1 files changed, 107 insertions, 0 deletions
diff --git a/python/mozbuild/mozbuild/pythonutil.py b/python/mozbuild/mozbuild/pythonutil.py
new file mode 100644
index 0000000000..00b2deef62
--- /dev/null
+++ b/python/mozbuild/mozbuild/pythonutil.py
@@ -0,0 +1,107 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+from __future__ import absolute_import, print_function, unicode_literals
+
+import os
+import six
+import subprocess
+import sys
+
+from distutils.version import StrictVersion
+
+
+def iter_modules_in_path(*paths):
+    paths = [os.path.abspath(os.path.normcase(p)) + os.sep for p in paths]
+    for name, module in sys.modules.items():
+        if getattr(module, "__file__", None) is None:
+            continue
+        if module.__file__ is None:
+            continue
+        path = module.__file__
+
+        if path.endswith(".pyc"):
+            path = path[:-1]
+        path = os.path.abspath(os.path.normcase(path))
+
+        if any(path.startswith(p) for p in paths):
+            yield path
+
+
+def python_executable_version(exe):
+    """Determine the version of a Python executable by invoking it.
+
+    May raise ``subprocess.CalledProcessError`` or ``ValueError`` on failure.
+    """
+    program = "import sys; print('.'.join(map(str, sys.version_info[0:3])))"
+    out = six.ensure_text(
+        subprocess.check_output([exe, "-c", program], universal_newlines=True)
+    ).rstrip()
+    return StrictVersion(out)
+
+
+def _find_python_executable(major):
+    if major not in (2, 3):
+        raise ValueError("Expected a Python major version of 2 or 3")
+    min_versions = {2: "2.7.0", 3: "3.6.0"}
+
+    def ret(min_version=min_versions[major]):
+        from mozfile import which
+
+        prefix = min_version[0] + "."
+        if not min_version.startswith(prefix):
+            raise ValueError(
+                "min_version expected a %sx string, got %s" % (prefix, min_version)
+            )
+
+        min_version = StrictVersion(min_version)
+        major = min_version.version[0]
+
+        if sys.version_info.major == major:
+            our_version = StrictVersion("%s.%s.%s" % (sys.version_info[0:3]))
+
+            if our_version >= min_version:
+                # This will potentially return a virtualenv Python. It's probably
+                # OK for now...
+                return sys.executable, our_version.version
+
+            # Else fall back to finding another binary.
+
+        # https://www.python.org/dev/peps/pep-0394/ defines how the Python binary
+        # should be named. `python3` should refer to some Python 3, and
+        # `python2` to some Python 2. `python` may refer to a Python 2 or 3.
+        # `pythonX.Y` may exist.
+        #
+        # Since `python` is ambiguous and `pythonX` should always exist, we
+        # ignore `python` here. We instead look for the preferred `pythonX` first
+        # and fall back to `pythonX.Y` if it isn't found or doesn't meet our
+        # version requirements.
+        names = ["python%d" % major]
+
+        # Look for `pythonX.Y` down to our minimum version.
+        for minor in range(9, min_version.version[1] - 1, -1):
+            names.append("python%d.%d" % (major, minor))
+
+        for name in names:
+            exe = which(name)
+            if not exe:
+                continue
+
+            # We always verify we can invoke the executable and its version is
+            # sane.
+            try:
+                version = python_executable_version(exe)
+            except (subprocess.CalledProcessError, ValueError):
+                continue
+
+            if version >= min_version:
+                return exe, version.version
+
+        return None, None
+
+    return ret
+
+
+find_python2_executable = _find_python_executable(2)
+find_python3_executable = _find_python_executable(3)