Key error on deployment - set comprehension issue?

I'm getting a key error when attempting to deploy my code.

I have isolated the issue to one of the functions, it seems to me that Chalice may not be able to understand set comprehensions?
My code works fine when running locally. It deploys fine when I comment out the function/route in question.

The line that seems to be causing my issues it this one:
`dynamodb_address_set |= {address_object['address'] for address_object in response.get('Items', [])}`

I was able to work around this issue by replacing that line with these two:
```
address_page_list = [address_object['address'] for address_object in response.get('Items', [])]
dynamodb_address_set |= set(address_page_list)
```

The full function causing the error is:

```
@app.route('/update_ips', methods=['POST', 'GET'])
def update_ips():
start_key = None
scan_kwargs = {}
dynamodb_address_set = set()
request = app.current_request
if request is not None and request.method == 'POST':
fields = request.json_body
prisma_ip_set = set(fields.get('ip_list'))

dynamodb = boto3.resource('dynamodb')
table = dynamodb.Table("prisma_addresses")
done = False
while not done:
if start_key:
scan_kwargs['ExclusiveStartKey'] = start_key
response = table.scan(**scan_kwargs)
dynamodb_address_set |= {address_object['address'] for address_object in response.get('Items', [])}
start_key = response.get('LastEvaluatedKey', None)
done = start_key is None
added_addresses = prisma_ip_set - dynamodb_address_set
removed_addresses = dynamodb_address_set - prisma_ip_set
for address in removed_addresses:
table.delete_item(Key={'address': address})
for address in added_addresses:
table.put_item(Item={'address': address})

return {
'current_addresses': prisma_ip_set,
'added_addresses': added_addresses,
'removed_addresses': removed_addresses,
'address_count': len(prisma_ip_set)
}

