Write one error message directly to stderr instead of sys.stderr. This

lets us avoid taking the GIL, which might crash in case the Python
interpreter is not initialized at all.

1 files changed, 37 insertions, 0 deletions

diff --git a/testing/support.py b/testing/support.py
index 17c56cd..17ee621 100644
--- a/testing/support.py
+++ b/testing/support.py
@@ -17,3 +17,40 @@ else:
     u = ""
     unicode = str
     long = int
+
+
+class StdErrCapture(object):
+    """Capture writes to sys.stderr (not to the underlying file descriptor)."""
+    def __enter__(self):
+        import StringIO
+        self.old_stderr = sys.stderr
+        sys.stderr = f = StringIO.StringIO()
+        return f
+    def __exit__(self, *args):
+        sys.stderr = self.old_stderr
+
+
+class FdWriteCapture(object):
+    """xxx limited to capture at most 512 bytes of output, according
+    to the Posix manual."""
+
+    def __init__(self, capture_fd=2):    # stderr by default
+        self.capture_fd = capture_fd
+
+    def __enter__(self):
+        import os
+        self.read_fd, self.write_fd = os.pipe()
+        self.copy_fd = os.dup(self.capture_fd)
+        os.dup2(self.write_fd, self.capture_fd)
+        return self
+
+    def __exit__(self, *args):
+        import os
+        os.dup2(self.copy_fd, self.capture_fd)
+        os.close(self.copy_fd)
+        os.close(self.write_fd)
+        self._value = os.read(self.read_fd, 512)
+        os.close(self.read_fd)
+
+    def getvalue(self):
+        return self._value