discard stdout and stderr from Jupyter kernel processes (#53)

CHANGELOG.md

@@ -47,6 +47,11 @@
 * Fixed an encoding bug that prevented `svg` rich output from being displayed.
   Added `svg` to the collection of rich output formats that are automatically displayed (#53).
 
+* stdout and stderr from Jupyter kernel processes are no longer included in
+  Codebraid's stdout and stderr.  Some kernels such as IJulia write messages
+  to output streams during startup.  This was causing error messages in
+  Codebraid Preview and incorrect documents when Codebraid outputs to stdout.
+
 * Fixed a bug that prevented Jupyter kernels from being used when the kernel
   name, kernel display name, and kernel language were not all different from
   each other.

codebraid/codeprocessors/exec_jupyter.py

@@ -13,10 +13,11 @@
 
 import base64
 import collections
+import pathlib
 import queue
 import re
+import subprocess
 import time
-import pathlib
 try:
     import jupyter_client
 except ImportError:
@@ -119,7 +120,7 @@ async def exec(session: Session, *, cache_key_path: pathlib.Path, progress: Prog
 
     kernel_manager = jupyter_client.AsyncKernelManager(kernel_name=kernel_name)
     try:
-        await kernel_manager.start_kernel()
+        await kernel_manager.start_kernel(stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)
     except jupyter_client.kernelspec.NoSuchKernel:
         msg = f'No Jupyter kernel was found for "{session.jupyter_kernel}"'
         session.errors.append(message.SysConfigError(msg))

codebraid/version.py

@@ -1,4 +1,4 @@
 # -*- coding: utf-8 -*-
 
 from .fmtversion import get_version_plus_info
-__version__, __version_info__ = get_version_plus_info(0, 10, 0, 'dev', 5)
+__version__, __version_info__ = get_version_plus_info(0, 10, 0, 'dev', 6)