如果计算都是示例那样两元素的加减乘除，那么可以使用如下代码

import re

d = {
'B': 2,
'C': 3,
}


def dict_calc(d: dict, text: str):
for line in text.splitlines(keepends=False):
sp = re.split(r'([=+\-*/])', line)
if len(sp) == 5:
sp = map(str.strip, sp)
a, eq, b, op, c = sp
if eq == '=' and op in '+-*/':
d[a] = eval(f'{d[b]}{op}{d[c]}')


dict_calc(d, '''
A = B + C
D = A - C
E = A * D
F = E / D
''')

print(d)
# Output:
# {'B': 2, 'C': 3, 'A': 5, 'D': 2, 'E': 10, 'F': 5.0}