packaging: extract python exe info to own function

This is generic functionality. We'll need it for WIX.

As part of the port, we expose the full version and return
the data as a dict.

Differential Revision: https://phab.mercurial-scm.org/D6090

contrib/packaging/hgpackaging/inno.py

@@ -19,14 +19,10 b' from .util import ('
     extract_tar_to_directory,
     extract_zip_to_directory,
     find_vc_runtime_files,
+    python_exe_info,
 )
 
 
-PRINT_PYTHON_INFO = '''
-import platform, sys; print("%s:%d" % (platform.architecture()[0], sys.version_info[0]))
-'''.strip()
-
-
 def build(source_dir: pathlib.Path, build_dir: pathlib.Path,
           python_exe: pathlib.Path, iscc_exe: pathlib.Path,
           version=None):
@@ -50,23 +46,18 b' def build(source_dir: pathlib.Path, buil'
     # architecture.
     vc_x64 = r'\x64' in os.environ['LIB']
 
-    res = subprocess.run(
-        [str(python_exe), '-c', PRINT_PYTHON_INFO],
-        capture_output=True, check=True)
-
-    py_arch, py_version = res.stdout.decode('utf-8').split(':')
-    py_version = int(py_version)
+    py_info = python_exe_info(python_exe)
 
     if vc_x64:
-        if py_arch != '64bit':
+        if py_info['arch'] != '64bit':
             raise Exception('architecture mismatch: Visual C++ environment '
                             'is configured for 64-bit but Python is 32-bit')
     else:
-        if py_arch != '32bit':
+        if py_info['arch'] != '32bit':
             raise Exception('architecture mismatch: Visual C++ environment '
                             'is configured for 32-bit but Python is 64-bit')
 
-    if py_version != 2:
+    if py_info['py3']:
         raise Exception('Only Python 2 is currently supported')
 
     build_dir.mkdir(exist_ok=True)

contrib/packaging/hgpackaging/util.py

@@ -7,8 +7,10 b''
 
 # no-check-code because Python 3 native.
 
+import distutils.version
 import os
 import pathlib
+import subprocess
 import tarfile
 import zipfile
 
@@ -46,3 +48,26 b' def find_vc_runtime_files(x64=False):'
         d / 'msvcr90.dll',
         winsxs / 'Manifests' / ('%s.manifest' % version),
     ]
+
+
+PRINT_PYTHON_INFO = '''
+import platform; print("%s:%s" % (platform.architecture()[0], platform.python_version()))
+'''.strip()
+
+
+def python_exe_info(python_exe: pathlib.Path):
+    """Obtain information about a Python executable."""
+
+    res = subprocess.run(
+        [str(python_exe), '-c', PRINT_PYTHON_INFO],
+        capture_output=True, check=True)
+
+    arch, version = res.stdout.decode('utf-8').split(':')
+
+    version = distutils.version.LooseVersion(version)
+
+    return {
+        'arch': arch,
+        'version': version,
+        'py3': version >= distutils.version.LooseVersion('3'),
+    }