From d2b5be9a0627e38d2280ef865dab3e74b7d2bde4 Mon Sep 17 00:00:00 2001
From: Christophe Vu-Brugier <cvubrugier@fastmail.fm>
Date: Wed, 23 Dec 2015 11:46:14 +0100
Subject: [PATCH] Add importlib fix for PEP 3147 issue

Python 3 has a new standard for installing .pyc file, called PEP
3147. Unfortunately, this standard requires both the .py and .pyc
files to be installed for a Python module to be found. This is quite
annoying on space-constrained embedded systems, since the .py file is
technically not required for execution.

This patch changes cache_from_source() and source_from_cache() in
importlib to get rid of the "__pycache__" directory.
This effectively disables PEP 3147 for:

* The python standard library
* Packages built with distutils or setuptools
* Packages built with automake that use the `py-compile` helper

Signed-off-by: Christophe Vu-Brugier <cvubrugier@fastmail.fm>
---
 Lib/importlib/_bootstrap_external.py | 37 +++++-------------------------------
 1 file changed, 5 insertions(+), 32 deletions(-)

diff --git a/Lib/importlib/_bootstrap_external.py b/Lib/importlib/_bootstrap_external.py
index 616b17f..e30129c 100644
--- a/Lib/importlib/_bootstrap_external.py
+++ b/Lib/importlib/_bootstrap_external.py
@@ -255,8 +255,6 @@ def cache_from_source(path, debug_override=None, *, optimization=None):
     a True value is the same as setting 'optimization' to the empty string
     while a False value is equivalent to setting 'optimization' to '1'.
 
-    If sys.implementation.cache_tag is None then NotImplementedError is raised.
-
     """
     if debug_override is not None:
         _warnings.warn('the debug_override parameter is deprecated; use '
@@ -267,10 +265,7 @@ def cache_from_source(path, debug_override=None, *, optimization=None):
         optimization = '' if debug_override else 1
     head, tail = _path_split(path)
     base, sep, rest = tail.rpartition('.')
-    tag = sys.implementation.cache_tag
-    if tag is None:
-        raise NotImplementedError('sys.implementation.cache_tag is None')
-    almost_filename = ''.join([(base if base else rest), sep, tag])
+    almost_filename = ''.join([(base if base else rest)])
     if optimization is None:
         if sys.flags.optimize == 0:
             optimization = ''
@@ -281,39 +276,17 @@ def cache_from_source(path, debug_override=None, *, optimization=None):
         if not optimization.isalnum():
             raise ValueError('{!r} is not alphanumeric'.format(optimization))
         almost_filename = '{}.{}{}'.format(almost_filename, _OPT, optimization)
-    return _path_join(head, _PYCACHE, almost_filename + BYTECODE_SUFFIXES[0])
+    return _path_join(head, almost_filename + BYTECODE_SUFFIXES[0])
 
 
 def source_from_cache(path):
     """Given the path to a .pyc. file, return the path to its .py file.
 
     The .pyc file does not need to exist; this simply returns the path to
-    the .py file calculated to correspond to the .pyc file.  If path does
-    not conform to PEP 3147/488 format, ValueError will be raised. If
-    sys.implementation.cache_tag is None then NotImplementedError is raised.
-
+    the .py file calculated to correspond to the .pyc file.
     """
-    if sys.implementation.cache_tag is None:
-        raise NotImplementedError('sys.implementation.cache_tag is None')
-    head, pycache_filename = _path_split(path)
-    head, pycache = _path_split(head)
-    if pycache != _PYCACHE:
-        raise ValueError('{} not bottom-level directory in '
-                         '{!r}'.format(_PYCACHE, path))
-    dot_count = pycache_filename.count('.')
-    if dot_count not in {2, 3}:
-        raise ValueError('expected only 2 or 3 dots in '
-                         '{!r}'.format(pycache_filename))
-    elif dot_count == 3:
-        optimization = pycache_filename.rsplit('.', 2)[-2]
-        if not optimization.startswith(_OPT):
-            raise ValueError("optimization portion of filename does not start "
-                             "with {!r}".format(_OPT))
-        opt_level = optimization[len(_OPT):]
-        if not opt_level.isalnum():
-            raise ValueError("optimization level {!r} is not an alphanumeric "
-                             "value".format(optimization))
-    base_filename = pycache_filename.partition('.')[0]
+    head, filename = _path_split(path)
+    base_filename = filename.partition('.')[0]
     return _path_join(head, base_filename + SOURCE_SUFFIXES[0])
 
 
-- 
2.6.4