Added support for os.pipe

- see pytest-dev#473

CHANGES.md

@@ -3,6 +3,9 @@ The release versions are PyPi releases.
 
 ## Version 3.6 (as yet unreleased)
 
+#### New Features
+  * added support for `os.pipe` (see [#473](../../issues/473))
+
 ## [Version 3.5.8](https://pypi.python.org/pypi/pyfakefs/3.5.8)
 
 Another bug-fix release that mainly fixes a regression wih Python 2 that has 

pyfakefs/fake_filesystem.py

@@ -3738,13 +3738,27 @@ def write(self, file_des, contents):
         file_handle = self.filesystem.get_open_file(file_des)
         if isinstance(file_handle, FakeDirWrapper):
             self.filesystem.raise_os_error(errno.EBADF, file_handle.file_path)
+
+        if isinstance(file_handle, FakePipeWrapper):
+            return file_handle.write(contents)
+
         file_handle.raw_io = True
         file_handle._sync_io()
         file_handle.update_flush_pos()
         file_handle.write(contents)
         file_handle.flush()
         return len(contents)
 
+    def pipe(self):
+        read_fd, write_fd = os.pipe()
+        read_wrapper = FakePipeWrapper(self.filesystem, read_fd)
+        file_des = self.filesystem._add_open_file(read_wrapper)
+        read_wrapper.filedes = file_des
+        write_wrapper = FakePipeWrapper(self.filesystem, write_fd)
+        file_des = self.filesystem._add_open_file(write_wrapper)
+        write_wrapper.filedes = file_des
+        return read_wrapper.filedes, write_wrapper.filedes
+
     @staticmethod
     def stat_float_times(newvalue=None):
         """Determine whether a file's time stamps are reported as floats
@@ -5019,6 +5033,37 @@ def close(self):
         self._filesystem._close_open_file(self.filedes)
 
 
+class FakePipeWrapper(object):
+    """Wrapper for a read or write descriptor of a real pipe object to be
+    used in open files list.
+    """
+
+    def __init__(self, filesystem, fd):
+        self._filesystem = filesystem
+        self.fd = fd  # the real file descriptor
+        self.filedes = None
+
+    def get_object(self):
+        return None
+
+    def fileno(self):
+        """Return the fake file descriptor of the pipe object."""
+        return self.filedes
+
+    def read(self, numBytes):
+        """Read from the real pipe."""
+        return os.read(self.fd, numBytes)
+
+    def write(self, contents):
+        """Write to the real pipe."""
+        return os.write(self.fd, contents)
+
+    def close(self):
+        """Close the pipe descriptor."""
+        self._filesystem.open_files[self.filedes].remove(self)
+        os.close(self.fd)
+
+
 Deprecator.add(FakeFileWrapper, FakeFileWrapper.get_object, 'GetObject')
 Deprecator.add(FakeFileWrapper, FakeFileWrapper.size, 'Size')
 

pyfakefs/tests/fake_os_test.py

@@ -2649,6 +2649,42 @@ def test_open_umask_applied(self):
         self.open(file2, 'w').close()
         self.assert_mode_equal(0o640, self.os.stat(file2).st_mode)
 
+    def test_open_pipe(self):
+        read_fd, write_fd = self.os.pipe()
+        self.os.close(read_fd)
+        self.os.close(write_fd)
+
+    def test_open_pipe_with_existing_fd(self):
+        file1 = self.make_path('file1')
+        fd = self.os.open(file1, os.O_CREAT)
+        read_fd, write_fd = self.os.pipe()
+        self.assertGreater(read_fd, fd)
+        self.os.close(fd)
+        self.os.close(read_fd)
+        self.os.close(write_fd)
+
+    def test_open_file_with_existing_pipe(self):
+        read_fd, write_fd = self.os.pipe()
+        file1 = self.make_path('file1')
+        fd = self.os.open(file1, os.O_CREAT)
+        self.assertGreater(fd, write_fd)
+        self.os.close(read_fd)
+        self.os.close(write_fd)
+        self.os.close(fd)
+
+    def test_write_to_pipe(self):
+        read_fd, write_fd = self.os.pipe()
+        self.os.write(write_fd, b'test')
+        self.assertEqual(b'test', self.os.read(read_fd, 4))
+        self.os.close(read_fd)
+        self.os.close(write_fd)
+
+    def test_write_to_read_fd(self):
+        read_fd, write_fd = self.os.pipe()
+        self.assert_raises_os_error(errno.EBADF,
+                                    self.os.write, read_fd, b'test')
+        self.os.close(read_fd)
+        self.os.close(write_fd)
 
 class RealOsModuleTest(FakeOsModuleTest):
     def use_real_fs(self):