From e2ea659eac1849db471d3c01a0d0af9d6fca2e9a Mon Sep 17 00:00:00 2001
From: Christophe Vu-Brugier <cvubrugier@fastmail.fm>
Date: Wed, 22 Feb 2017 16:48:49 -0800
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>
[ Andrey Smirnov: ported to Python 3.6 ]
Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
---
 Lib/importlib/_bootstrap_external.py | 44 ++++------------------------
 1 file changed, 5 insertions(+), 39 deletions(-)

diff --git a/Lib/importlib/_bootstrap_external.py b/Lib/importlib/_bootstrap_external.py
index 25a3f8c0e0..2cb9a9aa52 100644
--- a/Lib/importlib/_bootstrap_external.py
+++ b/Lib/importlib/_bootstrap_external.py
@@ -313,8 +313,6 @@ 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 '
@@ -326,10 +324,7 @@ def cache_from_source(path, debug_override=None, *, optimization=None):
     path = _os.fspath(path)
     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 = ''
@@ -366,46 +361,17 @@ def cache_from_source(path, debug_override=None, *, optimization=None):
             head.lstrip(path_separators),
             filename,
         )
-    return _path_join(head, _PYCACHE, filename)
+    return _path_join(head, filename)
 
 
 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')
-    path = _os.fspath(path)
-    head, pycache_filename = _path_split(path)
-    found_in_pycache_prefix = False
-    if sys.pycache_prefix is not None:
-        stripped_path = sys.pycache_prefix.rstrip(path_separators)
-        if head.startswith(stripped_path + path_sep):
-            head = head[len(stripped_path):]
-            found_in_pycache_prefix = True
-    if not found_in_pycache_prefix:
-        head, pycache = _path_split(head)
-        if pycache != _PYCACHE:
-            raise ValueError(f'{_PYCACHE} not bottom-level directory in '
-                             f'{path!r}')
-    dot_count = pycache_filename.count('.')
-    if dot_count not in {2, 3}:
-        raise ValueError(f'expected only 2 or 3 dots in {pycache_filename!r}')
-    elif dot_count == 3:
-        optimization = pycache_filename.rsplit('.', 2)[-2]
-        if not optimization.startswith(_OPT):
-            raise ValueError("optimization portion of filename does not start "
-                             f"with {_OPT!r}")
-        opt_level = optimization[len(_OPT):]
-        if not opt_level.isalnum():
-            raise ValueError(f"optimization level {optimization!r} is not an "
-                             "alphanumeric value")
-    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])
 
 
-- 
2.25.1