diff -r e8f3740cc067 -r 94f3a73b6672 rust/hg-cpython/src/exceptions.rs
--- a/rust/hg-cpython/src/exceptions.rs	Wed Apr 24 11:34:09 2019 +0200
+++ b/rust/hg-cpython/src/exceptions.rs	Fri May 17 09:36:29 2019 -0400
@@ -12,8 +12,8 @@
 //! existing Python exceptions if appropriate.
 //!
 //! [`GraphError`]: struct.GraphError.html
-use cpython::exc::ValueError;
-use cpython::{PyErr, Python};
+use cpython::exc::{ValueError, RuntimeError};
+use cpython::{PyErr, Python, exc};
 use hg;
 
 py_exception!(rustext, GraphError, ValueError);
@@ -28,9 +28,43 @@
                 match py
                     .import("mercurial.error")
                     .and_then(|m| m.get(py, "WdirUnsupported"))
-                {
-                    Err(e) => e,
-                    Ok(cls) => PyErr::from_instance(py, cls),
+                    {
+                        Err(e) => e,
+                        Ok(cls) => PyErr::from_instance(py, cls),
+                    }
+            }
+        }
+    }
+}
+
+py_exception!(rustext, PatternError, RuntimeError);
+py_exception!(rustext, PatternFileError, RuntimeError);
+
+impl PatternError {
+    pub fn pynew(py: Python, inner: hg::PatternError) -> PyErr {
+        match inner {
+            hg::PatternError::UnsupportedSyntax(m) => {
+                PatternError::new(py, ("PatternError", m))
+            }
+        }
+    }
+}
+
+
+impl PatternFileError {
+    pub fn pynew(py: Python, inner: hg::PatternFileError) -> PyErr {
+        match inner {
+            hg::PatternFileError::IO(e) => {
+                let value = (
+                    e.raw_os_error().unwrap_or(2),
+                    e.to_string()
+                );
+                PyErr::new::<exc::IOError, _>(py, value)
+            }
+            hg::PatternFileError::Pattern(e, l) => {
+                match e {
+                    hg::PatternError::UnsupportedSyntax(m) =>
+                        PatternFileError::new(py, ("PatternFileError", m, l))
                 }
             }
         }