "symbols." % symbol_str)
[docs]def validate_dimensions(dimensions): if isinstance(dimensions, Mul): for dim in dimensions.args: validate_dimensions(dim) elif isinstance(dimensions, Symbol): if dimensions not in base_dimensions: raise UnitParseError("Dimensionality expression contains an " "unknown symbol '%s'." % dimensions) elif isinstance(dimensions, Pow): if not isinstance(dimensions.args[1], Number): raise UnitParseError("Dimensionality expression '%s' contains a " "unit symbol as a power." % dimensions) elif isinstance(dimensions, (Add, Number)): if not isinstance(dimensions, One): raise UnitParseError("Only dimensions that are instances of Pow, " "Mul, or symbols in the base dimensions are " "allowed. Got dimensions '%s'" % dimensions) elif not isinstance(dimensions, Basic): raise UnitParseError("Bad dimensionality expression '%s'." % dimensions)
def _get_system_unit_string(dimensions, base_units): # The dimensions of a unit object is the product of the base dimensions. # Use sympy to factor the dimensions into base CGS unit symbols. units = [] my_dims = dimensions.expand() if my_dims is dimensionless: return "" if my_dims in base_units: return base_units[my_dims] for factor in my_dims.as_ordered_factors(): dim = list(factor.free_symbols)[0] unit_string = str(base_units[dim]) if factor.is_Pow: power_string = "**(%s)" % factor.as_base_exp()[1] else: power_string = "" units.append("(%s)%s" % (unit_string, power_string)) return " * ".join(units) def _define_unit(registry, symbol, value, tex_repr=None, offset=None, prefixable=False): from yt.units.yt_array import YTQuantity, iterable if symbol in registry: raise RuntimeError("The symbol \"%s\" is already in the unit registry!" % symbol) if not isinstance(value, YTQuantity): if iterable(value) and len(value) == 2: value = YTQuantity(value[0], value[1]) else: raise RuntimeError("\"value\" needs to be a (value, unit) tuple!") base_value = float(value.in_base(unit_system='cgs-ampere')) dimensions = value.units.dimensions registry.add(symbol, base_value, dimensions, tex_repr=tex_repr, offset=offset) if prefixable: prefixable_units.append(symbol)
[docs]def define_unit(symbol, value, tex_repr=None, offset=None, prefixable=False): """ Define a new unit and add it to the default unit registry. Parameters ---------- 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 : boolean, optional Whether or not the new unit can use SI prefixes. Default: False Examples -------- >>> yt.define_unit("mph", (1.0, "mile/hr")) >>> two_weeks = YTQuantity(14.0, "days") >>> yt.define_unit("fortnight", two_weeks) """ _define_unit(default_unit_registry, symbol, value, tex_repr=tex_repr, offset=offset, prefixable=prefixable)