Disable IPython History in executing preprocessor

nbconvert/preprocessors/execute.py

@@ -220,6 +220,20 @@ class ExecutePreprocessor(Preprocessor):
             )
     ).tag(config=True)
 
+    ipython_hist_file = Unicode(
+        default_value=':memory:',
+        help="""Path to file to use for SQLite history database for an IPython kernel.
+
+        The specific value `:memory:` (including the colon
+        at both end but not the back ticks), avoids creating a history file. Otherwise, IPython
+        will create a history file for each kernel. 
+
+        When running kernels simultaneously (e.g. via multiprocessing) saving history a single
+        SQLite file can result in database errors, so using `:memory:` is recommended in non-interactive
+        contexts.
+
+        """).tag(config=True)
+
     kernel_manager_class = Type(
         config=True,
         help='The kernel manager class to use.'
@@ -268,6 +282,8 @@ def start_new_kernel(self, **kwargs):
                 'kernelspec', {}).get('name', 'python')
         km = self.kernel_manager_class(kernel_name=self.kernel_name,
                                        config=self.config)
+        if km.ipykernel and self.ipython_hist_file:
+            self.extra_arguments += ['--HistoryManager.hist_file={}'.format(self.ipython_hist_file)]
         km.start_kernel(extra_arguments=self.extra_arguments, **kwargs)
 
         kc = km.client()

nbconvert/preprocessors/tests/files/Check History in Memory.ipynb

@@ -0,0 +1,28 @@
+{
+ "cells": [
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "from IPython import get_ipython"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "metadata": {
+    "scrolled": true
+   },
+   "outputs": [],
+   "source": [
+    "ip = get_ipython()\n",
+    "assert ip.history_manager.hist_file == ':memory:'"
+   ]
+  }
+ ],
+ "metadata": {},
+ "nbformat": 4,
+ "nbformat_minor": 2
+}

nbconvert/preprocessors/tests/files/Parallel Execute.ipynb

@@ -0,0 +1,65 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Ensure notebooks can execute in parallel\n",
+    "\n",
+    "This notebook uses a file system based \"lock\" to assert that two instances of the notebook kernel will run in parallel. Each instance writes to a file in a temporary directory, and then tries to read the other file from\n",
+    "the temporary directory, so that running them in sequence will fail, but running them in parallel will succed.\n",
+    "\n",
+    "Two notebooks are launched, each with an injected cell which sets the `this_notebook` variable. One notebook is set to `this_notebook = 'A'` and the other `this_notebook = 'B'`."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "import os\n",
+    "import os.path\n",
+    "import tempfile\n",
+    "import time"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "# the variable this_notebook is injectected in a cell above by the test framework.\n",
+    "other_notebook = {'A':'B', 'B':'A'}[this_notebook]\n",
+    "directory = os.environ['NBEXECUTE_TEST_PARALLEL_TMPDIR']\n",
+    "with open(os.path.join(directory, 'test_file_{}.txt'.format(this_notebook)), 'w') as f:\n",
+    "    f.write('Hello from {}'.format(this_notebook))"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "start = time.time()\n",
+    "timeout = 5\n",
+    "end = start + timeout\n",
+    "target_file = os.path.join(directory, 'test_file_{}.txt'.format(other_notebook))\n",
+    "while time.time() < end:\n",
+    "    time.sleep(0.1)\n",
+    "    if os.path.exists(target_file):\n",
+    "        with open(target_file, 'r') as f:\n",
+    "            text = f.read()\n",
+    "        if text == 'Hello from {}'.format(other_notebook):\n",
+    "            break\n",
+    "else:\n",
+    "    assert False, \"Timed out – didn't get a message from {}\".format(other_notebook)"
+   ]
+  }
+ ],
+ "metadata": {},
+ "nbformat": 4,
+ "nbformat_minor": 2
+}

nbconvert/preprocessors/tests/test_execute.py

@@ -13,6 +13,8 @@
 import io
 import os
 import re
+import threading
+import multiprocessing as mp
 
 import nbformat
 import sys
@@ -69,14 +71,17 @@ def build_preprocessor(opts):
     return preprocessor
 
 
-def run_notebook(filename, opts, resources):
+def run_notebook(filename, opts, resources, preprocess_notebook=None):
     """Loads and runs a notebook, returning both the version prior to
     running it and the version after running it.
 
