History expects single output per cell, and doesn't use JSON to store them in the database.

IPython/core/displayhook.py

@@ -283,8 +283,8 b' class DisplayHook(Configurable):'
         if self.shell.logger.log_output:
             self.shell.logger.log_write(format_dict['text/plain'], 'output')
         # This is a defaultdict of lists, so we can always append
-        self.shell.history_manager.output_hist_reprs[self.prompt_count]\
-                                    .append(format_dict['text/plain'])
+        self.shell.history_manager.output_hist_reprs[self.prompt_count] = \
+                                                    format_dict['text/plain']
 
     def finish_displayhook(self):
         """Finish up all displayhook activities."""

IPython/core/history.py

@@ -15,14 +15,11 b' from __future__ import print_function'
 # Stdlib imports
 import atexit
 import datetime
-import json
 import os
 import re
 import sqlite3
 import threading
 
-from collections import defaultdict
-
 # Our own packages
 from IPython.config.configurable import Configurable
 import IPython.utils.io
@@ -56,11 +53,10 b' class HistoryManager(Configurable):'
             return []
 
     # A dict of output history, keyed with ints from the shell's
-    # execution count. If there are several outputs from one command,
-    # only the last one is stored.
+    # execution count.
     output_hist = Dict()
-    # Contains all outputs, in lists of reprs.
-    output_hist_reprs = Instance(defaultdict, args=(list,))
+    # The text/plain repr of outputs.
+    output_hist_reprs = Dict()
 
     # String holding the path to the history file
     hist_file = Unicode(config=True)
@@ -218,9 +214,7 b' class HistoryManager(Configurable):'
         cur = self.db.execute("SELECT session, line, %s FROM %s " %\
                                 (toget, sqlfrom) + sql, params)
         if output:    # Regroup into 3-tuples, and parse JSON
-            loads = lambda out: json.loads(out) if out else None
-            return ((ses, lin, (inp, loads(out))) \
-                                        for ses, lin, inp, out in cur)
+            return ((ses, lin, (inp, out)) for ses, lin, inp, out in cur)
         return cur
         
     
@@ -419,9 +413,9 b' class HistoryManager(Configurable):'
         line_num : int
           The line number from which to save outputs
         """
-        if (not self.db_log_output) or not self.output_hist_reprs[line_num]:
+        if (not self.db_log_output) or (line_num not in self.output_hist_reprs):
             return
-        output = json.dumps(self.output_hist_reprs[line_num])
+        output = self.output_hist_reprs[line_num]
         
         with self.db_output_cache_lock:
             self.db_output_cache.append((line_num, output))
@@ -696,7 +690,7 b" def magic_history(self, parameter_s = ''):"
                 inline = "\n... ".join(inline.splitlines()) + "\n..."
         print(inline, file=outfile)
         if get_output and output:
-            print("\n".join(output), file=outfile)
+            print(output, file=outfile)
 
     if close_at_end:
         outfile.close()

IPython/core/tests/test_history.py

@@ -33,7 +33,7 b' def test_history():'
             
             ip.history_manager.db_log_output = True
             # Doesn't match the input, but we'll just check it's stored.
-            ip.history_manager.output_hist_reprs[3].append("spam")
+            ip.history_manager.output_hist_reprs[3] = "spam"
             ip.history_manager.store_output(3)
             
             nt.assert_equal(ip.history_manager.input_hist_raw, [''] + hist)
@@ -53,7 +53,7 b' def test_history():'
             # Check get_hist_tail
             gothist = ip.history_manager.get_tail(4, output=True,
                                                     include_latest=True)
-            expected = [(1, 3, (hist[-1], ["spam"])),
+            expected = [(1, 3, (hist[-1], "spam")),
                         (2, 1, (newcmds[0], None)),
                         (2, 2, (newcmds[1], None)),
                         (2, 3, (newcmds[2], None)),]
@@ -68,7 +68,7 b' def test_history():'
             gothist = ip.history_manager.search("*test*")
             nt.assert_equal(list(gothist), [(1,2,hist[1])] )
             gothist = ip.history_manager.search("b*", output=True)
-            nt.assert_equal(list(gothist), [(1,3,(hist[2],["spam"]))] )
+            nt.assert_equal(list(gothist), [(1,3,(hist[2],"spam"))] )
             
             # Cross testing: check that magic %save can get previous session.
             testfilename = os.path.realpath(os.path.join(tmpdir, "test.py"))