تجميع العناصر بإستخدام defaultdict

from collections import defaultdict

groups = defaultdict(list)
for name in ["Ahmed", "Ali", "Mona"]:
    groups[name[0]].append(name)
print(dict(groups))

{'A': ['Ahmed', 'Ali'], 'M': ['Mona']}

from collections import defaultdict

totals = defaultdict(int)
for category, amount in [("books", 10), ("pens", 5), ("books", 20)]:
    totals[category] += amount
print(dict(totals))

{'books': 30, 'pens': 5}