from collections import defaultdict

s = 'mississippi'
d = defaultdict(int)
for k in s:
 d[k] += 1
print(d)

# 输出
# defaultdict(<class 'int'>, {'m': 1, 'i': 4, 's': 4, 'p': 2})

s = 'mississippi'
d = {}
for k in s:
 if k not in d:
  d[k] = 1
 else:
  d[k] = d[k] + 1
print(d)

# 输出
# {'m': 1, 'i': 4, 's': 4, 'p': 2}

s = [('yellow', 1), ('blue', 2), ('yellow', 3), ('blue', 4), ('red', 1)]
d = defaultdict(list)
for k, v in s:
 d[k].append(v)
print(d)

# 输出
# defaultdict(<class 'list'>, {'yellow': [1, 3], 'blue': [2, 4], 'red': [1]})

q = defaultdict(lambda: [0, 0, 0])
print(q['a'])

# 输出
# [0, 0, 0]