试图通过示例代码了解生成器

Question

我试图通过将分隔符“管道”的文件转换为csv文件（3个文件）来了解生成器的工作原理。

当我运行以下代码时，它仅转换和写入1个csv文件（c.csv）。

我期望它将转换并写入所有三个文件（a.csv，b.csv和c.csv）

专家，您能帮我理解为什么它不能转换3个文件吗？

每个文件中的数据（3个文件）：

country|city

代码：

from typing import Iterator, Iterable

ret={
  "data": [
    {
      "src": "/Users/home/Desktop/python/a.txt"
    },
     {
      "src": "/Users/home/Desktop/python/b.txt"
    },
    {
      "src": "/Users/home/Desktop/python/c.txt"
    }]}

def extract(files:Iterable[dict])-> Iterator[dict]:
    for file in files:
        ret = file.copy()
        with open(file['src']) as f:    
            ret['data']=f.read()
    yield ret

def transform(files: Iterable[dict]) -> Iterator[dict]:
    for file in files:

        df = file_to_df(file["data"])
        ret = file.copy()
        ret['data']=df
        yield ret

def load(files: Iterable[dict]) -> Iterator[dict]:
    for file in files:
        f = open(file['src'].replace(".txt",".csv"),'w')
        f.write(file['data'])
        ret = dict(file)
        ret['dest']=file['src'].replace(".txt",".csv")
        yield ret

# Convert pipe to comma

def file_to_df (file:str, boilerplate_stripped=False):
    df = file.replace("|",",")
    return df

# Transform pipe delimited files to csv

raw_files = extract(ret['data'])   
transform_files = transform(raw_files)
load_files = load(transform_files)   

keep_keys = ['src', 'dest']
ret = {
        "data": [dict({k: v for k, v in x.items() if k in keep_keys}) for x in load_files]
    }

print (ret)

结果：

{'data': [{'src': '/Users/home/Desktop/python/c.txt', 'dest': '/Users/home/Desktop/python/c.csv'}]}

预期结果：

{'data': [{'src': '/Users/home/Desktop/python/a.txt', 'dest': '/Users/home/Desktop/python/a.csv'},
          {'src': '/Users/home/Desktop/python/b.txt', 'dest': '/Users/home/Desktop/python/b.csv'},
          {'src': '/Users/home/Desktop/python/c.txt', 'dest': '/Users/home/Desktop/python/c.csv'}]}