Pi In MongDB Aggregations

mongo_pi.py

from pymongo import MongoClient
from decimal import localcontext
from math import sqrt, log2
from bson import Decimal128
from bson.decimal128 import create_decimal128_context
coll = MongoClient().db.coll
coll.drop()
def Dec(x):
    with localcontext(create_decimal128_context()) as ctx:
        return Decimal128(ctx.create_decimal(x))
coll.insert_one({"x":Dec(1.0),"a":Dec(1.0),"b":Dec(1.0/sqrt(2.0)),"t":Dec(1.0/4),"y":Dec(1.0),})
[coll.update_one({}, [
    {"$set": {"y": {"$add": ["$a", 0.0]},},
    },{"$set": {"a": { "$divide": [ { "$add": [ "$a", "$b" ] },  2]},},
    },{"$set": {"b": { "$sqrt": [ { "$multiply": ["$b", "$y" ] }]},},
    },{"$set": {"t": { "$subtract": [ "$t", { "$multiply": ["$x", { "$pow": [ { "$subtract": ["$y", "$a"] }, 2]}]}]},},
    },{"$set": {"x": { "$multiply": [ "$x",  2]}},
}
]) for _ in range(int(log2(34)))]
coll.update_one({}, [{"$addFields": {"pi": {"$divide": [{"$pow": [{"$add": ["$a", "$b"]}, 2]}, {"$multiply": [4, "$t"]}]}}}])
print(coll.find_one({}, projection={"pi":1, "_id": 0}))

{'pi': Decimal128('3.141592653589793111200356215084374')}