[GitHub] [airflow] uranusjr commented on a change in pull request #20184: Add and use `exactly_one` helper

[GitBox <gi...@apache.org>]

uranusjr commented on a change in pull request #20184:
URL: https://github.com/apache/airflow/pull/20184#discussion_r766202344



##########
File path: airflow/utils/helpers.py
##########
@@ -244,3 +244,18 @@ def build_airflow_url_with_query(query: Dict[str, Any]) -> str:
     view = conf.get('webserver', 'dag_default_view').lower()
     url = url_for(f"Airflow.{view}")
     return f"{url}?{parse.urlencode(query)}"
+
+
+def exactly_one(*args):
+    """
+    Returns True if exactly one of *args is "truthy", and False otherwise.
+    :param args:
+    :return:
+    """
+    has_one = False
+    for arg in args:
+        if arg and has_one:
+            return False
+        elif arg:
+            has_one = True
+    return has_one

Review comment:
       This can be problematic if the argument is of a type that can accept a falsy value, or if the default is not falsy (e.g. `NOTSET`). This should Can accept an optional `check_default=` keyword argument and check for default-ness with that instead (the default would be e.g. `functools.partial(operator.is_not, None)`).




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