```
And the traceback I get when attempting to deploy is this:

```
PS prisma_bypass_reports> chalice deploy --stage prod
Traceback (most recent call last):
File "%projectpath%\venv\lib\site-packages\chalice\cli\__init__.py", line 636, in main
return cli(obj={})
File "%projectpath%\venv\lib\site-packages\click\core.py", line 1137, in __call__
return self.main(*args, **kwargs)
File "%projectpath%\venv\lib\site-packages\click\core.py", line 1062, in main
rv = self.invoke(ctx)
File "%projectpath%\venv\lib\site-packages\click\core.py", line 1668, in invoke
return _process_result(sub_ctx.command.invoke(sub_ctx))
File "%projectpath%\venv\lib\site-packages\click\core.py", line 1404, in invoke
return ctx.invoke(self.callback, **ctx.params)
File "%projectpath%\venv\lib\site-packages\click\core.py", line 763, in invoke
return __callback(*args, **kwargs)
File "%projectpath%\venv\lib\site-packages\click\decorators.py", line 26, in new_func
return f(get_current_context(), *args, **kwargs)
File "%projectpath%\venv\lib\site-packages\chalice\cli\__init__.py", line 189, in deploy
deployed_values = d.deploy(config, chalice_stage_name=stage)
File "%projectpath%\venv\lib\site-packages\chalice\deploy\deployer.py", line 376, in deploy
return self._deploy(config, chalice_stage_name)
File "%projectpath%\venv\lib\site-packages\chalice\deploy\deployer.py", line 386, in _deploy
self._build_stage.execute(config, resources)
File "%projectpath%\venv\lib\site-packages\chalice\deploy\deployer.py", line 652, in execute
step.handle(config, resource)
File "%projectpath%\venv\lib\site-packages\chalice\deploy\deployer.py", line 419, in handle
handler(config, resource)
File "%projectpath%\venv\lib\site-packages\chalice\deploy\deployer.py", line 637, in handle_autogeniampolicy
policy = self._policy_gen.generate_policy(config)
File "%projectpath%\venv\lib\site-packages\chalice\policy.py", line 93, in generate_policy
app_policy = policy_from_source_code(app_source)
File "%projectpath%\venv\lib\site-packages\chalice\policy.py", line 28, in policy_from_source_code
client_calls = get_client_calls_for_app(source_code)
File "%projectpath%\venv\lib\site-packages\chalice\analyzer.py", line 74, in get_client_calls_for_app
binder = t.bind_types()
File "%projectpath%\venv\lib\site-packages\chalice\analyzer.py", line 684, in bind_types
self.visit(self._parsed_code.parsed_ast)
File "C:\Program Files\Python38\lib\ast.py", line 360, in visit
return visitor(node)
File "C:\Program Files\Python38\lib\ast.py", line 368, in generic_visit
self.visit(item)
File "C:\Program Files\Python38\lib\ast.py", line 360, in visit
return visitor(node)
File "%projectpath%\venv\lib\site-packages\chalice\analyzer.py", line 694, in visit_FunctionDef
child_infer.bind_types()
File "%projectpath%\venv\lib\site-packages\chalice\analyzer.py", line 352, in bind_types
self.visit(self._current_ast_namespace)
File "%projectpath%\venv\lib\site-packages\chalice\analyzer.py", line 662, in visit
return ast.NodeVisitor.visit(self, node)
File "C:\Program Files\Python38\lib\ast.py", line 360, in visit
return visitor(node)
File "%projectpath%\venv\lib\site-packages\chalice\analyzer.py", line 540, in visit_FunctionDef
self.visit(child)
File "%projectpath%\venv\lib\site-packages\chalice\analyzer.py", line 662, in visit
return ast.NodeVisitor.visit(self, node)
File "C:\Program Files\Python38\lib\ast.py", line 360, in visit
return visitor(node)
File "C:\Program Files\Python38\lib\ast.py", line 368, in generic_visit
self.visit(item)
File "%projectpath%\venv\lib\site-packages\chalice\analyzer.py", line 662, in visit
return ast.NodeVisitor.visit(self, node)
File "C:\Program Files\Python38\lib\ast.py", line 360, in visit
return visitor(node)
File "C:\Program Files\Python38\lib\ast.py", line 370, in generic_visit
self.visit(value)
File "%projectpath%\venv\lib\site-packages\chalice\analyzer.py", line 662, in visit
return ast.NodeVisitor.visit(self, node)
File "C:\Program Files\Python38\lib\ast.py", line 360, in visit
return visitor(node)
File "C:\Program Files\Python38\lib\ast.py", line 370, in generic_visit
self.visit(value)
File "%projectpath%\venv\lib\site-packages\chalice\analyzer.py", line 662, in visit
return ast.NodeVisitor.visit(self, node)
File "C:\Program Files\Python38\lib\ast.py", line 360, in visit
return visitor(node)
File "C:\Program Files\Python38\lib\ast.py", line 370, in generic_visit
self.visit(value)
File "%projectpath%\venv\lib\site-packages\chalice\analyzer.py", line 662, in visit
return ast.NodeVisitor.visit(self, node)
File "C:\Program Files\Python38\lib\ast.py", line 360, in visit
return visitor(node)
File "%projectpath%\venv\lib\site-packages\chalice\analyzer.py", line 401, in visit_Name
self._symbol_table.get_inferred_type(node.id)
File "%projectpath%\venv\lib\site-packages\chalice\analyzer.py", line 249, in get_inferred_type
symbol = self._local_table.lookup(name)
File "C:\Program Files\Python38\lib\symtable.py", line 95, in lookup
flags = self._table.symbols[name]
KeyError: 'address_object'

```

Inspect chalice/analyzer.py around type binding for comprehensions, then follow how chalice/policy.py calls policy_from_source_code during deployment. Reproduce the KeyError with the shown update_ips function and verify that set comprehensions no longer make chalice deploy fail during policy generation.

Written by the indexing model from the issue text.