Experiment for Python issue 15805: An attempt at adding redirect_stdin, redirect_stdout, and redirect_stderr context manager functions to the `io` module

io_module_redirect_stdin_stdout_stderr.patch

diff -r e7305517260b Lib/io.py
--- a/Lib/io.py                  Sat Jul 20 15:12:19 2013 +0200
+++ b/Lib/io.py	Sun Jul 21 10:14:26 2013 -0700
@@ -56,6 +56,8 @@
                  BufferedWriter, BufferedRWPair, BufferedRandom,
                  IncrementalNewlineDecoder, TextIOWrapper)
 
+from unittest.mock import patch
+
 OpenWrapper = _io.open # for compatibility with _pyio
 
 # Pretend this exception was created here.
@@ -90,3 +92,64 @@
 for klass in (StringIO, TextIOWrapper):
     TextIOBase.register(klass)
 del klass
+
+def redirect_stdin(replacement=None):
+    """Redirect stdin to come from a StringIO or str.
+
+    'replacement' is a StringIO or str.
+
+    Examples:
+
+    >>> from io import redirect_stdin, StringIO
+    >>> with redirect_stdin(StringIO("bleargh")) as s:
+    ...     x = input()
+    ...
+    >>> x
+    'bleargh'
+
+    >>> with redirect_stdin("bleargh") as s:
+    ...     x = input()
+    ...
+    >>> x
+    'bleargh'
+    """
+    if hasattr(replacement, 'readline'):  # a file-like object
+        file_like_obj = replacement
+    else:
+        # Try to convert to a file-like object; this works for strs at least
+        file_like_obj = StringIO(replacement)
+
+    return redirect_stdfile('sys.stdin', file_like_obj)
+
+def redirect_stdout(replacement=None):
+    """Redirect stdout to a StringIO.
+
+    Example:
+
+    >>> from io import redirect_stdout
+    >>> with redirect_stdout() as s:
+    ...     print('hello')
+    ...
+    >>> s.getvalue()
+    'hello\n'
+    """
+    return redirect_stdfile('sys.stdout', replacement)
+
+def redirect_stderr(replacement=None):
+    """Redirect stderr to a StringIO.
+
+    Example:
+
+    >>> import sys
+    >>> from io import redirect_stderr
+    >>> with redirect_stderr() as s:
+    ...     print("bleargh", file=sys.stderr)
+    ...
+    >>> s.getvalue()
+    'bleargh\n'
+    """
+    return redirect_stdfile('sys.stderr', replacement)
+
+def redirect_stdfile(stdfilename, replacement=None):
+    # stdfilename is one of ('sys.stdin', 'sys.stdout', 'sys.stderr')
+    return patch(stdfilename, replacement if replacement is not None else StringIO())

test_redirect_issue_15805.py

import sys
from io import redirect_stdin, redirect_stdout, redirect_stderr, StringIO
from tempfile import TemporaryFile


#----------------------------------------------------------------------------
# redirect_stdin with a StringIO as input
#----------------------------------------------------------------------------

with redirect_stdin(StringIO("bleargh")) as s:
    foo = input()

print("captured stdin: %s" % s.getvalue())


#----------------------------------------------------------------------------
# redirect_stdin with a str as input
#----------------------------------------------------------------------------

with redirect_stdin("some text") as s:
    foo = input()

print("captured stdin: %s" % s.getvalue())


#----------------------------------------------------------------------------
# redirect_stdin with a file as input
#----------------------------------------------------------------------------

with TemporaryFile(mode='r+') as f:
    f.write("one\ntwo\nthree\n")
    f.seek(0)

    lst = []

    with redirect_stdin(f):
        for i in range(0, 3):
            lst.append(input())

    print('lst = %r' % lst)
    # lst = ['one', 'two', 'three']


#----------------------------------------------------------------------------
# redirect_stdout captures stdout to a StringIO
#----------------------------------------------------------------------------

with redirect_stdout() as s:
    sys.stdout.write("hello")

print("captured stdout: %s" % s.getvalue())


#----------------------------------------------------------------------------
# redirect_stderr captures stderr to a StringIO
#----------------------------------------------------------------------------

with redirect_stderr() as s:
    sys.stderr.write("hello")

print("captured stderr: %s" % s.getvalue())


#----------------------------------------------------------------------------
# Using redirect_stdout and redirect_stdin together
# redirect_stdout suppresses the prompt from `input`
# redirect_stdin with a StringIO as input
#----------------------------------------------------------------------------

with redirect_stdout(), redirect_stdin(StringIO("bleargh")) as s:
    foo = input("Type something> ")

print("captured stdin: %s" % s.getvalue())

Example output:

marca@marca-mac:~/dev/hg-repos/cpython$ DYLD_FRAMEWORK_PATH=. \
> ./python.exe test_redirect_issue_15805.py
captured stdin: bleargh
captured stdin: some text
lst = ['one', 'two', 'three']
captured stdout: hello
captured stderr: hello
captured stdin: bleargh

marca@marca-mac:~/dev/hg-repos/cpython$ hg tip
changeset:   84735:e7305517260b
tag:         tip
parent:      84733:9d93a267b8a0
parent:      84734:76bb3fe6ce8f
user:        Christian Heimes <[email protected]>
date:        Sat Jul 20 15:12:19 2013 +0200
files:       Modules/_elementtree.c
description:
Add missing check of PyDict_Update()'s return value in _elementtree.c
CID 719637

http://bugs.python.org/issue15805

https://github.com/msabramo/redirectory