How to pass variable to mongo pipeline from python

Working with Data
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9

i have pipeline in mongodb as below
pipeline = [{"$match": {"_id": “${var_id}”, “date”: ${“todaysdate}” }]

in python i have retrieved the above pipeline from mongo and stored in variable

Now, srcQuerry=[{"$match": {"_id": “${var_id}”, “date”: ${“todaysdate}” }]

now i am using aggreagate

result = collection.aggregate(srcQuery)

how to pass value to var_id and date from srcQuery??