     """
     with io.open(filename) as f:
         input_nb = nbformat.read(f, 4)
 
+    if preprocess_notebook:
+        input_nb = preprocess_notebook(input_nb)
+
     preprocessor = build_preprocessor(opts)
     cleaned_input_nb = copy.deepcopy(input_nb)
     for cell in cleaned_input_nb.cells:
@@ -218,6 +223,13 @@ def assert_notebooks_equal(expected, actual):
         actual_execution_count = actual_cell.get('execution_count', None)
         assert expected_execution_count == actual_execution_count
 
+def notebook_resources():
+    """Prepare a notebook resources dictionary for executing test notebooks in the `files` folder."""
+    res = ResourcesDict()
+    res['metadata'] = ResourcesDict()
+    res['metadata']['path'] = os.path.join(current_dir, 'files')
+    return res
+
 
 @pytest.mark.parametrize(
     ["input_name", "opts"],
@@ -238,18 +250,66 @@ def assert_notebooks_equal(expected, actual):
         ("Unicode.ipynb", dict(kernel_name="python")),
         ("UnicodePy3.ipynb", dict(kernel_name="python")),
         ("update-display-id.ipynb", dict(kernel_name="python")),
+        ("Check History in Memory.ipynb", dict(kernel_name="python")),
     ]
 )
 def test_run_all_notebooks(input_name, opts):
     """Runs a series of test notebooks and compares them to their actual output"""
     input_file = os.path.join(current_dir, 'files', input_name)
-    res = ResourcesDict()
-    res['metadata'] = ResourcesDict()
-    res['metadata']['path'] = os.path.join(current_dir, 'files')
-    input_nb, output_nb = run_notebook(input_file, opts, res)
+    input_nb, output_nb = run_notebook(input_file, opts, notebook_resources())
     assert_notebooks_equal(input_nb, output_nb)
 
 
+def label_parallel_notebook(nb, label):
+    """Insert a cell in a notebook which sets the variable `this_notebook` to the string `label`.
+
+    Used for parallel testing to label two notebooks which are run simultaneously.
+    """
+    label_cell = nbformat.NotebookNode(
+        {
+            "cell_type": "code",
+            "execution_count": None,
+            "metadata": {},
+            "outputs": [],
+            "source": "this_notebook = '{}'".format(label),
+        }
+    )
+
+    nb.cells.insert(1, label_cell)
+    return nb
+
+
+def test_parallel_notebooks(capfd, tmpdir):
+    """Two notebooks should be able to be run simultaneously without problems.
+
+    The two notebooks spawned here use the filesystem to check that the other notebook
+    wrote to the filesystem."""
+
+    opts = dict(kernel_name="python")
+    input_name = "Parallel Execute.ipynb"
+    input_file = os.path.join(current_dir, "files", input_name)
+    res = notebook_resources()
+
+    with modified_env({"NBEXECUTE_TEST_PARALLEL_TMPDIR": str(tmpdir)}):
+        threads = [
+            threading.Thread(
+                target=run_notebook,
+                args=(
+                    input_file,
+                    opts,
+                    res,
+                    functools.partial(label_parallel_notebook, label=label),
+                ),
+            )
+            for label in ("A", "B")
+        ]
+        [t.start() for t in threads]
+        [t.join(timeout=2) for t in threads]
+
+    captured = capfd.readouterr()
+    assert captured.err == ""
+
+
 class TestExecute(PreprocessorTestsBase):
     """Contains test functions for execute.py"""
     maxDiff = None