input: Write a function to create a Python function that takes a string containing a numerical expression and returns the result. The function should be named eval_expr and should use the eval function to evaluate the expression.
  assert eval_expr("2+3")==5
  assert eval_expr("10-4*2")==2
  assert eval_expr("5/2")==2.5
  assert eval_expr("(3+2)*4")==20
  assert eval_expr("7")==7
output: def eval_expr(expression):
      return eval(expression)