derived from it.  A</span>
<span class="sd">    class that has a metaclass derived from ABCMeta cannot be</span>
<span class="sd">    instantiated unless all of its abstract properties are overridden.</span>
<span class="sd">    The abstract properties can be called using any of the normal</span>
<span class="sd">    &#39;super&#39; call mechanisms.</span>

<span class="sd">    Usage:</span>

<span class="sd">        class C(metaclass=ABCMeta):</span>
<span class="sd">            @abstractproperty</span>
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