evalf behaves differently for E**x and exp(x)

[G B]

Hi-- 

exp() doesn't seem to evalf its arguments when evalf is called on it.  This is probably a bug, and if so I'll file an issue.  In the mean time, is there an easy way to get sympy to convert exp(x) expressions to E**x expressions?

exp(t*sqrt(5)).n()  -> exp(t*sqrt(5))

E**(t*sqrt(5)).n() -> E**(2.23606797749979*t)

I think this is causing me some trouble when converting complex expressions to numpy via lambdify.  I'm trying to lambdify a result from dsolve that includes square roots of very large integers (not sure where those large integers are coming from).  When I try to execute the result, I get "AttributeError: 'int' object has no attribute 'sqrt'".

I'll see if I can get the lambdify to trip up with a simple set of inputs.  Right now this is the culmination of a 100 cell IPython notebook...

[Aaron Meurer]

Seems like another thing that
https://github.com/sympy/sympy/issues/4898 would fix. I think the only
way to create E**x is to use Pow(E, x, evaluate=False).

The lambdify thing might be a separate bug.

Aaron Meurer

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[G B]

If I'm understanding my problem correctly, I think I actually want it to evaluate...  Is there a way to ask sympy to find all occurrences of exp() in an expression and replace them with Pow(E,...) or E**?

I've tried messing with replace, but I'm not sure I've got the syntax right...

Alternatively, can I force evalf to drill down into the exp() arguments?

[Aaron Meurer]

You have to do evaluate=False because Pow(E, x) is automatically
converted to exp() otherwise.

You can use something like expr.replace(exp, lambda x: Pow(E, x,
evaluate=False)).

Aaron Meurer

> https://groups.google.com/d/msgid/sympy/20ecfb7f-0284-4f69-9d0e-4bd8cb21dbbe%40googlegroups.com.

[G B]

Hey Aaron--

This bug came up to bite me again, so I tried your work around.  The replace you suggested doesn't work (I get the same result back).

What does seem to work is expr.replace(exp, lambda x: Pow(E, N(x)))

That forces the evaluation of the argument to exp, and then carries on.  

Thanks--