orders=[(1,10),(2,20),(1,5)]
totals={}
for uid,amount in orders:
    totals[uid]=totals.get(uid,0)+amount
assert totals=={1:15,2:20}
print("totals",sorted(totals.items()))
values=[10,20,30,40]
assert values[1:3]==[20,30]
print("slice",values[1:3])
alias=values; alias.append(50)
assert values[-1]==50
rows=[[0]*3 for _ in range(2)]; rows[0][0]=9
assert rows[1][0]==0
codes=[" aa ","BB","aa"]
seen=set(); clean=[]
for item in codes:
    item=item.strip().upper()
    if item not in seen:
        seen.add(item); clean.append(item)
assert clean==["AA","BB"]
print("rows",rows,"unique codes",clean)