>>> def get_uniq_fields(lst, field_name):
...     return tuple({i[field_name]:None for i in lst})
... 
>>> def combine_fields(lst, field_name):
...     return sum(i[field_name] for i in lst)
... 
>>> def join_objects(lst):
...     out = []
...     names = get_uniq_fields(lst, 'name')
...     for name in names:
...         filtered_by_name = tuple(i for i in lst if i['name'] == name)
...         template = filtered_by_name[0]
...         count_combined = combine_fields(filtered_by_name, 'count')
...         some_combined = combine_fields(filtered_by_name, 'some')
...         template['count'] = count_combined
...         template['some'] = some_combined
...         out.append(template)
...     return out
... 
>>> lst = [{'name': 'Foo', 'size': 2, 'count': 1, 'some': 10},
...        {'name': 'Bar', 'size': 1, 'count': 3, 'some': 20},
...        {'name': 'Bar', 'size': 1, 'count': 2, 'some': 30}]
>>> 
>>> out = join_objects(lst)
>>> out
[{'name': 'Foo', 'size': 2, 'count': 1, 'some': 10}, {'name': 'Bar', 'size': 1, 'count': 5, 'some': 50}]
>>>

   
from typing import Dict, Tuple, Generator
  
class Summarizer:
  
    fields_to_sum = ["count"]
    unique_fields = ["name", "size"]
  
    def __init__(self):
        self._result: Dict[Tuple[str, ...], Tuple[int, ...]] = {}
  
    def add(self, record: Dict):
  
        uniques = tuple(record[i] for i in self.unique_fields)
        sums = tuple(record[i] for i in self.fields_to_sum)
        if sub_sums := self._result.get(uniques):
            sums = tuple(sum(i) for i in zip(sums, sub_sums))
        self._result[uniques] = sums
  
    @property
    def result(self) -> Generator[Dict, None, None]:
        for uniques, sums in self._result.items():
            _u = {k: v for k, v in zip(self.unique_fields, uniques)}
            _s = {k: v for k, v in zip(self.fields_to_sum, sums)}
            yield {**_u, **_s}
  
summarizer = Summarizer()
l = [{"name": "Foo", "size": 2, "count": 1},
     {"name": "Bar", "size": 1, "count": 3},
     {"name": "Bar", "size": 1, "count": 2}
     ]
  
for i in l:
    summarizer.add(i)
  
print(list(summarizer.result))

  
lst = [
    {'name': 'Foo', 'size': 2, 'count': 1},
    {'name': 'Bar', 'size': 1, 'count': 3},
    {'name': 'Bar', 'size': 1, 'count': 2}
]
new_dict = {}
for d in lst:
    k = (d['name'], d['size'])
    new_dict.setdefault(k, 0)
    new_dict[k] += d['count']
out = [{'name': k[0], 'size': k[1], 'count': v} for k, v in new_dict.items()]
print(out)

 
[{'name': 'Foo', 'size': 2, 'count': 1}, {'name': 'Bar', 'size': 1, 'count': 5}]

 import pandas as pd
data = [
{'name': 'Foo', 'size': 2, 'count': 1},
{'name': 'Bar', 'size': 1, 'count': 3},
{'name': 'Bar', 'size': 1, 'count': 2}
]
df = pandas.DataFrame(data)
out = df.groupby(['name', 'size'], as_index=False).sum('count').to_dict('records')
print(print)

 [
{'name': 'Bar', 'size': 1, 'count': 5},
{'name': 'Foo', 'size': 2, 'count': 1}
]