add support for zst writing

smart_open/compression.py

@@ -106,8 +106,8 @@ def _handle_gzip(file_obj, mode):
 
 
 def _handle_zstd(file_obj, mode):
-    import zstandard as zstd
-    result = zstd.ZstdDecompressor().stream_reader(file_obj, closefd=True)
+    import zstandard  # type: ignore
+    result = zstandard.open(filename=file_obj, mode=mode)
     return result
 
 

smart_open/tests/test_compression.py

@@ -7,6 +7,7 @@
 #
 import gzip
 import io
+import tempfile
 
 import pytest
 import zstandard as zstd
@@ -42,3 +43,15 @@ def label(thing, name):
 def test_compression_wrapper_read(fileobj, compression, filename):
     wrapped = smart_open.compression.compression_wrapper(fileobj, 'rb', compression, filename)
     assert wrapped.read() == plain
+
+
+def test_zst_write():
+    with tempfile.NamedTemporaryFile(suffix=".zst") as tmp:
+        with smart_open.open(tmp.name, "wt") as fout:
+            print("hello world", file=fout)
+            print("this is a test", file=fout)
+
+        with smart_open.open(tmp.name, "rt") as fin:
+            got = list(fin)
+
+    assert got == ["hello world\n", "this is a test\n"]