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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def extern_eval(self, context_handle, python_code_str_ptr, python_code_str_len):
 """Given an evalable string, eval it and return a Handle for its result."""

    c = self._ffi.from_handle(context_handle)
    return self.call(c, eval, [self.to_py_str(python_code_str_ptr, python_code_str_len)])