is_fraction and make_fraction: convenience functions to handle transparently

the conditional availability of the fractions module in the standard library (Python ≥ 2.6).

3 files changed, 71 insertions, 2 deletions

diff --git a/src/pyexiv2/utils.py b/src/pyexiv2/utils.py
index 5b0a3d5..3c5aa95 100644
--- a/src/pyexiv2/utils.py
+++ b/src/pyexiv2/utils.py
@@ -250,6 +250,34 @@ class Rational(object):
         return '%d/%d' % (self._numerator, self._denominator)
 
 
+def is_fraction(obj):
+    """
+    Test whether the object is a valid fraction.
+    """
+    if Fraction is not None and isinstance(obj, Fraction):
+        return True
+    elif isinstance(obj, Rational):
+        return True
+    else:
+        return False
+
+
+def make_fraction(*args):
+    """
+    Make a fraction.
+
+    The type of the returned object depends on the availability of the
+    fractions module in the standard library (Python ≥ 2.6).
+    """
+    if Fraction is not None:
+        return Fraction(*args)
+    else:
+        if len(args) == 1:
+            return Rational.from_string(*args)
+        else:
+            return Rational(*args)
+
+
 class ListenerInterface(object):
 
     """
diff --git a/test/TestsRunner.py b/test/TestsRunner.py
index 198bb27..ba5162c 100755
--- a/test/TestsRunner.py
+++ b/test/TestsRunner.py
@@ -38,7 +38,7 @@ from xmp import TestXmpTag, TestXmpNamespaces
 from metadata import TestImageMetadata
 from buffer import TestBuffer
 from encoding import TestEncodings
-from utils import TestConversions
+from utils import TestConversions, TestFractions
 from usercomment import TestUserCommentReadWrite, TestUserCommentAdd
 from pickling import TestPicklingTags
 
@@ -58,6 +58,7 @@ def run_unit_tests():
     suite.addTest(unittest.defaultTestLoader.loadTestsFromTestCase(TestBuffer))
     suite.addTest(unittest.defaultTestLoader.loadTestsFromTestCase(TestEncodings))
     suite.addTest(unittest.defaultTestLoader.loadTestsFromTestCase(TestConversions))
+    suite.addTest(unittest.defaultTestLoader.loadTestsFromTestCase(TestFractions))
     suite.addTest(unittest.defaultTestLoader.loadTestsFromTestCase(TestUserCommentReadWrite))
     suite.addTest(unittest.defaultTestLoader.loadTestsFromTestCase(TestUserCommentAdd))
     suite.addTest(unittest.defaultTestLoader.loadTestsFromTestCase(TestPicklingTags))
diff --git a/test/utils.py b/test/utils.py
index 2f0d19b..ceddcc3 100644
--- a/test/utils.py
+++ b/test/utils.py
@@ -26,7 +26,8 @@
 
 import unittest
 
-from pyexiv2.utils import undefined_to_string, string_to_undefined
+from pyexiv2.utils import undefined_to_string, string_to_undefined, \
+                          Rational, Fraction, is_fraction, make_fraction
 
 
 class TestConversions(unittest.TestCase):
@@ -48,3 +49,42 @@ class TestConversions(unittest.TestCase):
         value = "48 50 50 49"
         self.assertEqual(string_to_undefined(undefined_to_string(value)), value)
 
+
+class TestFractions(unittest.TestCase):
+
+    def test_is_fraction(self):
+        if Fraction is not None:
+            self.failUnless(is_fraction(Fraction()))
+            self.failUnless(is_fraction(Fraction(3, 5)))
+            self.failUnless(is_fraction(Fraction(Fraction(4, 5))))
+            self.failUnless(is_fraction(Fraction('3/2')))
+            self.failUnless(is_fraction(Fraction('-4/5')))
+        self.failUnless(is_fraction(Rational(3, 5)))
+        self.failUnless(is_fraction(Rational(-4, 5)))
+        self.failUnless(is_fraction(Rational.from_string("3/5")))
+        self.failUnless(is_fraction(Rational.from_string("-4/5")))
+
+        self.failIf(is_fraction(3 / 5))
+        self.failIf(is_fraction('3/5'))
+        self.failIf(is_fraction('2.7'))
+        self.failIf(is_fraction(2.7))
+        self.failIf(is_fraction('notafraction'))
+        self.failIf(is_fraction(None))
+
+    def test_make_fraction(self):
+        if Fraction is not None:
+            self.assertEqual(make_fraction(3, 5), Fraction(3, 5))
+            self.assertEqual(make_fraction(-3, 5), Fraction(-3, 5))
+            self.assertEqual(make_fraction('3/2'), Fraction(3, 2))
+            self.assertEqual(make_fraction('-3/4'), Fraction(-3, 4))
+        else:
+            self.assertEqual(make_fraction(3, 5), Rational(3, 5))
+            self.assertEqual(make_fraction(-3, 5), Rational(-3, 5))
+            self.assertEqual(make_fraction('3/2'), Rational(3, 2))
+            self.assertEqual(make_fraction('-3/4'), Rational(-3, 4))
+
+        self.assertRaises(ZeroDivisionError, make_fraction, 3, 0)
+        self.assertRaises(ZeroDivisionError, make_fraction, '3/0')
+        self.assertRaises(TypeError, make_fraction, 5, 3, 2)
+        self.assertRaises(TypeError, make_fraction, None)
+