Fix python dependency hash equality

eql? should not depend on the hash value as hash values of uneql objects
can collide, but eql values may only collide for objects that are
actually eql.

Further, python dependencies are uniquely identified by the combination
of the name and imports attributes, so there is no reason to involved
the expensive binary computation for simple equality checks.

Fixes Homebrew/homebrew#20840.

Library/Homebrew/requirements/python_dependency.rb

@@ -16,6 +16,7 @@ require 'requirement'
 class PythonInstalled < Requirement
   attr_reader :min_version
   attr_reader :if3then3
+  attr_reader :imports
   attr_accessor :site_packages
   attr_accessor :binary # The python.rb formula needs to set the binary
 
@@ -342,15 +343,14 @@ class PythonInstalled < Requirement
     binary.to_s
   end
 
+  # Objects of this class are used to represent dependencies on Python and
+  # dependencies on Python modules, so the combination of name + imports is
+  # enough to identify them uniquely.
   def eql?(other)
-    instance_of?(other.class) && hash == other.hash
+    instance_of?(other.class) && name == other.name && imports == other.imports
   end
 
   def hash
-    # Requirements are a ComparableSet. So we define our identity by the
-    # selected python binary plus the @imports in order to support multiple:
-    #    depends_on :python => 'module1'
-    #    depends_on :python => 'module2'
-    (binary.to_s+@imports.to_s).hash
+    [name, *imports].hash
   end
 end