请教大神们，为什么这段代码啥也运行不出来，也不报错

Question

import re
a = open(r'E:\python课程\130\03_python-network-data\quiz & assignments\Chapter11\regex_sum_75422.txt')
f = []
total = 0
for c in a:
d = re.findall('[0-9]+',c)

for e in d:
    f = d.append(int(e))

print(sum(f))

Answer 1

应该是：
```for e in d:
f.append(int(e))