Merge pull request matplotlib#20766 from sauerburger/fix-ps-linedash

Fix line dash offset format in PS output

Author: jklymak

lib/matplotlib/backends/backend_ps.py

@@ -329,7 +329,8 @@ def set_linedash(self, offset, seq, store=True):
             if np.array_equal(seq, oldseq) and oldo == offset:
                 return
 
-        self._pswriter.write(f"[{_nums_to_str(*seq)}] {offset:d} setdash\n"
+        self._pswriter.write(f"[{_nums_to_str(*seq)}]"
+                             f" {_nums_to_str(offset)} setdash\n"
                              if seq is not None and len(seq) else
                              "[] 0 setdash\n")
         if store:

lib/matplotlib/tests/test_backend_ps.py

@@ -222,3 +222,15 @@ def test_fonttype(fonttype):
     test = b'/FontType ' + bytes(f"{fonttype}", encoding='utf-8') + b' def'
 
     assert re.search(test, buf.getvalue(), re.MULTILINE)
+
+
+def test_linedash():
+    """Test that dashed lines do not break PS output"""
+    fig, ax = plt.subplots()
+
+    ax.plot([0, 1], linestyle="--")
+
+    buf = io.BytesIO()
+    fig.savefig(buf, format="ps")
+
+    assert buf.tell() > 0