Source code for sympy.core.symbol

from sympy.core.assumptions import StdFactKB
from basic import Basic
from core import C
from sympify import sympify
from singleton import S
from expr import Expr, AtomicExpr
from cache import cacheit
from function import FunctionClass
from sympy.core.logic import fuzzy_bool
from sympy.logic.boolalg import Boolean
from sympy.utilities.exceptions import SymPyDeprecationWarning

import re

[docs]class Symbol(AtomicExpr, Boolean): """ Assumptions: commutative = True You can override the default assumptions in the constructor: >>> from sympy import symbols >>> A,B = symbols('A,B', commutative = False) >>> bool(A*B != B*A) True >>> bool(A*B*2 == 2*A*B) == True # multiplication by scalars is commutative True """ is_comparable = False __slots__ = ['name'] is_Symbol = True @property def _diff_wrt(self): """Allow derivatives wrt Symbols. Examples ======== >>> from sympy import Symbol >>> x = Symbol('x') >>> x._diff_wrt True """ return True def __new__(cls, name, **assumptions): """Symbols are identified by name and assumptions:: >>> from sympy import Symbol >>> Symbol("x") == Symbol("x") True >>> Symbol("x", real=True) == Symbol("x", real=False) False """ if 'dummy' in assumptions: SymPyDeprecationWarning( feature="Symbol('x', dummy=True)", useinstead="Dummy() or symbols(..., cls=Dummy)", issue=3378, deprecated_since_version="0.7.0", ).warn() if assumptions.pop('dummy'): return Dummy(name, **assumptions) if assumptions.get('zero', False): return S.Zero is_commutative = fuzzy_bool(assumptions.get('commutative', True)) if is_commutative is None: raise ValueError( '''Symbol commutativity must be True or False.''') assumptions['commutative'] = is_commutative return Symbol.__xnew_cached_(cls, name, **assumptions) def __new_stage2__(cls, name, **assumptions): assert isinstance(name, str),repr(type(name)) obj = Expr.__new__(cls) obj.name = name obj._assumptions = StdFactKB(assumptions) return obj __xnew__ = staticmethod(__new_stage2__) # never cached (e.g. dummy) __xnew_cached_ = staticmethod(cacheit(__new_stage2__)) # symbols are always cached def __getnewargs__(self): return (self.name,) def __getstate__(self): return {'_assumptions': self._assumptions} def _hashable_content(self): return (self.name,) + tuple(sorted(self.assumptions0.iteritems())) @property def assumptions0(self): return dict((key, value) for key, value in self._assumptions.iteritems() if value is not None) @cacheit def sort_key(self, order=None): return self.class_key(), (1, (str(self),)), S.One.sort_key(), S.One def as_dummy(self): return Dummy(self.name, **self.assumptions0) def __call__(self, *args): from function import Function return Function(self.name)(*args) def as_real_imag(self, deep=True, **hints): if hints.get('ignore') == self: return None else: return (C.re(self), C.im(self)) def _sage_(self): import sage.all as sage return sage.var(self.name) def is_constant(self, *wrt, **flags): if not wrt: return False return not self in wrt @property def is_number(self): return False @property def free_symbols(self): return set([self])
[docs]class Dummy(Symbol): """Dummy symbols are each unique, identified by an internal count index: >>> from sympy import Dummy >>> bool(Dummy("x") == Dummy("x")) == True False If a name is not supplied then a string value of the count index will be used. This is useful when a temporary variable is needed and the name of the variable used in the expression is not important. >>> Dummy._count = 0 # /!\ this should generally not be changed; it is being >>> Dummy() # used here to make sure that the doctest passes. _0 """ _count = 0 __slots__ = ['dummy_index'] is_Dummy = True def __new__(cls, name=None, **assumptions): if name is None: name = str(Dummy._count) is_commutative = fuzzy_bool(assumptions.get('commutative', True)) if is_commutative is None: raise ValueError( '''Dummy's commutativity must be True or False.''') assumptions['commutative'] = is_commutative obj = Symbol.__xnew__(cls, name, **assumptions) Dummy._count += 1 obj.dummy_index = Dummy._count return obj def __getstate__(self): return {'_assumptions': self._assumptions, 'dummy_index': self.dummy_index} def _hashable_content(self): return Symbol._hashable_content(self) + (self.dummy_index,)
[docs]class Wild(Symbol): """ Wild() matches any expression but another Wild(). """ __slots__ = ['exclude', 'properties'] is_Wild = True def __new__(cls, name, exclude=(), properties=(), **assumptions): exclude = tuple([sympify(x) for x in exclude]) properties = tuple(properties) is_commutative = fuzzy_bool(assumptions.get('commutative', True)) if is_commutative is None: raise ValueError( '''Wild's commutativity must be True or False.''') assumptions['commutative'] = is_commutative return Wild.__xnew__(cls, name, exclude, properties, **assumptions) def __getnewargs__(self): return (self.name, self.exclude, self.properties) @staticmethod @cacheit def __xnew__(cls, name, exclude, properties, **assumptions): obj = Symbol.__xnew__(cls, name, **assumptions) obj.exclude = exclude obj.properties = properties return obj def _hashable_content(self): return super(Wild, self)._hashable_content() + (self.exclude, self.properties) # TODO add check against another Wild def matches(self, expr, repl_dict={}): if any(expr.has(x) for x in self.exclude): return None if any(not f(expr) for f in self.properties): return None repl_dict = repl_dict.copy() repl_dict[self] = expr return repl_dict def __call__(self, *args, **kwargs): raise TypeError("'%s' object is not callable" % type(self).__name__)
