Source code for sympy.core.symbol

from __future__ import print_function, division

from sympy.core.assumptions import StdFactKB
from sympy.core.compatibility import string_types, range, is_sequence
from .basic import Basic
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.iterables import cartes

import string
import re as _re
import random


def _symbol(s, matching_symbol=None, **assumptions):
    """Return s if s is a Symbol, else if s is a string, return either
    the matching_symbol if the names are the same or else a new symbol
    with the same assumptions as the matching symbol (or the
    assumptions as provided).

    Examples
    ========

    >>> from sympy import Symbol, Dummy
    >>> from sympy.core.symbol import _symbol
    >>> _symbol('y')
    y
    >>> _.is_real is None
    True
    >>> _symbol('y', real=True).is_real
    True

    >>> x = Symbol('x')
    >>> _symbol(x, real=True)
    x
    >>> _.is_real is None  # ignore attribute if s is a Symbol
    True

    Below, the variable sym has the name 'foo':

    >>> sym = Symbol('foo', real=True)

    Since 'x' is not the same as sym's name, a new symbol is created:

    >>> _symbol('x', sym).name
    'x'

    It will acquire any assumptions give:

    >>> _symbol('x', sym, real=False).is_real
    False

    Since 'foo' is the same as sym's name, sym is returned

    >>> _symbol('foo', sym)
    foo

    Any assumptions given are ignored:

    >>> _symbol('foo', sym, real=False).is_real
    True

    NB: the symbol here may not be the same as a symbol with the same
    name defined elsewhere as a result of different assumptions.

    See Also
    ========

    sympy.core.symbol.Symbol

    """
    if isinstance(s, string_types):
        if matching_symbol and matching_symbol.name == s:
            return matching_symbol
        return Symbol(s, **assumptions)
    elif isinstance(s, Symbol):
        return s
    else:
        raise ValueError('symbol must be string for symbol name or Symbol')


def _uniquely_named_symbol(xname, exprs=(), compare=str, modify=None, **assumptions):
    """Return a symbol which, when printed, will have a name unique
    from any other already in the expressions given. The name is made
    unique by prepending underscores (default) but this can be
    customized with the keyword 'modify'.

    Parameters
    ==========

        xname : a string or a Symbol (when symbol xname <- str(xname))
        compare : a single arg function that takes a symbol and returns
            a string to be compared with xname (the default is the str
            function which indicates how the name will look when it
            is printed, e.g. this includes underscores that appear on
            Dummy symbols)
        modify : a single arg function that changes its string argument
            in some way (the default is to preppend underscores)

    Examples
    ========

    >>> from sympy.core.symbol import _uniquely_named_symbol as usym, Dummy
    >>> from sympy.abc import x
    >>> usym('x', x)
    _x
    """
    default = None
    if is_sequence(xname):
        xname, default = xname
    x = str(xname)
    if not exprs:
        return _symbol(x, default, **assumptions)
    if not is_sequence(exprs):
        exprs = [exprs]
    syms = set().union(*[e.free_symbols for e in exprs])
    if modify is None:
        modify = lambda s: '_' + s
    while any(x == compare(s) for s in syms):
        x = modify(x)
    return _symbol(x, default, **assumptions)


