Cryptic TypeError in proto-plus during assignment with invalid type

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
72/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Quiet
Tech stack
python
Domain
backend-api-design

Research direction

Start in proto/message.py at setattr around the reported MergeFrom call, then trace the initialization and MergeFrom paths mentioned in the issue. Reproduce the sample assignment with batch.pyspark_batch.args = [1000] and verify that the resulting TypeError identifies the PysparkBatch message, the args field, and the invalid value.

Written by the indexing model from the issue text.

Description

priority: p3 type: docs
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Summary of the issue

Context:
When setting a field on a protobuf message using proto-plus with an invalid type or structure, the underlying protocol buffer library fails during initialization or merging.

Expected Behavior:
proto-plus should catch the TypeError and re-raise it with a more descriptive message that includes the specific message class and field name, aiding in debugging type mismatches.

Actual Behavior:
The library raises a cryptic TypeError: bad argument type for built-in operation without any context about which field or message class caused the failure.

API client name and version

proto-plus

Reproduction steps: code

from google.cloud import dataproc_v1

def sample_create_batch():
batch = dataproc_v1.Batch()

# Provide a type that is not a string in the args list. args expects a MutableSequence[str]
batch.pyspark_batch.args = [1000]

sample_create_batch()

Reproduction steps: supporting files

file: mydata.csv

alpha,1,3
beta,2,5
Reproduction steps: actual results

Traceback (most recent call last):
File "test.py", line 42, in
sample_create_batch()
File "test.py", line 24, in sample_create_batch
batch.pyspark_batch.args = [1000 ]
File "/env/lib/python3.11/site-packages/proto/message.py", line 944, in setattr
self._pb.MergeFrom(self._meta.pb(**{key: pb_value}))
TypeError: bad argument type for built-in operation

Reproduction steps: expected results

TypeError: Failed to set field 'args' on PysparkBatch with value [1000]. Underlying error: bad argument type for built-in operation.

OS & version + platform

Linux (Google Cloud Shell) / macOS

Python environment

Python 3.12

Python dependencies

No response

Additional context

The cryptic error is thrown directly from the underlying protocol buffers MergeFrom execution inside proto/message.py. Wrapping the initialization and MergeFrom calls in try-except blocks to provide contextual wrapper errors would greatly improve the developer experience.

Dominant language
Python
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