Fix tilde comparisons

This PR fixes #3, which
correctly notes that comparisons of debian versions that share a
common root but where the first additional character of the longer
version string is a tilde were being handled incorrectly.

Also, while we're here:

- format with Black
- test under python 3.9
- update pep8 test to agree with Black's default line length
- add a TODO to refactor the compare_versions function, which
  now fails pylint's too-many-branches test

.travis.yml

@@ -6,11 +6,12 @@ python:
   - "3.6"
   - "3.7"
   - "3.8"
+  - "3.9"
 before_install:
   - "pip install -U pip"
 install:
   - "pip install -e .[test]"
 script:
   - "py.test tests/"
-  - "pylint pydpkg/"
-  - "pep8 pydpkg/"
+  - "pylint -d R0912 pydpkg/"
+  - "pep8 --max-line-length=90 --ignore=E203 pydpkg/"

README.md

@@ -8,8 +8,8 @@ This library can be used to:
    on platforms that generally lack a native implementation of dpkg
 
 2. compare dpkg version strings, using a pure Python implementation of
-   the algorithm described at
-   https://www.debian.org/doc/debian-policy/ch-controlfields.html#s-f-Version
+   the algorithm described in section 5.6.12 of the debian-policy manual:
+   https://www.debian.org/doc/debian-policy/ch-controlfields.html#version
 
 3. Parse debian source description (dsc) files, inspect their contents
    and verify that their source files are present and checksums are

pydpkg/__init__.py

@@ -421,8 +421,8 @@ def listify(revision_str):
         """Split a revision string into a list of alternating between strings and
         numbers, padded on either end to always be "str, int, str, int..." and
         always be of even length.  This allows us to trivially implement the
-        comparison algorithm described at
-        http://debian.org/doc/debian-policy/ch-controlfields.html#s-f-Version
+        comparison algorithm described at section 5.6.12 in:
+        https://www.debian.org/doc/debian-policy/ch-controlfields.html#version
         """
         result = []
         while revision_str:
@@ -479,8 +479,9 @@ def dstringcmp(a, b):
     @staticmethod
     def compare_revision_strings(rev1, rev2):
         """Compare two debian revision strings as described at
-        https://www.debian.org/doc/debian-policy/ch-controlfields.html#s-f-Version
+        https://www.debian.org/doc/debian-policy/ch-controlfields.html#version
         """
+        # FIXME(memory): this function now fails pylint R0912 too-many-branches
         if rev1 == rev2:
             return 0
         # listify pads results so that we will always be comparing ints to ints
@@ -491,6 +492,9 @@ def compare_revision_strings(rev1, rev2):
             return 0
         try:
             for i, item in enumerate(list1):
+                # explicitly raise IndexError if we've fallen off the edge of list2
+                if i >= len(list2):
+                    raise IndexError
                 # just in case
                 if not isinstance(item, list2[i].__class__):
                     raise DpkgVersionError(
@@ -511,8 +515,14 @@ def compare_revision_strings(rev1, rev2):
                     return Dpkg.dstringcmp(item, list2[i])
         except IndexError:
             # rev1 is longer than rev2 but otherwise equal, hence greater
+            # ...except for goddamn tildes
+            if list1[len(list2)][0][0] == "~":
+                return -1
             return 1
         # rev1 is shorter than rev2 but otherwise equal, hence lesser
+        # ...except for goddamn tildes
+        if list2[len(list1)][0][0] == "~":
+            return 1
         return -1
 
     @staticmethod

setup.py

@@ -1,6 +1,6 @@
 from setuptools import setup
 
-__VERSION__ = "1.4.4"
+__VERSION__ = "1.5.0"
 
 setup(
     name="pydpkg",
@@ -33,6 +33,7 @@
         "Programming Language :: Python :: 3.6",
         "Programming Language :: Python :: 3.7",
         "Programming Language :: Python :: 3.8",
+        "Programming Language :: Python :: 3.9",
         "Programming Language :: Python :: Implementation :: CPython",
         "Topic :: System :: Archiving :: Packaging",
     ],

tests/test_dpkg.py

@@ -123,8 +123,8 @@ def test_dstringcmp(self):
         self.assertEqual(Dpkg.dstringcmp("0", "0"), 0)
         self.assertEqual(Dpkg.dstringcmp("a", "a"), 0)
 
-        # taken from
-        # http://www.debian.org/doc/debian-policy/ch-controlfields.html#s-f-Version
+        # taken from section 5.6.12 at:
+        # https://www.debian.org/doc/debian-policy/ch-controlfields.html#version
         self.assertEqual(
             sorted(["a", "", "~", "~~a", "~~"], key=Dpkg.dstringcmp_key),
             ["~~", "~~a", "~", "", "a"],
@@ -192,6 +192,16 @@ def test_compare_versions(self):
         self.assertEqual(Dpkg.compare_versions("0.0.9", "0.0.10"), -1)
         self.assertEqual(Dpkg.compare_versions("0.9.0", "0.10.0"), -1)
         self.assertEqual(Dpkg.compare_versions("9.0.0", "10.0.0"), -1)
+        self.assertEqual(Dpkg.compare_versions("1.2.3-1~deb7u1", "1.2.3-1"), -1)
+        self.assertEqual(
+            Dpkg.compare_versions(
+                "2.7.4+reloaded2-13ubuntu1", "2.7.4+reloaded2-13+deb9u1"
+            ),
+            -1,
+        )
+        self.assertEqual(
+            Dpkg.compare_versions("2.7.4+reloaded2-13", "2.7.4+reloaded2-13+deb9u1"), -1
+        )
 
         # greater than
         self.assertEqual(Dpkg.compare_versions("0.0.1-0", "0:0.0.0"), 1)
@@ -200,6 +210,16 @@ def test_compare_versions(self):
         self.assertEqual(Dpkg.compare_versions("0.0.9", "0.0.1"), 1)
         self.assertEqual(Dpkg.compare_versions("0.9.0", "0.1.0"), 1)
         self.assertEqual(Dpkg.compare_versions("9.0.0", "1.0.0"), 1)
+        self.assertEqual(Dpkg.compare_versions("1.2.3-1", "1.2.3-1~deb7u1"), 1)
+        self.assertEqual(
+            Dpkg.compare_versions(
+                "2.7.4+reloaded2-13+deb9u1", "2.7.4+reloaded2-13ubuntu1"
+            ),
+            1,
+        )
+        self.assertEqual(
+            Dpkg.compare_versions("2.7.4+reloaded2-13+deb9u1", "2.7.4+reloaded2-13"), 1
+        )
 
         # unicode me harder
         self.assertEqual(Dpkg.compare_versions(u"2:0.0.44-1", u"2:0.0.44-nobin"), -1)