[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 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 @staticmethod def _sanitize(assumptions, obj=None): """Remove None, covert values to bool, check commutativity *in place*. """ # be strict about commutativity: cannot be None is_commutative = fuzzy_bool(assumptions.get('commutative', True)) if is_commutative is None: whose = '%s ' % obj.__name__ if obj else '' raise ValueError( '%scommutativity must be True or False.' % whose) # sanitize other assumptions so 1 -> True and 0 -> False for key in list(assumptions.keys()): from collections import defaultdict from sympy.utilities.exceptions import SymPyDeprecationWarning keymap = defaultdict(lambda: None) keymap.update({'bounded': 'finite', 'unbounded': 'infinite', 'infinitesimal': 'zero'}) if keymap[key]: SymPyDeprecationWarning( feature="%s assumption" % key, useinstead="%s" % keymap[key], issue=8071, deprecated_since_version="0.7.6").warn() assumptions[keymap[key]] = assumptions[key] assumptions.pop(key) key = keymap[key] v = assumptions[key] if v is None: assumptions.pop(key) continue assumptions[key] = bool(v) 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 """ cls._sanitize(assumptions, cls) return Symbol.__xnew_cached_(cls, name, **assumptions) def __new_stage2__(cls, name, **assumptions): if not isinstance(name, string_types): raise TypeError("name should be a string, not %s" % repr(type(name))) obj = Expr.__new__(cls) obj.name = name # TODO: Issue #8873: Forcing the commutative assumption here means # later code such as ``srepr()`` cannot tell whether the user # specified ``commutative=True`` or omitted it. To workaround this, # we keep a copy of the assumptions dict, then create the StdFactKB, # and finally overwrite its ``._generator`` with the dict copy. This # is a bit of a hack because we assume StdFactKB merely copies the # given dict as ``._generator``, but future modification might, e.g., # compute a minimal equivalent assumption set. tmp_asm_copy = assumptions.copy() # be strict about commutativity is_commutative = fuzzy_bool(assumptions.get('commutative', True)) assumptions['commutative'] = is_commutative obj._assumptions = StdFactKB(assumptions) obj._assumptions._generator = tmp_asm_copy # Issue #8873 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): # Note: user-specified assumptions not hashed, just derived ones return (self.name,) + tuple(sorted(self.assumptions0.items())) @property def assumptions0(self): return dict((key, value) for key, value in self._assumptions.items() 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
[docs] def as_dummy(self): """Return a Dummy having the same name and same assumptions as self.""" return Dummy(self.name, **self._assumptions.generator)
def __call__(self, *args): from .function import Function return Function(self.name)(*args) def as_real_imag(self, deep=True, **hints): from sympy import im, re if hints.get('ignore') == self: return None else: return (re(self), 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 free_symbols(self): return {self} binary_symbols = free_symbols # in this case, not always def as_set(self): return S.UniversalSet
[docs]class Dummy(Symbol): """Dummy symbols are each unique, even if they have the same name: >>> from sympy import Dummy >>> Dummy("x") == Dummy("x") False If a name is not supplied then a string value of an internal count 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() #doctest: +SKIP _Dummy_10 """ # In the rare event that a Dummy object needs to be recreated, both the # `name` and `dummy_index` should be passed. This is used by `srepr` for # example: # >>> d1 = Dummy() # >>> d2 = eval(srepr(d1)) # >>> d2 == d1 # True # # If a new session is started between `srepr` and `eval`, there is a very # small chance that `d2` will be equal to a previously-created Dummy. _count = 0 _prng = random.Random() _base_dummy_index = _prng.randint(10**6, 9*10**6) __slots__ = ['dummy_index'] is_Dummy = True def __new__(cls, name=None, dummy_index=None, **assumptions): if dummy_index is not None: assert name is not None, "If you specify a dummy_index, you must also provide a name" if name is None: name = "Dummy_" + str(Dummy._count) if dummy_index is None: dummy_index = Dummy._base_dummy_index + Dummy._count Dummy._count += 1 cls._sanitize(assumptions, cls) obj = Symbol.__xnew__(cls, name, **assumptions) obj.dummy_index = dummy_index return obj def __getstate__(self): return {'_assumptions': self._assumptions, 'dummy_index': self.dummy_index} @cacheit def sort_key(self, order=None): return self.class_key(), ( 2, (str(self), self.dummy_index)), S.One.sort_key(), S.One def _hashable_content(self): return Symbol._hashable_content(self) + (self.dummy_index,)