_re_var_range = re.compile(r"^(.*?)(\d*):(\d+)$") _re_var_scope = re.compile(r"^(.):(.)$") _re_var_split = re.compile(r"\s*,\s*|\s+")
[docs]def symbols(names, **args): """ Transform strings into instances of :class:`Symbol` class. :func:`symbols` function returns a sequence of symbols with names taken from ``names`` argument, which can be a comma or whitespace delimited string, or a sequence of strings:: >>> from sympy import symbols, Function >>> x, y, z = symbols('x,y,z') >>> a, b, c = symbols('a b c') The type of output is dependent on the properties of input arguments:: >>> symbols('x') x >>> symbols('x,') (x,) >>> symbols('x,y') (x, y) >>> symbols(('a', 'b', 'c')) (a, b, c) >>> symbols(['a', 'b', 'c']) [a, b, c] >>> symbols(set(['a', 'b', 'c'])) set([a, b, c]) If an iterable container is needed for a single symbol, set the ``seq`` argument to ``True`` or terminate the symbol name with a comma:: >>> symbols('x', seq=True) (x,) To reduce typing, range syntax is supported to create indexed symbols:: >>> symbols('x:10') (x0, x1, x2, x3, x4, x5, x6, x7, x8, x9) >>> symbols('x5:10') (x5, x6, x7, x8, x9) >>> symbols('x5:10,y:5') (x5, x6, x7, x8, x9, y0, y1, y2, y3, y4) >>> symbols(('x5:10', 'y:5')) ((x5, x6, x7, x8, x9), (y0, y1, y2, y3, y4)) To reduce typing even more, lexicographic range syntax is supported:: >>> symbols('x:z') (x, y, z) >>> symbols('a:d,x:z') (a, b, c, d, x, y, z) >>> symbols(('a:d', 'x:z')) ((a, b, c, d), (x, y, z)) All newly created symbols have assumptions set accordingly to ``args``:: >>> a = symbols('a', integer=True) >>> a.is_integer True >>> x, y, z = symbols('x,y,z', real=True) >>> x.is_real and y.is_real and z.is_real True Despite its name, :func:`symbols` can create symbol--like objects of other type, for example instances of Function or Wild classes. To achieve this, set ``cls`` keyword argument to the desired type:: >>> symbols('f,g,h', cls=Function) (f, g, h) >>> type(_[0]) <class 'sympy.core.function.UndefinedFunction'> """ result = [] if 'each_char' in args: if args['each_char']: value = "Tip: ' '.join(s) will transform a string s = 'xyz' to 'x y z'." else: value = "" SymPyDeprecationWarning( feature="each_char in the options to symbols() and var()", useinstead="spaces or commas between symbol names", issue=1919, deprecated_since_version="0.7.0", value=value ).warn() if isinstance(names, basestring): names = names.strip() as_seq= names.endswith(',') if as_seq: names = names[:-1].rstrip() if not names: raise ValueError('no symbols given') names = _re_var_split.split(names) if args.pop('each_char', False) and not as_seq and len(names) == 1: return symbols(tuple(names[0]), **args) cls = args.pop('cls', Symbol) seq = args.pop('seq', as_seq) for name in names: if not name: raise ValueError('missing symbol') if ':' not in name: symbol = cls(name, **args) result.append(symbol) continue match = _re_var_range.match(name) if match is not None: name, start, end = match.groups() if not start: start = 0 else: start = int(start) for i in xrange(start, int(end)): symbol = cls("%s%i" % (name, i), **args) result.append(symbol) seq = True continue match = _re_var_scope.match(name) if match is not None: start, end = match.groups() for name in xrange(ord(start), ord(end)+1): symbol = cls(chr(name), **args) result.append(symbol) seq = True continue raise ValueError("'%s' is not a valid symbol range specification" % name) if not seq and len(result) <= 1: if not result: raise ValueError('missing symbol') # should never happen return result[0] return tuple(result) else: for name in names: result.append(symbols(name, **args)) return type(names)(result)
[docs]def var(names, **args): """ Create symbols and inject them into the global namespace. This calls :func:`symbols` with the same arguments and puts the results into the *global* namespace. It's recommended not to use :func:`var` in library code, where :func:`symbols` has to be used:: >>> from sympy import var >>> var('x') x >>> x x >>> var('a,ab,abc') (a, ab, abc) >>> abc abc >>> var('x,y', real=True) (x, y) >>> x.is_real and y.is_real True See :func:`symbol` documentation for more details on what kinds of arguments can be passed to :func:`var`. """ def traverse(symbols, frame): """Recursively inject symbols to the global namespace. """ for symbol in symbols: if isinstance(symbol, Basic): frame.f_globals[symbol.name] = symbol elif isinstance(symbol, FunctionClass): frame.f_globals[symbol.__name__] = symbol else: traverse(symbol, frame) from inspect import currentframe frame = currentframe().f_back try: syms = symbols(names, **args) if syms is not None: if isinstance(syms, Basic): frame.f_globals[syms.name] = syms elif isinstance(syms, FunctionClass): frame.f_globals[syms.__name__] = syms else: traverse(syms, frame) finally: del frame # break cyclic dependencies as stated in inspect docs return syms