feat: improve error group tracebacks on < py11 (#825)

google/cloud/bigtable/data/exceptions.py

@@ -74,7 +74,44 @@ def __init__(self, message, excs):
             if len(excs) == 0:
                 raise ValueError("exceptions must be a non-empty sequence")
             self.exceptions = tuple(excs)
-            super().__init__(message)
+            # simulate an exception group in Python < 3.11 by adding exception info
+            # to the message
+            first_line = "--+----------------  1 ----------------"
+            last_line = "+------------------------------------"
+            message_parts = [message + "\n" + first_line]
+            # print error info for each exception in the group
+            for idx, e in enumerate(excs[:15]):
+                # apply index header
+                if idx != 0:
+                    message_parts.append(
+                        f"+---------------- {str(idx+1).rjust(2)} ----------------"
+                    )
+                cause = e.__cause__
+                # if this exception was had a cause, print the cause first
+                # used to display root causes of FailedMutationEntryError and  FailedQueryShardError
+                # format matches the error output of Python 3.11+
+                if cause is not None:
+                    message_parts.extend(
+                        f"| {type(cause).__name__}: {cause}".splitlines()
+                    )
+                    message_parts.append("| ")
+                    message_parts.append(
+                        "| The above exception was the direct cause of the following exception:"
+                    )
+                    message_parts.append("| ")
+                # attach error message for this sub-exception
+                # if the subexception is also a _BigtableExceptionGroup,
+                # error messages will be nested
+                message_parts.extend(f"| {type(e).__name__}: {e}".splitlines())
+            # truncate the message if there are more than 15 exceptions
+            if len(excs) > 15:
+                message_parts.append("+---------------- ... ---------------")
+                message_parts.append(f"| and {len(excs) - 15} more")
+            if last_line not in message_parts[-1]:
+                # in the case of nested _BigtableExceptionGroups, the last line
+                # does not need to be added, since one was added by the final sub-exception
+                message_parts.append(last_line)
+            super().__init__("\n  ".join(message_parts))
 
     def __new__(cls, message, excs):
         if is_311_plus:
@@ -83,11 +120,19 @@ def __new__(cls, message, excs):
             return super().__new__(cls)
 
     def __str__(self):
+        if is_311_plus:
+            # don't return built-in sub-exception message
+            return self.args[0]
+        return super().__str__()
+
+    def __repr__(self):
         """
-        String representation doesn't display sub-exceptions. Subexceptions are
-        described in message
+        repr representation should strip out sub-exception details
         """
-        return self.args[0]
+        if is_311_plus:
+            return super().__repr__()
+        message = self.args[0].split("\n")[0]
+        return f"{self.__class__.__name__}({message!r}, {self.exceptions!r})"
 
 
 class MutationsExceptionGroup(_BigtableExceptionGroup):
@@ -200,14 +245,12 @@ def __init__(
         idempotent_msg = (
             "idempotent" if failed_mutation_entry.is_idempotent() else "non-idempotent"
         )
-        index_msg = f" at index {failed_idx} " if failed_idx is not None else " "
-        message = (
-            f"Failed {idempotent_msg} mutation entry{index_msg}with cause: {cause!r}"
-        )
+        index_msg = f" at index {failed_idx}" if failed_idx is not None else ""
+        message = f"Failed {idempotent_msg} mutation entry{index_msg}"
         super().__init__(message)
+        self.__cause__ = cause
         self.index = failed_idx
         self.entry = failed_mutation_entry
-        self.__cause__ = cause
 
 
 class RetryExceptionGroup(_BigtableExceptionGroup):
@@ -217,10 +260,8 @@ class RetryExceptionGroup(_BigtableExceptionGroup):
     def _format_message(excs: list[Exception]):
         if len(excs) == 0:
             return "No exceptions"
-        if len(excs) == 1:
-            return f"1 failed attempt: {type(excs[0]).__name__}"
-        else:
-            return f"{len(excs)} failed attempts. Latest: {type(excs[-1]).__name__}"
+        plural = "s" if len(excs) > 1 else ""
+        return f"{len(excs)} failed attempt{plural}"
 
     def __init__(self, excs: list[Exception]):
         super().__init__(self._format_message(excs), excs)
@@ -268,8 +309,8 @@ def __init__(
         failed_query: "ReadRowsQuery" | dict[str, Any],
         cause: Exception,
     ):
-        message = f"Failed query at index {failed_index} with cause: {cause!r}"
+        message = f"Failed query at index {failed_index}"
         super().__init__(message)
+        self.__cause__ = cause
         self.index = failed_index
         self.query = failed_query
-        self.__cause__ = cause