[docs]class Wild(Symbol): """ A Wild symbol matches anything, or anything without whatever is explicitly excluded. Examples ======== >>> from sympy import Wild, WildFunction, cos, pi >>> from sympy.abc import x, y, z >>> a = Wild('a') >>> x.match(a) {a_: x} >>> pi.match(a) {a_: pi} >>> (3*x**2).match(a*x) {a_: 3*x} >>> cos(x).match(a) {a_: cos(x)} >>> b = Wild('b', exclude=[x]) >>> (3*x**2).match(b*x) >>> b.match(a) {a_: b_} >>> A = WildFunction('A') >>> A.match(a) {a_: A_} Tips ==== When using Wild, be sure to use the exclude keyword to make the pattern more precise. Without the exclude pattern, you may get matches that are technically correct, but not what you wanted. For example, using the above without exclude: >>> from sympy import symbols >>> a, b = symbols('a b', cls=Wild) >>> (2 + 3*y).match(a*x + b*y) {a_: 2/x, b_: 3} This is technically correct, because (2/x)*x + 3*y == 2 + 3*y, but you probably wanted it to not match at all. The issue is that you really didn't want a and b to include x and y, and the exclude parameter lets you specify exactly this. With the exclude parameter, the pattern will not match. >>> a = Wild('a', exclude=[x, y]) >>> b = Wild('b', exclude=[x, y]) >>> (2 + 3*y).match(a*x + b*y) Exclude also helps remove ambiguity from matches. >>> E = 2*x**3*y*z >>> a, b = symbols('a b', cls=Wild) >>> E.match(a*b) {a_: 2*y*z, b_: x**3} >>> a = Wild('a', exclude=[x, y]) >>> E.match(a*b) {a_: z, b_: 2*x**3*y} >>> a = Wild('a', exclude=[x, y, z]) >>> E.match(a*b) {a_: 2, b_: x**3*y*z} """ is_Wild = True __slots__ = ['exclude', 'properties'] def __new__(cls, name, exclude=(), properties=(), **assumptions): exclude = tuple([sympify(x) for x in exclude]) properties = tuple(properties) cls._sanitize(assumptions, cls) 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={}, old=False): 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__)
_range = _re.compile('([0-9]*:[0-9]+|[a-zA-Z]?:[a-zA-Z])')
[docs]def symbols(names, **args): r""" 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({'a', 'b', 'c'}) {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. Ranges are indicated by a colon and the type of range is determined by the character to the right of the colon. If the character is a digit then all contiguous digits to the left are taken as the nonnegative starting value (or 0 if there is no digit left of the colon) and all contiguous digits to the right are taken as 1 greater than the ending value:: >>> symbols('x:10') (x0, x1, x2, x3, x4, x5, x6, x7, x8, x9) >>> symbols('x5:10') (x5, x6, x7, x8, x9) >>> symbols('x5(:2)') (x50, x51) >>> 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)) If the character to the right of the colon is a letter, then the single letter to the left (or 'a' if there is none) is taken as the start and all characters in the lexicographic range *through* the letter to the right are used as the range:: >>> symbols('x:z') (x, y, z) >>> symbols('x:c') # null range () >>> symbols('x(:c)') (xa, xb, xc) >>> symbols(':c') (a, b, c) >>> symbols('a:d, x:z') (a, b, c, d, x, y, z) >>> symbols(('a:d', 'x:z')) ((a, b, c, d), (x, y, z)) Multiple ranges are supported; contiguous numerical ranges should be separated by parentheses to disambiguate the ending number of one range from the starting number of the next:: >>> symbols('x:2(1:3)') (x01, x02, x11, x12) >>> symbols(':3:2') # parsing is from left to right (00, 01, 10, 11, 20, 21) Only one pair of parentheses surrounding ranges are removed, so to include parentheses around ranges, double them. And to include spaces, commas, or colons, escape them with a backslash:: >>> symbols('x((a:b))') (x(a), x(b)) >>> symbols(r'x(:1\,:2)') # or r'x((:1)\,(:2))' (x(0,0), x(0,1)) All newly created symbols have assumptions set according 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 like 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 isinstance(names, string_types): marker = 0 literals = [r'\,', r'\:', r'\ '] for i in range(len(literals)): lit = literals.pop(0) if lit in names: while chr(marker) in names: marker += 1 lit_char = chr(marker) marker += 1 names = names.replace(lit, lit_char) literals.append((lit_char, lit[1:])) def literal(s): if literals: for c, l in literals: s = s.replace(c, l) return s names = names.strip() as_seq = names.endswith(',') if as_seq: names = names[:-1].rstrip() if not names: raise ValueError('no symbols given') # split on commas names = [n.strip() for n in names.split(',')] if not all(n for n in names): raise ValueError('missing symbol between commas') # split on spaces for i in range(len(names) - 1, -1, -1): names[i: i + 1] = names[i].split() 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(literal(name), **args) result.append(symbol) continue split = _range.split(name) # remove 1 layer of bounding parentheses around ranges for i in range(len(split) - 1): if i and ':' in split[i] and split[i] != ':' and \ split[i - 1].endswith('(') and \ split[i + 1].startswith(')'): split[i - 1] = split[i - 1][:-1] split[i + 1] = split[i + 1][1:] for i, s in enumerate(split): if ':' in s: if s[-1].endswith(':'): raise ValueError('missing end range') a, b = s.split(':') if b[-1] in string.digits: a = 0 if not a else int(a) b = int(b) split[i] = [str(c) for c in range(a, b)] else: a = a or 'a' split[i] = [string.ascii_letters[c] for c in range( string.ascii_letters.index(a), string.ascii_letters.index(b) + 1)] # inclusive if not split[i]: break else: split[i] = [s] else: seq = True if len(split) == 1: names = split[0] else: names = [''.join(s) for s in cartes(*split)] if literals: result.extend([cls(literal(s), **args) for s in names]) else: result.extend([cls(s, **args) for s in names]) if not seq and len(result) <= 1: if not result: return () 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:: Examples ======== >>> 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