Unexpected weakness in sympy substitution

[Coleman Broaddus]

Sympy's subs function does not seem to be able to recognize negative multi-term expressions...

x,y = symbols('x,y')

e1_, e2_ = symbols('e1, e2')

e1 = x

e2 = 1+x

[(e1).subs(e1,e1_), (-e1).subs(e1,e1_), (e2).subs(e2,e2_), (-e2).subs(e2,e2_)]

produces:

[e₁, -e₁, e₂, -x - 1]

Is there a reason why this can't or shouldn't be done?

[Mateusz Paprocki]

Hi,

This was a bug in SymPy 0.7.1 and before. It's fixed in git version (see http://github.com/sympy/sympy) and will be part of 0.7.2 release.

 

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Mateusz