[python-debian/master] Support installation together with older versions of python-apt

[John Wright]

The deb822 module only uses apt_pkg for its TagFile interface, which is
only supported in later versions of python-apt.  But it's simple enough
to detect whether TagFile is available and fall back to the native
parser, rather than conflicting with earlier versions of python-apt.

Original patch by Jelmer Vernooij.

Closes: #590805
---
 debian/changelog     |    7 +++++++
 debian/control       |    4 ++--
 lib/debian/deb822.py |    4 +++-
 3 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/debian/changelog b/debian/changelog
index 7e1188a..5d164a5 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,3 +1,10 @@
+python-debian (0.1.18) UNRELEASED; urgency=low
+
+  * Support installation together with older versions of python-apt.
+    Original patch by Jelmer Vernooij. (Closes: #590805)
+
+ -- John Wright <jsw at debian.org>  Sun, 01 Aug 2010 01:01:41 -0700
+
 python-debian (0.1.17) unstable; urgency=low
 
   [ James Westby ]
diff --git a/debian/control b/debian/control
index d52ab3e..e8ad071 100644
--- a/debian/control
+++ b/debian/control
@@ -20,10 +20,10 @@ Depends: ${python:Depends}, ${misc:Depends}, python-chardet
 Recommends: python-apt
 Suggests: gpgv
 Provides: python-deb822
-Conflicts: python-deb822, python-apt (<< 0.7.94~)
+Conflicts: python-deb822
 Replaces: python-deb822
 Description: Python modules to work with Debian-related data formats
- This package provides Python modules that abstract many formats of Debian 
+ This package provides Python modules that abstract many formats of Debian
  related files. Currently handled are:
   * Debtags information (debian.debtags module)
   * debian/changelog (debian.changelog module)
diff --git a/lib/debian/deb822.py b/lib/debian/deb822.py
index 1a21e62..a0cad69 100644
--- a/lib/debian/deb822.py
+++ b/lib/debian/deb822.py
@@ -26,8 +26,10 @@ from deprecation import function_deprecated_by
 
 try:
     import apt_pkg
+    # This module uses apt_pkg only for its TagFile interface.
+    apt_pkg.TagFile
     _have_apt_pkg = True
-except ImportError:
+except (ImportError, AttributeError):
     _have_apt_pkg = False
 
 import chardet
-- 
1.7.1