feat: add type hints for public methods (#613)

* feat: add type hint for public methods

* feat: add bigquery-storage in requirement file

* feat: add pandas in requirement file

* feat: add return type hint

* feat: remove pandas import as a string

* Use the latest pytype version (2021.4.9)

* Silence false import and module attribute errors

* Fix misc. pytype warnings and false postiives

* Make changes to generated files persistent

* Make final cleanup of client.py

* Change import ignores to more specific errors

* Silence false positive type warning in job config

* Silence noisy _helper type warnings

* Silence false positives for resumable media code

* Add pytype to nox.options.sessions

* Hide for-type-check-only imports behind a flag

* Remove obsolete skipIf decorator from two tests

inspect.signature() was added in Python 3.3, and the library only
needs to suppport Python3.6+.

* Install dependencies in pytype session

This avoids numerous unnecessary import and module attribute errors,
rendering lots of pytype directive comments obsolete.

* Be more specific about to_dataframe()'s return type

* Add missing return type for _get_query_results()

* Be more specific about pandas/pyarrow return types

* Exclude typing-only imports from coverage checks

Co-authored-by: HemangChothani <hemang.chothani@qlogic.io>
Co-authored-by: Tim Swast <swast@google.com>

.gitignore

@@ -29,6 +29,7 @@ pip-log.txt
 .nox
 .cache
 .pytest_cache
+.pytype
 
 
 # Mac

google/cloud/bigquery/_http.py

@@ -17,8 +17,7 @@
 import os
 import pkg_resources
 
-from google.cloud import _http
-
+from google.cloud import _http  # pytype: disable=import-error
 from google.cloud.bigquery import __version__
 
 

google/cloud/bigquery/_pandas_helpers.py

@@ -373,6 +373,7 @@ def augment_schema(dataframe, current_bq_schema):
     Returns:
         Optional[Sequence[google.cloud.bigquery.schema.SchemaField]]
     """
+    # pytype: disable=attribute-error
     augmented_schema = []
     unknown_type_fields = []
 
@@ -406,6 +407,7 @@ def augment_schema(dataframe, current_bq_schema):
         return None
 
     return augmented_schema
+    # pytype: enable=attribute-error
 
 
 def dataframe_to_arrow(dataframe, bq_schema):