support working directly with file descriptors

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 - Use pytest instead of parameterizedtestcase (PR [#657](https://github.com/RaRe-Technologies/smart_open/pull/657), [@mpenkov](https://github.com/mpenkov))
 - Support container client and blob client for azure blob storage (PR [#652](https://github.com/RaRe-Technologies/smart_open/pull/652), [@cbare](https://github.com/cbare))
+- Support working directly with file descriptors (PR [#659](https://github.com/RaRe-Technologies/smart_open/pull/659), [@mpenkov](https://github.com/mpenkov))
 - Fix AttributeError when reading passthrough zstandard (PR [#658](https://github.com/RaRe-Technologies/smart_open/pull/658), [@mpenkov](https://github.com/mpenkov))
 
 # 5.2.1, 28 August 2021

smart_open/compression.py

@@ -120,6 +120,7 @@ def compression_wrapper(file_obj, mode, compression):
     elif compression == INFER_FROM_EXTENSION:
         try:
             filename = file_obj.name
+            filename.upper()  # make sure this thing is a string
         except (AttributeError, TypeError):
             logger.warning(
                 'unable to transparently decompress %r because it '

smart_open/smart_open_lib.py

@@ -394,6 +394,17 @@ def _open_binary_stream(uri, mode, transport_params):
                 pass
         return uri
 
+    if isinstance(uri, int):
+        #
+        # We're working with a file descriptor.  If we open it, its name is
+        # just the integer value, which isn't helpful.  Unfortunately, there's
+        # no easy cross-platform way to go from a file descriptor to the filename,
+        # so we just give up here.  The user will have to handle their own
+        # compression, etc. explicitly.
+        #
+        fobj = _builtin_open(uri, mode, closefd=False)
+        return fobj
+
     if not isinstance(uri, str):
         raise TypeError("don't know how to handle uri %s" % repr(uri))
 

smart_open/tests/test_smart_open.py

@@ -2060,6 +2060,28 @@ def test_backwards_compatibility_wrapper():
         smart_open.smart_open(fpath, unsupported_keyword_param=123)
 
 
+@pytest.mark.skipif(os.name == "nt", reason="this test does not work on Windows")
+def test_read_file_descriptor():
+    with smart_open.open(__file__) as fin:
+        expected = fin.read()
+
+    fd = os.open(__file__, os.O_RDONLY)
+    with smart_open.open(fd) as fin:
+        actual = fin.read()
+
+    assert actual == expected
+
+
+@pytest.mark.skipif(os.name == "nt", reason="this test does not work on Windows")
+def test_write_file_descriptor():
+    with tempfile.NamedTemporaryFile() as tmp:
+        with smart_open.open(os.open(tmp.name, os.O_WRONLY), 'wt') as fout:
+            fout.write("hello world")
+
+        with smart_open.open(tmp.name, 'rt') as fin:
+            assert fin.read() == "hello world"
+
+
 if __name__ == '__main__':
     logging.basicConfig(format='%(asctime)s : %(levelname)s : %(message)s', level=logging.DEBUG)
     unittest.main()