Stop swallowing exceptions

src/lib.rs

@@ -515,14 +515,20 @@ impl Log for Logger {
         let cache = self.lookup(record.target());
 
         if self.enabled_inner(record.metadata(), &cache) {
-            Python::with_gil(|py| match self.log_inner(py, record, &cache) {
+            Python::with_gil(|py| {
+                // If an exception were triggered before this attempt to log, 
+                // store it to the side for now and restore it afterwards.
+                let maybe_existing_exception = PyErr::take(py);
+                match self.log_inner(py, record, &cache) {
+
                 Ok(Some(logger)) => {
                     let filter = match self.caching {
                         Caching::Nothing => unreachable!(),
                         Caching::Loggers => LevelFilter::max(),
                         Caching::LoggersAndLevels => extract_max_level(logger.bind(py))
                             .unwrap_or_else(|e| {
-                                e.print(py);
+                                // See detailed NOTE below
+                                e.restore(py);
                                 LevelFilter::max()
                             }),
                     };
@@ -531,8 +537,19 @@ impl Log for Logger {
                     self.store_to_cache(py, record.target(), entry);
                 }
                 Ok(None) => (),
-                Err(e) => e.print(py),
-            })
+                Err(e) => {
+                    // NOTE: If an exception was triggered _during_ logging, restore it as current Python exception.
+                    // We have to use PyErr::restore because we cannot return a PyResult from the Log trait's log method.
+                    e.restore(py);
+                },
+            };
+
+            // If there was a prior exception, restore it now
+            // This ensures that the earliest thrown exception will be the one that's visible to the caller.
+            if let Some(e) = maybe_existing_exception {
+                e.restore(py);
+            }
+        })
         }
     }