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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 list(cls, datacenter=None):
 """List virtual machine vlan (in the future it should also handle PaaS vlan)."""

        options = {}
        if datacenter:
            datacenter_id = int(Datacenter.usable_id(datacenter))
            options['datacenter_id'] = datacenter_id

        return cls.call('hosting.vlan.list', options)