assignments of dict list is not supported for repeated field

[arithmetic1728]

How to reproduce:

1. Clone https://github.com/googleapis/python-vision, switch to proto_issue branch, then install it locally.
2. Run the following sample.

from google.cloud import vision_v1
import proto
import json

request = dict(image=vision_v1.Image(content=b"content"))
batch_req = vision_v1.BatchAnnotateImagesRequest()

# This works (converting the dict to AnnotateImageRequest first, then form a list)
# batch_req.requests = [vision_v1.AnnotateImageRequest(request)]

# This throws exception (assigning the list of dict directly)
batch_req.requests = [request]

The last line throws the following exceptions:

TypeError: Parameter to MergeFrom() must be instance of same class: expected google.cloud.vision.v1.Image got Image.

[software-dov]

The workaround is to not assign repeated fields from lists of dicts.

The following should work:

from google.cloud import vision_v1

request = dict(image=vision_v1.Image(content=b"content"))
batch_req = vision_v1.BatchAnnotateImagesRequest()
batch_req.requests = [request]

Or to use the indirect method described in the issue text above.

Dropping priority to P3 since workarounds exist.

[parthea]

I can no longer reproduce this issue. Please open a new issue if you're still experiencing the problem.