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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 virt_env(self):
 """ Getter for this instance's virt env, creates it if needed Returns: lago.virt.VirtEnv: virt env instance used by this prefix """

        if self._virt_env is None:
            self._virt_env = self._create_virt_env()
        return self._virt_env