converting to sympy [closed]

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Dear All

I would like to convert a sage equation to sympy, eg

x=var('x') y=2*x+Ei(x) y._sympy_()

... and get complains that Ei is not defined in sympy.

How can I define a (possibly fake) Ei function in sympy from sage? Or is there any other way to avoid the problem?

Thanks

Valery