Fix import handling by lazy loading hooks introduced in PR #1109 (#1132)

Making an update to #1109, which introduced module-level imports of
optional dependencies. This is inappropriate as it will break if the
user does not have them installed, and indeed the user really does not
need them installed if they are not relying on them directly.

This PR lazy-loads the imports so that it does not impact users who do
not need them.

In the upath library, `az:`, `adl:`, `abfs:` and `abfss:` are also all valid schemes, 
albeit Airflow only references the latter 3 in the code: https://github.com/apache/airflow/blob/e3824eaaba7eada9a807f7a2f9f89d977a210e15/airflow/providers/microsoft/azure/fs/adls.py#L29, so `adl:`, `abfs:` and `abfss:` also have been added
to the list of schemes supported.

cosmos/config.py

@@ -184,7 +184,7 @@ def __init__(
             if not manifest_conn_id:
                 manifest_scheme = manifest_path_str.split("://")[0]
                 # Use the default Airflow connection ID for the scheme if it is not provided.
-                manifest_conn_id = FILE_SCHEME_AIRFLOW_DEFAULT_CONN_ID_MAP.get(manifest_scheme, None)
+                manifest_conn_id = FILE_SCHEME_AIRFLOW_DEFAULT_CONN_ID_MAP.get(manifest_scheme, lambda: None)()
 
             if manifest_conn_id is not None and not AIRFLOW_IO_AVAILABLE:
                 raise CosmosValueError(

cosmos/constants.py

@@ -1,11 +1,9 @@
 import os
 from enum import Enum
 from pathlib import Path
+from typing import Callable, Dict
 
 import aenum
-from airflow.providers.amazon.aws.hooks.s3 import S3Hook
-from airflow.providers.google.cloud.hooks.gcs import GCSHook
-from airflow.providers.microsoft.azure.hooks.wasb import WasbHook
 from packaging.version import Version
 
 DBT_PROFILE_PATH = Path(os.path.expanduser("~")).joinpath(".dbt/profiles.yml")
@@ -31,14 +29,30 @@
 PARTIALLY_SUPPORTED_AIRFLOW_VERSIONS = [Version("2.9.0"), Version("2.9.1")]
 
 
-S3_FILE_SCHEME = "s3"
-GS_FILE_SCHEME = "gs"
-ABFS_FILE_SCHEME = "abfs"
+def _default_s3_conn() -> str:
+    from airflow.providers.amazon.aws.hooks.s3 import S3Hook
 
-FILE_SCHEME_AIRFLOW_DEFAULT_CONN_ID_MAP = {
-    S3_FILE_SCHEME: S3Hook.default_conn_name,
-    GS_FILE_SCHEME: GCSHook.default_conn_name,
-    ABFS_FILE_SCHEME: WasbHook.default_conn_name,
+    return S3Hook.default_conn_name  # type: ignore[no-any-return]
+
+
+def _default_gcs_conn() -> str:
+    from airflow.providers.google.cloud.hooks.gcs import GCSHook
+
+    return GCSHook.default_conn_name  # type: ignore[no-any-return]
+
+
+def _default_wasb_conn() -> str:
+    from airflow.providers.microsoft.azure.hooks.wasb import WasbHook
+
+    return WasbHook.default_conn_name  # type: ignore[no-any-return]
+
+
+FILE_SCHEME_AIRFLOW_DEFAULT_CONN_ID_MAP: Dict[str, Callable[[], str]] = {
+    "s3": _default_s3_conn,
+    "gs": _default_gcs_conn,
+    "adl": _default_wasb_conn,
+    "abfs": _default_wasb_conn,
+    "abfss": _default_wasb_conn,
 }