Backport PR #4581.

Fixing nbconvert writing unicode characters to redirected stdout.

IPython/nbconvert/writers/stdout.py

@@ -13,6 +13,7 b' Contains Stdout writer'
 # Imports
 #-----------------------------------------------------------------------------
 
+from IPython.utils import io
 from .base import WriterBase
 
 #-----------------------------------------------------------------------------
@@ -31,4 +32,4 b' class StdoutWriter(WriterBase):'
         See base for more...
         """
 
-        print(output)
+        io.unicode_std_stream().write(output)

IPython/utils/io.py

@@ -14,10 +14,12 b' from __future__ import print_function'
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
+import codecs
 import os
 import sys
 import tempfile
 from StringIO import StringIO
+from .py3compat import PY3
 
 #-----------------------------------------------------------------------------
 # Code
@@ -285,4 +287,25 b' class capture_output(object):'
         sys.stdout = self.sys_stdout
         sys.stderr = self.sys_stderr
 
+def unicode_std_stream(stream='stdout'):
+    """Get a wrapper to write unicode to stdout/stderr as UTF-8.
 
+    This ignores environment variables and default encodings, to reliably write
+    unicode to stdout or stderr.
+
+    ::
+
+        unicode_std_stream().write(u'ł@e¶ŧ←')
+    """
+    assert stream in ('stdout', 'stderr')
+    stream  = getattr(sys, stream)
+    if PY3:
+        try:
+            stream_b = stream.buffer
+        except AttributeError:
+            # sys.stdout has been replaced - use it directly
+            return stream
+    else:
+        stream_b = stream
+
+    return codecs.getwriter('utf-8')(stream_b)

IPython/utils/tests/test_io.py

@@ -12,7 +12,9 b''
 # Imports
 #-----------------------------------------------------------------------------
 from __future__ import print_function
+from __future__ import absolute_import
 
+import io as stdlib_io
 import sys
 
 from StringIO import StringIO
@@ -21,8 +23,9 b' from subprocess import Popen, PIPE'
 import nose.tools as nt
 
 from IPython.testing.ipunittest import ParametricTestCase
-from IPython.utils.io import Tee, capture_output
-from IPython.utils.py3compat import doctest_refactor_print
+from IPython.testing.decorators import skipif
+from IPython.utils.io import Tee, capture_output, unicode_std_stream
+from IPython.utils.py3compat import doctest_refactor_print, PY3
 
 #-----------------------------------------------------------------------------
 # Tests
@@ -84,3 +87,34 b' def test_capture_output():'
     
     nt.assert_equal(io.stdout, 'hi, stdout\n')
     nt.assert_equal(io.stderr, 'hi, stderr\n')
+
+def test_UnicodeStdStream():
+    # Test wrapping a bytes-level stdout
+    if PY3:
+        stdoutb = stdlib_io.BytesIO()
+        stdout = stdlib_io.TextIOWrapper(stdoutb, encoding='ascii')
+    else:
+        stdout = stdoutb = stdlib_io.BytesIO()
+
+    orig_stdout = sys.stdout
+    sys.stdout = stdout
+    try:
+        sample = u"@łe¶ŧ←"
+        unicode_std_stream().write(sample)
+
+        output = stdoutb.getvalue().decode('utf-8')
+        nt.assert_equal(output, sample)
+        assert not stdout.closed
+    finally:
+        sys.stdout = orig_stdout
+
+@skipif(not PY3, "Not applicable on Python 2")
+def test_UnicodeStdStream_nowrap():
+    # If we replace stdout with a StringIO, it shouldn't get wrapped.
+    orig_stdout = sys.stdout
+    sys.stdout = StringIO()
+    try:
+        nt.assert_is(unicode_std_stream(), sys.stdout)
+        assert not sys.stdout.closed
+    finally:
+        sys.stdout = orig_stdout
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