Index: Lib/csv.py
===================================================================
--- Lib/csv.py	(revision 62313)
+++ Lib/csv.py	(working copy)
@@ -233,10 +233,12 @@
                            (delims[a] > delims[b]) and a or b, delims.keys())
             skipinitialspace = delims[delim] == spaces
             if delim == '\n': # most likely a file with a single column
-                delim = ''
+                # comma is as good as any other delimiter in this case
+                delim = ','
         else:
             # there is *no* delimiter, it's a single column of quoted data
-            delim = ''
+            # comma is as good as any other delimiter in this case
+            delim = ','
             skipinitialspace = 0
 
         return (quotechar, delim, skipinitialspace)
@@ -317,8 +319,12 @@
 
             if len(delims) == 1:
                 delim = delims.keys()[0]
-                skipinitialspace = (data[0].count(delim) ==
-                                    data[0].count("%c " % delim))
+                if delim.isdigit() or delim.isalpha():
+                    delim = ","
+                    skipinitialspace = False
+                else:
+                    skipinitialspace = (data[0].count(delim) ==
+                                        data[0].count("%c " % delim))
                 return (delim, skipinitialspace)
 
             # analyze another chunkLength lines
@@ -331,19 +337,25 @@
         # if there's more than one, fall back to a 'preferred' list
         if len(delims) > 1:
             for d in self.preferred:
-                if d in delims.keys():
+                if d in delims:
                     skipinitialspace = (data[0].count(d) ==
                                         data[0].count("%c " % d))
                     return (d, skipinitialspace)
 
         # nothing else indicates a preference, pick the character that
         # dominates(?)
-        items = [(v,k) for (k,v) in delims.items()]
-        items.sort()
-        delim = items[-1][1]
+        items = [(v,k) for (k,v) in delims.items()
+                     if not (k.isalpha() or k.isdigit())]
+        if not items:
+            # go with the favorite
+            delim = ','
+            skipinitialspace = 0
+        else:
+            items.sort()
+            delim = items[-1][1]
+            skipinitialspace = (data[0].count(delim) ==
+                                data[0].count("%c " % delim))
 
-        skipinitialspace = (data[0].count(delim) ==
-                            data[0].count("%c " % delim))
         return (delim, skipinitialspace)
 
 
Index: Lib/test/test_csv.py
===================================================================
--- Lib/test/test_csv.py	(revision 62313)
+++ Lib/test/test_csv.py	(working copy)
@@ -861,6 +861,27 @@
     sample6 = "a|b|c\r\nd|e|f\r\n"
     sample7 = "'a'|'b'|'c'\r\n'd'|e|f\r\n"
 
+    sample8 = """\
+43.4e12
+147483648
+47483648
+"""
+    sample9 = """\
+abcdef
+bcdefg
+cdefgh
+"""
+
+    sample10 = '''\
+"Sequence"
+"AALENTHLL"
+"RQILNADAM"
+"GALENAKAEI"
+"NSPANNIVM"
+"AQIRNLTVL"
+"AGPENSSKI"
+'''
+
     def test_has_header(self):
         sniffer = csv.Sniffer()
         self.assertEqual(sniffer.has_header(self.sample1), False)
@@ -899,8 +920,23 @@
         self.assertEqual(dialect.delimiter, "|")
         self.assertEqual(dialect.quotechar, "'")
 
+    def test_one_column(self):
+        sniffer = csv.Sniffer()
+        # Not much to go on in sample8 or sample9.  We hope for useful
+        # defaults.
+        dialect = sniffer.sniff(self.sample8)
+        self.assertEqual(dialect.delimiter, ',')
+        self.assertEqual(dialect.quotechar, '"')
+        dialect = sniffer.sniff(self.sample9)
+        self.assertEqual(dialect.delimiter, ',')
+        self.assertEqual(dialect.quotechar, '"')
+        dialect = sniffer.sniff(self.sample10)
+        self.assertEqual(dialect.delimiter, ',')
+        self.assertEqual(dialect.quotechar, '"')
+
 if not hasattr(sys, "gettotalrefcount"):
-    if test_support.verbose: print "*** skipping leakage tests ***"
+    if test_support.verbose:
+        print "*** skipping leakage tests ***"
 else:
     class NUL:
         def write(s, *args):