Unexpected Jinja Template Behaviour in Custom Airflow Operator - airflow

Question

I have made a custom sensor in Airflow which inherits BashSensor.
Sensor :
class MySensor(BashSensor):
def __init__(self, time, **kwargs): # {{ ts }} is passed as time in the DAG
self.time = time
cmd = f"java some-other-stuff {self.time}" # rendered/correct value for self.time
super().__init__(**kwargs, bash_command=cmd)
def poke(self, context):
status = super().poke() # returns True or False
if status:
print(self.time) # {{ ts }} is printed instead of rendered value
else:
print("trying again")
return status
When I look at the rendered tab for the operator task in DAG I see bash_command has the correct rendered value ({{ ts }} is passed as time).
The problem is whenever poke is called and True is returned, I see {{ ts }} in the print statement instead of the rendered value.
I expect self.time to have the rendered value (some timestamp) not {{ ts }} when I print it in poke function.

Answer 1

Both cmd and time are not templated field in your code so Jinja engine does not handle them. The reason you see the command being templated is because in the super call you do:
bash_command=cmd
and bash_command is templated field of BashSensor
So while the command is parsed to the correct string as expected the individual components that created it does not contain the render value.
To explain in some more details: time = "{{ ds }}" will always stay as this string. it will never be rendered.
When you do cmd = f"java some-other-stuff {self.time}" it becomes:
"java some-other-stuff {{ ds }}"
This string is assigned to bash_command which is templated field and when the code is executed the value of {{ ds }} is rendered.
To solve your issue you can simply add the parameters you want to template to the sequence:
class MySensor(BashSensor):
...
template_fields: Sequence[str] = tuple({'time'} | set(BashSensor.template_fields))
...