TypeError: unsupported operand type(s) for ** or pow(): 'list' and 'sage.symbolic.expression.Expression'

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When I enter following command in Sage Notebook;

var('x k w')
f = x^3 * e^(k*x) * sin(w*x)
show(f)
show(f.diff(x))

I get this error

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-12-e1add3252393> in <module>()
      1 var('x k w')
----> 2 f = x**Integer(3) * e**(k*x) * sin(w*x)
      3 show(f)
      4 show(f.diff(x))

TypeError: unsupported operand type(s) for ** or pow(): 'list' and 'sage.symbolic.expression.Expression'

How can I resolve this issue.