Actually add the tool!

pex/tools/commands/interpreter.py

@@ -0,0 +1,93 @@
+# Copyright 2020 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+from __future__ import absolute_import
+
+import logging
+from argparse import ArgumentParser, Namespace
+
+from pex import pex_bootstrapper
+from pex.interpreter import PythonInterpreter
+from pex.interpreter_constraints import UnsatisfiableInterpreterConstraintsError
+from pex.pex import PEX
+from pex.tools.command import Command, Error, JsonMixin, Ok, OutputMixin, Result
+from pex.typing import TYPE_CHECKING
+from pex.variables import ENV
+
+if TYPE_CHECKING:
+    from typing import Iterator
+
+logger = logging.getLogger(__name__)
+
+
+class Interpreter(JsonMixin, OutputMixin, Command):
+    """Prints the path of the preferred interpreter to run the given PEX file with, if any."""
+
+    def add_arguments(self, parser):
+        # type: (ArgumentParser) -> None
+        self.add_output_option(parser, entity="Python interpreter path"),
+        parser.add_argument(
+            "-a",
+            "--all",
+            action="store_true",
+            help="Print all compatible interpreters, preferred first.",
+        )
+        parser.add_argument(
+            "-v",
+            "--verbose",
+            action="store_true",
+            help="Print the interpreter requirement in addition to it's path.",
+        )
+        self.add_json_options(parser, entity="verbose output"),
+
+    @staticmethod
+    def _find_interpreters(
+        pex,  # type: PEX
+        all=False,  # type: bool
+    ):
+        # type: (...) -> Iterator[PythonInterpreter]
+        if not all:
+            yield pex.interpreter
+            return
+
+        if ENV.PEX_PYTHON:
+            logger.warning(
+                "Ignoring PEX_PYTHON={} in order to scan for all compatible "
+                "interpreters.".format(ENV.PEX_PYTHON)
+            )
+        for interpreter in pex_bootstrapper.iter_compatible_interpreters(
+            path=ENV.PEX_PYTHON_PATH,
+            interpreter_constraints=pex.pex_info().interpreter_constraints,
+        ):
+            yield interpreter
+
+    def run(
+        self,
+        pex,  # type: PEX
+        options,  # type: Namespace
+    ):
+        # type: (...) -> Result
+        if options.indent and not options.verbose:
+            logger.warning(
+                "Ignoring --indent={} since --verbose mode is not enabled.".format(options.indent)
+            )
+        with self.output(options) as out:
+            try:
+                for interpreter in self._find_interpreters(pex, all=options.all):
+                    if options.verbose:
+                        self.dump_json(
+                            options,
+                            {
+                                "path": interpreter.binary,
+                                "requirement": str(interpreter.identity.requirement),
+                                "platform": str(interpreter.platform),
+                            },
+                            out,
+                        )
+                    else:
+                        out.write(interpreter.binary)
+                    out.write("\n")
+            except UnsatisfiableInterpreterConstraintsError as e:
+                return Error(str(e))
+
+        return Ok()