From 4d89718930066e3e6ae0128a4816bbc3404554fb Mon Sep 17 00:00:00 2001
From: Brad Warren <bmw@eff.org>
Date: Fri, 23 Oct 2020 12:42:45 -0700
Subject: [PATCH] Use <= to "pin" dnspython

---
 tools/dev_constraints.txt   |  8 +++++++-
 tools/merge_requirements.py | 23 +++++++++++++++--------
 2 files changed, 22 insertions(+), 9 deletions(-)

diff --git a/tools/dev_constraints.txt b/tools/dev_constraints.txt
index fe7ab1e17..967596ded 100644
--- a/tools/dev_constraints.txt
+++ b/tools/dev_constraints.txt
@@ -26,7 +26,13 @@ coverage==4.5.4
 decorator==4.4.1
 deprecated==1.2.10
 dns-lexicon==3.3.17
-dnspython==1.15.0
+# There is no version of dnspython that works on both Python 2 and Python 3.9.
+# To work around this, we make use of the fact that subject to other
+# constraints, pip will install the newest version of a package while ignoring
+# versions that don't support the version of Python being used. The result of
+# this is dnspython 2.0.0 is installed in Python 3 while dnspython 1.16.0 is
+# installed in Python 2.
+dnspython<=2.0.0
 docker==4.3.1
 docker-compose==1.26.2
 docker-pycreds==0.4.0
diff --git a/tools/merge_requirements.py b/tools/merge_requirements.py
index 0d41d12c4..1f095c54e 100755
--- a/tools/merge_requirements.py
+++ b/tools/merge_requirements.py
@@ -1,8 +1,9 @@
 #!/usr/bin/env python
 """Merges multiple Python requirements files into one file.
 
-Requirements files specified later take precedence over earlier ones. Only
-simple SomeProject==1.2.3 format is currently supported.
+Requirements files specified later take precedence over earlier ones.
+Only the simple formats SomeProject==1.2.3 or SomeProject<=1.2.3 are
+currently supported.
 
 """
 from __future__ import print_function
@@ -16,17 +17,22 @@ def process_entries(entries):
 
     :param list entries: List of entries
 
-    :returns: mapping from a project to its pinned version
+    :returns: mapping from a project to its version specifier
     :rtype: dict
     """
     data = {}
     for e in entries:
         e = e.strip()
         if e and not e.startswith('#') and not e.startswith('-e'):
-            project, version = e.split('==')
-            if not version:
+            for comparison in ('==', '<=',):
+                parts = e.split(comparison)
+                if len(parts) == 2:
+                    project_name = parts[0]
+                    version = parts[1]
+                    data[project_name] = comparison + version
+                    break
+            else:
                 raise ValueError("Unexpected syntax '{0}'".format(e))
-            data[project] = version
     return data
 
 def read_file(file_path):
@@ -44,10 +50,11 @@ def read_file(file_path):
 def output_requirements(requirements):
     """Prepare print requirements to stdout.
 
-    :param dict requirements: mapping from a project to its pinned version
+    :param dict requirements: mapping from a project to its version
+        specifier
 
     """
-    return '\n'.join('{0}=={1}'.format(key, value)
+    return '\n'.join('{0}{1}'.format(key, value)
                      for key, value in sorted(requirements.items()))