diff -r 5e12ad3013ff Lib/test/test_csv.py
--- a/Lib/test/test_csv.py	Mon Aug 27 19:50:36 2012 +0100
+++ b/Lib/test/test_csv.py	Fri Aug 31 19:53:02 2012 +0200
@@ -207,7 +207,6 @@
             fileobj.close()
             os.unlink(name)
 
-    @unittest.skipIf(test_support.is_jython, "FIXME: not working in Jython")
     def test_write_float(self):
         # Issue 13573: loss of precision because csv.writer
         # uses str() for floats instead of repr()
@@ -603,10 +602,9 @@
     ### "long" means the row is longer than the number of fieldnames
     ### "short" means there are fewer elements in the row than fieldnames
 
-    @unittest.skipIf(test_support.is_jython, "FIXME: not working in Jython")
     def test_write_simple_dict(self):
         fd, name = tempfile.mkstemp()
-        fileobj = io.open(fd, 'w+b')
+        fileobj = os.fdopen(fd, 'w+b')
         try:
             writer = csv.DictWriter(fileobj, fieldnames = ["f1", "f2", "f3"])
             writer.writeheader()
@@ -790,7 +788,6 @@
             fileobj.close()
             os.unlink(name)
 
-    @unittest.skipIf(test_support.is_jython, "FIXME: not working in Jython")
     def test_double_write(self):
         import array
         contents = [(20-i)*0.1 for i in range(20)]
@@ -807,7 +804,6 @@
             fileobj.close()
             os.unlink(name)
 
-    @unittest.skipIf(test_support.is_jython, "FIXME: not working in Jython")
     def test_float_write(self):
         import array
         contents = [(20-i)*0.1 for i in range(20)]
diff -r 5e12ad3013ff src/org/python/modules/_csv/PyWriter.java
--- a/src/org/python/modules/_csv/PyWriter.java	Mon Aug 27 19:50:36 2012 +0100
+++ b/src/org/python/modules/_csv/PyWriter.java	Fri Aug 31 19:53:02 2012 +0200
@@ -1,8 +1,11 @@
 /* Copyright (c) Jython Developers */
 package org.python.modules._csv;
 
+import java.util.ArrayList;
+
 import org.python.core.Py;
 import org.python.core.PyException;
+import org.python.core.PyFloat;
 import org.python.core.PyObject;
 import org.python.core.PyString;
 import org.python.core.PyType;
@@ -38,6 +41,13 @@
 
     /** Whether field should be quoted during a join. */
     private boolean quoted = false;
+    
+    /** The list of classes that must use __repr__ for serialization */
+    private ArrayList<Class<? extends PyObject>> reprTypes = new ArrayList<Class<? extends PyObject>>();
+    {
+    	// instance initializer
+    	reprTypes.add(PyFloat.class);
+    }
 
     public PyWriter(PyObject writeline, PyDialect dialect) {
         this.writeline = writeline;
@@ -130,7 +140,13 @@
             } else if (field == Py.None) {
                 append_ok = join_append("", len == 1);
             } else {
-                PyObject str = field.__str__();
+            	
+                PyObject str;
+                if (reprTypes.contains(field.getClass()))
+                	str = field.__repr__();
+                else
+                	str = field.__str__();
+                
                 if (str == null) {
                     return false;
                 }