smichr/sympy — comment on commit a00f5e8c5ffec22f2a15acc2b105478cca9a6619
File:  line 0
By smichr:

OK, the sentence in the commit was edited:

An _eval_subs routine only needs to be written if more than just trying
the replacement on all the args of the object. For example,
Integrals need to watch out for the integration variables and not
allow certain changes to them. Many objects (especially in secondquant)
were essentially duplicating what is now the fallback behavior in _subs
(i.e. trying the substitution on all arguments) so they could be (and
were) removed.