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Lib/site-packages/virtualenv/discovery/discover.py

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+from __future__ import absolute_import, unicode_literals
+
+from abc import ABCMeta, abstractmethod
+
+from six import add_metaclass
+
+
+@add_metaclass(ABCMeta)
+class Discover(object):
+    """Discover and provide the requested Python interpreter"""
+
+    @classmethod
+    def add_parser_arguments(cls, parser):
+        """Add CLI arguments for this discovery mechanisms.
+
+        :param parser: the CLI parser
+        """
+        raise NotImplementedError
+
+    # noinspection PyUnusedLocal
+    def __init__(self, options):
+        """Create a new discovery mechanism.
+
+        :param options: the parsed options as defined within :meth:`add_parser_arguments`
+        """
+        self._has_run = False
+        self._interpreter = None
+
+    @abstractmethod
+    def run(self):
+        """Discovers an interpreter.
+
+
+        :return: the interpreter ready to use for virtual environment creation
+        """
+        raise NotImplementedError
+
+    @property
+    def interpreter(self):
+        """
+        :return: the interpreter as returned by :meth:`run`, cached
+        """
+        if self._has_run is False:
+            self._interpreter = self.run()
+            self._has_run = True
+        return self._interpreter