compression: Prevent using incompatible 'lzma' module from pyliblzma

Try importing the 'lzma' module only in Python 3.3+, that is versions
known to have it built-in. This way, we can prevent accidentally
importing incompatible module using the same name, e.g. pyliblzma.

Bug: https://bugs.gentoo.org/643254

2 files changed, 13 insertions, 4 deletions

diff --git a/gemato/compression.py b/gemato/compression.py
index 11ede67..145c0bf 100644
--- a/gemato/compression.py
+++ b/gemato/compression.py
@@ -1,6 +1,6 @@
 # gemato: compressed file support
 # vim:fileencoding=utf-8
-# (c) 2017 Michał Górny
+# (c) 2017-2018 Michał Górny
 # Licensed under the terms of 2-clause BSD license
 
 import gzip
@@ -18,9 +18,12 @@ else:
     except ImportError:
         bz2 = None
 
-try:
+# Python 3.3+ has a built-in lzma module. Older versions may have
+# an incompatible external module of the same name, so explicitly
+# force using the backport there.
+if sys.hexversion >= 0x03030000:
     import lzma
-except ImportError:
+else:
     try:
         import backports.lzma as lzma
     except ImportError:
diff --git a/tox.ini b/tox.ini
index 45f7ce7..7acc9c3 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,5 +1,5 @@
 [tox]
-envlist = begin,py27,py34,py35,py36,pypy,pypy3,nodeps,end
+envlist = begin,py27,py34,py35,py36,pypy,pypy3,incompatible-lzma,nodeps,end
 # we operate on sources anyway
 skipsdist = True
 
@@ -54,6 +54,12 @@ basepython = python2.7
 deps =
 	coverage
 
+[testenv:incompatible-lzma]
+basepython = python2.7
+deps =
+	coverage
+	pyliblzma
+
 [testenv]
 commands = coverage run -p -m unittest discover -v