Python:无法启动新线程。我可以错开或延迟一些线程吗？

Question

不太确定如何问这个问题，因为我刚刚开始学习 python，但这里是这样的:

我有一个使用线程来抓取信息的网络抓取器。我正在寻找大约 900 种产品的定价和库存。当我用大约一半的脚本测试脚本时，没有问题。当我尝试抓取所有 900 种产品时，出现无法启动新线程的错误。

我想这是由于某些内存限制造成的，或者是因为我向服务器请求了太多请求

我想知道是否有办法减慢线程速度或错开请求。

错误代码:

Traceback (most recent call last):
  File "C:\Python27\tests\dxpriceupdates.py", line 78, in <module>
    t.start()
error: can't start new thread
>>> 
Traceback (most recent call last):Exception in thread Thread-554:
Traceback (most recent call last):
  File "C:\Python27\lib\urllib.py", line 346, in open_http
    errcode, errmsg, headers = h.getreply()
  File "C:\Python27\lib\httplib.py", line 1117, in getreply
    response = self._conn.getresponse()
  File "C:\Python27\lib\httplib.py", line 1045, in getresponse
    response.begin()
  File "C:\Python27\lib\httplib.py", line 441, in begin
    self.msg = HTTPMessage(self.fp, 0)
  File "C:\Python27\lib\mimetools.py", line 25, in __init__
    rfc822.Message.__init__(self, fp, seekable)
  File "C:\Python27\lib\rfc822.py", line 108, in __init__
    self.readheaders()
  File "C:\Python27\lib\httplib.py", line 308, in readheaders
    self.addheader(headerseen, line[len(headerseen)+1:].strip())
MemoryError

<bound method Thread.__bootstrap of <Thread(Thread-221, stopped 9512)>>Traceback (most recent call last):
Traceback (most recent call last):
Traceback (most recent call last):

Traceback (most recent call last):
Unhandled exception in thread started by Unhandled exception in thread started by ...

这是 python(skulist.txt 只是一个文本文件，如 12345、23445、5551...):

from threading import Thread
import urllib
import re
import json
import math    

def th(ur):
    site = "http://dx.com/p/GetProductInfoRealTime?skus="+ur
    htmltext = urllib.urlopen(site)
    data = json.load(htmltext)
    htmlrates = urllib.urlopen("http://rate-exchange.appspot.com/currency?from=USD&to=AUD")
    datarates = json.load(htmlrates)
    if data['success'] == True:
        if data['data'][0]['discount'] is 0:
            price = float(data['data'][0]['price'])
            rate = float(datarates['rate']) + 0.12
            cost = price*rate
            if cost <= 5:
                saleprice = math.ceil(cost*1.7) - .05
            elif (cost >5) and (cost <= 10):
                saleprice = math.ceil(cost*1.6) - .05
            elif (cost >10) and (cost <= 15):
                saleprice = math.ceil(cost*1.55) - .05
            else:
                saleprice = math.ceil(cost*1.5) - .05
            if data['data'][0]['issoldout']:
                soldout = "Out Of Stock"
                enabled = "Disable"
                qty = "0"
            else:
                soldout = "In Stock"
                enabled = "Enabled"
                qty = "9999"
            
            #print model, saleprice, soldout, qty, enabled
            myfile.write(str(ur)+","+str(saleprice)+","+str(soldout)+","+str(qty)+","+str(enabled)+"\n")
        else:
            price = float(data['data'][0]['listprice'])
            rate = float(datarates['rate']) + 0.12
            cost = price*rate
            if cost <= 5:
                saleprice = math.ceil(cost*1.7) - .05
            elif (cost >5) and (cost <= 10):
                saleprice = math.ceil(cost*1.6) - .05
            elif (cost >10) and (cost <= 15):
                saleprice = math.ceil(cost*1.55) - .05
            else:
                saleprice = math.ceil(cost*1.5) - .05
            if data['data'][0]['issoldout']:
                soldout = "Out Of Stock"
                enabled = "Disable"
                qty = "0"
            else:
                soldout = "In Stock"
                enabled = "Enabled"
                qty = "9999"
           
            #print model, saleprice, soldout, qty, enabled
            myfile.write(str(ur)+","+str(saleprice)+","+str(soldout)+","+str(qty)+","+str(enabled)+"\n")
    else:
        qty = "0"
        print ur, "error \n"
        myfile.write(str(ur)+","+"0.00"+","+"Out Of Stock"+","+str(qty)+","+"Disable\n")
         

skulist = open("skulist.txt").read()
skulist = skulist.replace(" ", "").split(",")

myfile = open("prices/price_update.txt", "w+")
myfile.close()

myfile = open("prices/price_update.txt", "a")
threadlist = []

for u in skulist:
    t = Thread(target=th,args=(u,))
    t.start()
    threadlist.append(t)

for b in threadlist:
    b.join()
  
myfile.close()

Answer 1

不要同时触发 900 个线程，您的 PC 可能会窒息!相反，使用池并将事件分配给一定数量的 worker 。像这样使用 multiprocessing:

from multiprocessing import Pool

WORKERS = 10
p = Pool(WORKERS)
p.map(tr, skulist)

通过一些试验为 WORKERS 找到正确的值。