[PATCH 8/8] Use the fallback data file if we're not installed on a Debian system.

[Ben Finney]

---
 debian/changelog             |  1 +
 lib/debian/debian_support.py | 36 ++++++++++++++++++++++++++++++++++--
 2 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/debian/changelog b/debian/changelog
index aae87cf1..e3daff7c 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -5,6 +5,7 @@ python-debian (0.1.30) UNRELEASED; urgency=medium
   * Include the data for Debian releases in the Python distribution build.
   * Use Debian ‘distro_info’ API for Debian versions and release names.
     Closes: bug#849058. Thanks to Paul Gevers for the report.
+  * Use the fallback data file if we're not installed on a Debian system.
 
  --
 
diff --git a/lib/debian/debian_support.py b/lib/debian/debian_support.py
index 200fbfd1..31884efe 100644
--- a/lib/debian/debian_support.py
+++ b/lib/debian/debian_support.py
@@ -24,12 +24,17 @@
 
 from __future__ import absolute_import, print_function
 
+import csv
 import os
 import re
 import types
 
+try:
+    import distro_info
+except ImportError:
+    distro_info = NotImplemented
+
 from debian.deprecation import function_deprecated_by
-import distro_info
 
 try:
     import apt_pkg
@@ -56,6 +61,15 @@ except ImportError:
                     " implementation because it depends on OpenSSL, which"
                     " may not be linked with this library due to license"
                     " incompatibilities")
+try:
+    # Python 3.3 or later.
+    from types import SimpleNamespace
+except ImportError:
+    class SimpleNamespace(object):
+        """ A simple namespace for attributes. """
+
+import pkg_resources
+
 
 class ParseError(Exception):
     """An exception which is used to signal a parse failure.
@@ -418,7 +432,25 @@ class PseudoEnum:
 class Release(PseudoEnum): pass
 
 
-debian_distro_info = distro_info.DebianDistroInfo()
+if distro_info is NotImplemented:
+    # The `distro_info` package is specific to a Debian release; it is
+    # not available on PyPI. We need to fall back on the installed
+    # data file resource in this Python distribution.
+    _python_distribution = pkg_resources.get_distribution("python-debian")
+    if not pkg_resources.resource_exists('debian', 'releases.csv'):
+        raise RuntimeError("Debian releases data not available on this system")
+    _releases_data_infile = pkg_resources.resource_stream(
+            'debian', 'releases.csv')
+    debian_distro_info = SimpleNamespace()
+    with _releases_data_infile:
+        _releases_data_reader = csv.DictReader(_releases_data_infile)
+        debian_distro_info.all = [
+                record['codename'].lower() for record in _releases_data_reader]
+    del _releases_data_reader
+    del _releases_data_infile
+    del _python_distribution
+else:
+    debian_distro_info = distro_info.DebianDistroInfo()
 
 def list_releases():
     releases = {
-- 
2.11.0

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