Comment #4 on issue 2566 by [email protected]: Equating Sums shouldn't
depend on dummy variables
http://code.google.com/p/sympy/issues/detail?id=2566
I'm increasingly against converting Symbols to Dummys internally. This
makes it impossible to do substitutions on the arguments. For example,
Lambda, which does do this (issue 2442):
In [84]: Lambda(y, 2*y).subs(y, x)
Out[84]: Λ(y, 2⋅y)
In [85]: Lambda(y, 2*y).subs(y, 1/y)
Out[85]: Λ(y, 2⋅y)
In [86]: Lambda(y, 2*y).xreplace({y, 1/y})
---------------------------------------------------------------------------
AttributeError Traceback (most recent call last)
/Users/aaronmeurer/Documents/Python/sympy/sympy/<ipython-input-86-da62efdbaba9>
in
<module>()
----> 1 Lambda(y, 2*y).xreplace({y, 1/y})
/Users/aaronmeurer/Documents/Python/sympy/sympy/sympy/core/basic.py in
xreplace(self, rule)
899
900 @deprecated
--> 901 def __contains__(self, obj):
902 if self == obj:
903 return True
/Users/aaronmeurer/Documents/Python/sympy/sympy/sympy/core/basic.py in
xreplace(self, rule)
899
900 @deprecated
--> 901 def __contains__(self, obj):
902 if self == obj:
903 return True
/Users/aaronmeurer/Documents/Python/sympy/sympy/sympy/core/basic.py in
xreplace(self, rule)
1343
1344 @deprecated
-> 1345 def __contains__(self, obj):
1346 return (self == obj)
1347
AttributeError: 'set' object has no attribute 'get'
The only way to change it is to manually rewrite the Lambda. See also
issue 2571, which has real life examples of why this sort of thing would be
useful for Integral.
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