I'm trying to fix sympy.vector.Point so that it follows the args
invariant. Right now, there is a check that the parent_point must be a
Point instance, but it can also be None, in which case, it is set to a
Symbol. This causes a Point constructed in such way to not follow
expr.func(*expr.args) == expr.
Example:
In [11]: from sympy.vector import *
In [12]: C = CoordSysCartesian('C')
In [13]: C.origin.func(*C.origin.args)
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-13-e75fb47c767f> in <module>()
----> 1 C.origin.func(*C.origin.args)
/Users/aaronmeurer/Documents/Python/sympy/sympy-scratch/sympy/vector/point.py
in __new__(cls, name, position, parent_point)
19 if (not isinstance(parent_point, Point)
20 and parent_point is not None):
---> 21 raise TypeError("parent_point should be a Point instance")
22 #Create an object
23 if parent_point is None:
TypeError: parent_point should be a Point instance
I don't know how to fix this because I don't know what the
parent_point should be set to in this case (I'm not completely clear
on the mathematics there).
THIS IS BLOCKING THE RELEASE, SO IMMEDIATE HELP WOULD BE APPRECIATED.
As a side note, the fact that this sort of thing exists in SymPy is
embarrassingly bad. We should fix test_args to test that objects are
recreatable from their arguments and put a moratorium on new objects
that don't follow that rule.
Aaron Meurer
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