您试图将一个文件对象视为一个列表，并对其进行多次循环。如果不做额外的工作，那是行不通的。此外，您不会遍历一行的列；您正在尝试测试 整行 是否在其他 CSV 文件行中。您需要测试每个值，然后仅针对 search.file CSV 数据中行的最后一列。
文件对象有一个文件位置；当您从文件中读取时，位置会从开始移动到结束。一旦结束它不会自动再次移动到开始。
你可以重新开始寻找文件对象：
with open('newCIK.csv') as reader2_file:
reader2 = csv.reader(reader2_file)
with open('search.file') as f_in, open('SP500_10K.csv', 'w') as f_out:
reader = csv.reader(f_in, delimiter='|')
writer = csv.writer(f_out, delimiter='|')
for line in reader:
reader2_file.seek(0) # rewind to the start
for cik in reader2:
if cik in line:
writer.writerow(line)
但是，一遍又一遍地读取文件是慢。您最好在一开始就将整个内容读入内存。以上并没有解决另一个问题，即您正在测试来自newCIK.csv 的每一行，而不是每一列。
将 one 行读入内存，然后循环遍历：
with open('newCIK.csv', newline='') as reader2:
reader2 = csv.reader(reader2)
cik_values = next(reader2) # first row
with open('search.file', newline='') as f_in, open('SP500_10K.csv', 'w', newline='') as f_out:
reader = csv.reader(f_in, delimiter='|')
writer = csv.writer(f_out, delimiter='|')
for line in reader:
for cik in cik_values:
if cik in line[-1]: # test only the last column
writer.writerow(line)
请注意，我在open() 调用中添加了newline='' 参数； csv 模块需要更多地控制换行符；不这样做可能会在 Windows 上和处理包含换行符的值时导致问题。
演示：
>>> from io import StringIO
>>> import csv, sys
>>> newcik = '''\
... 66740,1800,1001463,1467373,896159
... '''
>>> search_file = '''\
... 1001385|NORTHWEST PIPE CO|10-Q|2015-05-06|edgar/data/1001385/0001193125-15-174814.txt
... 1001426|PERICOM SEMICONDUCTOR CORP|10-Q|2015-05-05|edgar/data/1001426/0001145443-15-000628.txt
... 1001463|Acacia Diversified Holdings, Inc.|10-K|2015-05-20|edgar/data/1001463/0001185185-15-001386.txt
... 1001463|Acacia Diversified Holdings, Inc.|10-K|2015-05-20|edgar/data/1001463/0001185185-15-001394.txt
... 1001463|Acacia Diversified Holdings, Inc.|10-Q|2015-05-20|edgar/data/1001463/0001185185-15-001388.txt
... 1001463|Acacia Diversified Holdings, Inc.|10-Q|2015-05-20|edgar/data/1001463/0001185185-15-001390.txt
... 1001463|Acacia Diversified Holdings, Inc.|10-Q|2015-05-20|edgar/data/1001463/0001185185-15-001392.txt
... 1001463|Acacia Diversified Holdings, Inc.|10-Q|2015-05-20|edgar/data/1001463/0001185185-15-001396.txt
... '''
>>> with StringIO(newcik) as reader2:
... reader2 = csv.reader(reader2)
... cik_values = next(reader2) # first row
...
>>> with StringIO(search_file) as f_in:
... reader = csv.reader(f_in, delimiter='|')
... writer = csv.writer(sys.stdout, delimiter='|')
... for line in reader:
... for cik in cik_values:
... if cik in line[-1]: # test only the last column
... writer.writerow(line)
...
1001463|Acacia Diversified Holdings, Inc.|10-K|2015-05-20|edgar/data/1001463/0001185185-15-001386.txt
103
1001463|Acacia Diversified Holdings, Inc.|10-K|2015-05-20|edgar/data/1001463/0001185185-15-001394.txt
103
1001463|Acacia Diversified Holdings, Inc.|10-Q|2015-05-20|edgar/data/1001463/0001185185-15-001388.txt
103
1001463|Acacia Diversified Holdings, Inc.|10-Q|2015-05-20|edgar/data/1001463/0001185185-15-001390.txt
103
1001463|Acacia Diversified Holdings, Inc.|10-Q|2015-05-20|edgar/data/1001463/0001185185-15-001392.txt
103
1001463|Acacia Diversified Holdings, Inc.|10-Q|2015-05-20|edgar/data/1001463/0001185185-15-001396.txt
103
103 数字是每个 writer.writerow() 调用中写入的字节数，由 REPL 回显。