[英]Read CSV over FTP line by line without storing the whole file in memory/disk
I'm stuck piping ftplib.FTP.retrlines
to csv.reader
...我被困在管道
ftplib.FTP.retrlines
到csv.reader
...
FTP.retrlines
repeatedly calls a callback with a line in it, while csv.reader
expects an iterator which returns a string each time its __next__()
method is called. FTP.retrlines
重复调用包含一行的回调,而csv.reader
需要一个迭代器,每次调用其__next__()
方法时都会返回一个字符串。
How do I combine the two things together so that I can read and process the file without reading the whole file in advance and eg storing it in a eg io.TextIOWrapper
?如何将这两件事结合在一起,以便我可以读取和处理文件而无需提前读取整个文件,例如将其存储在例如
io.TextIOWrapper
?
My problem is FTP.retrlines
won't return until it consumed the whole file...我的问题是
FTP.retrlines
在消耗整个文件之前不会返回...
I'm not sure if there's not a better solution, but you can glue the FTP.retrlines
and csv.reader
together using iterable queue-like object.我不确定是否没有更好的解决方案,但是您可以使用类似可迭代队列的 ZA8CFDE6331BD59EB2AC96F8911C4B66Z6 将
FTP.retrlines
和csv.reader
在一起。 And as both the functions are synchronous, you have to run them on different threads in parallel.由于这两个函数都是同步的,因此您必须在不同的线程上并行运行它们。
Something like this:像这样的东西:
from queue import Queue
from ftplib import FTP
from threading import Thread
import csv
ftp = FTP(host)
ftp.login(username, password)
class LineQueue:
_queue = Queue(10)
def add(self, s):
print(f"Queueing line {s}")
self._queue.put(s)
print(f"Queued line {s}")
def done(self):
print("Signaling Done")
self._queue.put(False)
print("Signaled Done")
def __iter__(self):
print("Reading lines")
while True:
print("Reading line")
s = self._queue.get()
if s == False:
print("Read all lines")
break
print(f"Read line {s}")
yield s
q = LineQueue()
def download():
ftp.retrlines("RETR /path/data.csv", q.add)
q.done()
thread = Thread(target=download)
thread.start()
print("Reading CSV")
for entry in csv.reader(q):
print(entry)
print("Read CSV")
thread.join()
Same solution as Martin's , just saved some line of code subclassing queue.Queue
directly.与Martin 的解决方案相同,只是直接保存了一些代码行子类
queue.Queue
。
from queue import Queue
from ftplib import FTP
from threading import Thread
import csv
ftp = FTP(**ftp_credentials)
class LineQueue(Queue):
def __iter__(self):
while True:
s = self.get()
if s is None:
break
yield s
def __call__(self):
ftp.retrlines(f"RETR {fname}", self.put)
self.put(None)
q = LineQueue(10)
thread = Thread(target=q)
thread.start()
for entry in csv.reader(q):
print(entry)
thread.join()
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