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
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.iterables import cartes
from sympy.utilities.exceptions import SymPyDeprecationWarning
import string
import re as _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 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
for key in assumptions.keys():
assumptions[key] = bool(assumptions[key])
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
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.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
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() #doctest: +SKIP
_Dummy_10
"""
_count = 0
__slots__ = ['dummy_index']
is_Dummy = True
def __new__(cls, name=None, **assumptions):
if name is None:
name = "Dummy_" + 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):
"""
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}
"""
__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={}, 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):
"""
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.
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 continguous digits to the left are taken as the nonnegative
starting value (or 0 if there are no digit 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('x(:1\,:2)') # or '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 = ['\,', '\:', '\ ']
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::
>>> 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
