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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 validate(self):
 """Ensure that the ConstructResult block is valid."""

        if not isinstance(self.fields, dict):
            raise TypeError(u'Expected dict fields, got: {} {}'.format(
                type(self.fields).__name__, self.fields))

        for key, value in six.iteritems(self.fields):
            validate_safe_string(key)
            if not isinstance(value, Expression):
                raise TypeError(
                    u'Expected Expression values in the fields dict, got: '
                    u'{} -> {}'.format(key, value))