add version comparison utility

    
all version strings are comparable by casting string elements to float('inf')

IPython/utils/version.py

@@ -0,0 +1,56 b''
+# encoding: utf-8
+"""
+Utilities for version comparison
+
+It is a bit ridiculous that we need these.
+"""
+
+#-----------------------------------------------------------------------------
+#  Copyright (C) 2013  The IPython Development Team
+#
+#  Distributed under the terms of the BSD License.  The full license is in
+#  the file COPYING, distributed as part of this software.
+#-----------------------------------------------------------------------------
+
+#-----------------------------------------------------------------------------
+# Imports
+#-----------------------------------------------------------------------------
+
+from distutils.version import LooseVersion
+
+#-----------------------------------------------------------------------------
+# Code
+#-----------------------------------------------------------------------------
+
+class NumericalVersion(LooseVersion):
+    """A version of LooseVersion that is *always* comparable
+    
+    String elements (of any kind!) are interpreted as infinite.
+    Since these are generally only on development branches,
+    that is fairly safe, even though technically 1.0a1 should be less than 1.0.
+    """
+    def parse (self, vstring):
+        # I've given up on thinking I can reconstruct the version string
+        # from the parsed tuple -- so I just store the string here for
+        # use by __str__
+        self.vstring = vstring
+        components = filter(lambda x: x and x != '.',
+                            self.component_re.split(vstring))
+        for i in range(len(components)):
+            try:
+                components[i] = int(components[i])
+            except ValueError:
+                # this is the only change
+                components[i] = float('inf')
+
+        self.version = components
+
+def version_tuple(vs):
+    """Return a tuple of numbers from a version string.
+    
+    'dev' 'a', 'etc' are transformed to float('inf'),
+    so they will always compare positively to any
+    regular integer element.
+    """
+    return tuple(NumericalVersion(vs).version)
+    
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