use get_python_info for consistency and caching

docs/changelog/1462.misc.rst

@@ -0,0 +1 @@
+improve performance with internal lookup of Python version information - by :user:`blueyed`

src/tox/interpreters/__init__.py

@@ -5,7 +5,8 @@
 
 import tox
 from tox import reporter
-from tox.constants import SITE_PACKAGE_QUERY_SCRIPT, VERSION_QUERY_SCRIPT
+from tox.constants import SITE_PACKAGE_QUERY_SCRIPT
+from tox.interpreters.via_path import get_python_info
 
 
 class Interpreters:
@@ -56,7 +57,7 @@ def get_sitepackagesdir(self, info, envdir):
 def run_and_get_interpreter_info(name, executable):
     assert executable
     try:
-        result = exec_on_interpreter(str(executable), VERSION_QUERY_SCRIPT)
+        result = get_python_info(str(executable))
         result["version_info"] = tuple(result["version_info"])  # fix json dump transformation
         del result["name"]
         del result["version"]

src/tox/interpreters/via_path.py

@@ -35,7 +35,7 @@ def exe_spec(python_exe, base):
         python_exe = str(python_exe)
     with _SPECK_LOCK[python_exe]:
         if python_exe not in _SPECS:
-            info = get_python_info([python_exe])
+            info = get_python_info(python_exe)
             if info is not None:
                 found = PythonSpec(
                     info["name"],
@@ -51,9 +51,16 @@ def exe_spec(python_exe, base):
     return _SPECS[python_exe]
 
 
+_python_info_cache = {}
+
+
 def get_python_info(cmd):
+    try:
+        return _python_info_cache[cmd].copy()
+    except KeyError:
+        pass
     proc = subprocess.Popen(
-        cmd + [VERSION_QUERY_SCRIPT],
+        [cmd] + [VERSION_QUERY_SCRIPT],
         stdout=subprocess.PIPE,
         stderr=subprocess.PIPE,
         universal_newlines=True,
@@ -65,7 +72,8 @@ def get_python_info(cmd):
         except ValueError as exception:
             failure = exception
         else:
-            return result
+            _python_info_cache[cmd] = result
+            return result.copy()
     else:
         failure = "exit code {}".format(proc.returncode)
     reporter.verbosity1("{!r} cmd {!r} out {!r} err {!r} ".format(failure, cmd, out, err))

src/tox/logs/env.py

@@ -1,9 +1,6 @@
 from __future__ import absolute_import, unicode_literals
 
-import json
-import subprocess
-
-from tox.constants import VERSION_QUERY_SCRIPT
+from tox.interpreters.via_path import get_python_info
 
 from .command import CommandLog
 
@@ -17,9 +14,7 @@ def __init__(self, result_log, name, dict):
         self.dict = dict
 
     def set_python_info(self, python_executable):
-        cmd = [str(python_executable), VERSION_QUERY_SCRIPT]
-        result = subprocess.check_output(cmd, universal_newlines=True)
-        answer = json.loads(result)
+        answer = get_python_info(str(python_executable))
         answer["executable"] = python_executable
         self.dict["python"] = answer