Issue 25295: functools.lru_cache raises KeyError (original) (raw)

The SymPy project (https://github.com/sympy/sympy) makes heavy use of caching to speed up the creation of symbols and expressions. If available, we make use of the fastcache library (https://github.com/pbrady/fastcache) - an lru_cache written in C. Otherwise we use lru_cache provided by functools. When testing with 3.5, we started to observe KeyErrors coming from the new lru_cache implementation in _functoolsmodule.c. There was some discussion on this on the SymPy mailing list here https://groups.google.com/forum/#!topic/sympy/AnwYTJGRBB4.

Here's an example of the failure in the SymPy test suite (Note that this failure does not occur if we use the lru_cache in 3.4 or fastcache or if we use the lru_cache in 3.5 with no size limit)

$ /usr/local/opt/python-3.5/bin/python3 Python 3.5.0 (default, Oct 1 2015, 21:51:43) [GCC 5.1.1 20150618 (Red Hat 5.1.1-4)] on linux Type "help", "copyright", "credits" or "license" for more information.

from sympy import test test("test_frame.py") ============================= test process starts ============================== executable: /usr/local/opt/python-3.5/bin/python3 (3.5.0-final-0) [CPython] architecture: 64-bit cache: yes ground types: python random seed: 7625225 hash randomization: on (PYTHONHASHSEED=2787593824)

sympy/physics/vector/tests/test_frame.py[4] .EE. [FAIL]

____________ sympy/physics/vector/tests/test_frame.py:test_ang_vel _____________ File "/home/peter/.local/lib/python3.5/site-packages/sympy/physics/vector/tests/test_frame.py", line 66, in test_ang_vel B = A.orientnew('B', 'Axis', [q2, A.x]) File "/home/peter/.local/lib/python3.5/site-packages/sympy/physics/vector/frame.py", line 640, in orientnew newframe.orient(self, rot_type, amounts, rot_order) File "/home/peter/.local/lib/python3.5/site-packages/sympy/physics/vector/frame.py", line 523, in orient [-axis[1], axis[0], 0]]) * sin(theta) + axis * axis.T) File "/home/peter/.local/lib/python3.5/site-packages/sympy/core/cache.py", line 93, in wrapper retval = cfunc(*args, **kwargs) File "/home/peter/.local/lib/python3.5/site-packages/sympy/core/function.py", line 375, in new result = super(Function, cls).new(cls, *args, **options) File "/home/peter/.local/lib/python3.5/site-packages/sympy/core/cache.py", line 93, in wrapper retval = cfunc(*args, **kwargs) File "/home/peter/.local/lib/python3.5/site-packages/sympy/core/function.py", line 199, in new evaluated = cls.eval(*args) File "/home/peter/.local/lib/python3.5/site-packages/sympy/functions/elementary/trigonometric.py", line 459, in eval if arg.could_extract_minus_sign(): File "/home/peter/.local/lib/python3.5/site-packages/sympy/core/expr.py", line 2047, in could_extract_minus_sign negative_self = -self File "/home/peter/.local/lib/python3.5/site-packages/sympy/core/expr.py", line 113, in neg return Mul(S.NegativeOne, self) File "/home/peter/.local/lib/python3.5/site-packages/sympy/core/cache.py", line 93, in wrapper retval = cfunc(*args, *kwargs) KeyError: (<class 'sympy.core.mul.Mul'>, 1, B_y, sin(2q(t)), <class 'sympy.core.assumptions.ManagedProperties'>, <class 'sympy.core.numbers.One'>, <class 'sympy.physics.vector.frame.CoordinateSym'>, sin)

______________ sympy/physics/vector/tests/test_frame.py:test_dcm _______________ File "/home/peter/.local/lib/python3.5/site-packages/sympy/physics/vector/tests/test_frame.py", line 131, in test_dcm B = A.orientnew('B', 'Axis', [q2, A.x]) File "/home/peter/.local/lib/python3.5/site-packages/sympy/physics/vector/frame.py", line 640, in orientnew newframe.orient(self, rot_type, amounts, rot_order) File "/home/peter/.local/lib/python3.5/site-packages/sympy/physics/vector/frame.py", line 523, in orient [-axis[1], axis[0], 0]]) * sin(theta) + axis * axis.T) File "/home/peter/.local/lib/python3.5/site-packages/sympy/core/cache.py", line 93, in wrapper retval = cfunc(*args, **kwargs) File "/home/peter/.local/lib/python3.5/site-packages/sympy/core/function.py", line 375, in new result = super(Function, cls).new(cls, *args, **options) File "/home/peter/.local/lib/python3.5/site-packages/sympy/core/cache.py", line 93, in wrapper retval = cfunc(*args, **kwargs) File "/home/peter/.local/lib/python3.5/site-packages/sympy/core/function.py", line 199, in new evaluated = cls.eval(*args) File "/home/peter/.local/lib/python3.5/site-packages/sympy/functions/elementary/trigonometric.py", line 459, in eval if arg.could_extract_minus_sign(): File "/home/peter/.local/lib/python3.5/site-packages/sympy/core/expr.py", line 2050, in could_extract_minus_sign (negative_self).extract_multiplicatively(-1) is not None) File "/home/peter/.local/lib/python3.5/site-packages/sympy/core/expr.py", line 1859, in extract_multiplicatively quotient = self / c File "/home/peter/.local/lib/python3.5/site-packages/sympy/core/decorators.py", line 77, in __sympifyit_wrapper return func(a, b) File "/home/peter/.local/lib/python3.5/site-packages/sympy/core/decorators.py", line 118, in binary_op_wrapper return func(self, other) File "/home/peter/.local/lib/python3.5/site-packages/sympy/core/expr.py", line 161, in div return Mul(self, Pow(other, S.NegativeOne)) File "/home/peter/.local/lib/python3.5/site-packages/sympy/core/cache.py", line 93, in wrapper retval = cfunc(*args, *kwargs) KeyError: (<class 'sympy.core.mul.Mul'>, B_x, -cos(2q(t)) + 1, <class 'sympy.core.assumptions.ManagedProperties'>, <class 'sympy.physics.vector.frame.CoordinateSym'>, <class 'sympy.core.add.Add'>)

=========== tests finished: 2 passed, 2 exceptions, in 1.57 seconds ============ DO NOT COMMIT! False

Sadly, I don't have a simplified test case to reproduce the error. I would be happy to try some debugging suggestions.

Thanks, Peter.