[AIRFLOW-6686] Fix syntax error constructing list of process ids
diff --git a/airflow/utils/helpers.py b/airflow/utils/helpers.py
index 35da593c79c17..1f57f0b746cbe 100644
--- a/airflow/utils/helpers.py
+++ b/airflow/utils/helpers.py
@@ -211,7 +211,7 @@ def signal_procs(sig):
             # use sudo -n(--non-interactive) to kill the process
             if err.errno == errno.EPERM:
                 subprocess.check_call(
-                    ["sudo", "-n", "kill", "-" + str(sig)] + map(children, lambda p: str(p.pid))
+                    ["sudo", "-n", "kill", "-" + str(sig)] + [str(p.pid) for p in children]
                 )
             else:
                 raise

Construction of list of pids passed in kill command raises a Syntax error because
ordering of the arguments to `map` function doesn't conform to function
parameter definition.

A list comprehension replaces the existing `map` function to make the code
forward compatible with Python 3 and at the same time expand to a list of pids.

---
Issue link: [AIRFLOW-6686](https://issues.apache.org/jira/browse/AIRFLOW-6686)

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---
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