当我在Python中插入2行时，为什么会得到无限循环？

Question

while True:
    print ("test")
    sleep(3)
    try:
        doc = html.fromstring(page.content)
        XPATH_NAME = '//h1[@id="title"]//text()'
        XPATH_SALE_PRICE = '//span[contains(@id,"priceblock_ourprice") or contains(@id,"saleprice")]/text()'
        XPATH_ORIGINAL_PRICE = '//td[contains(text(),"List Price") or contains(text(),"M.R.P") or contains(text(),"Price")]/following-sibling::td/text()'
        XPATH_CATEGORY = '//a[@class="a-link-normal a-color-tertiary"]//text()'
        XPATH_AVAILABILITY = '//div[@id="availability"]//text()'

        RAW_NAME = doc.xpath(XPATH_NAME)
        RAW_SALE_PRICE = doc.xpath(XPATH_SALE_PRICE)
        RAW_CATEGORY = doc.xpath(XPATH_CATEGORY)
        RAW_ORIGINAL_PRICE = doc.xpath(XPATH_ORIGINAL_PRICE)
        RAw_AVAILABILITY = doc.xpath(XPATH_AVAILABILITY)
        print(RAW_SALE_PRICE)

        NAME = ' '.join(''.join(RAW_NAME).split()) if RAW_NAME else None
        SALE_PRICE = ' '.join(''.join(RAW_SALE_PRICE).split()).strip() if RAW_SALE_PRICE else None
        CATEGORY = ' > '.join([i.strip() for i in RAW_CATEGORY]) if RAW_CATEGORY else None
        ORIGINAL_PRICE = ''.join(RAW_ORIGINAL_PRICE).strip() if RAW_ORIGINAL_PRICE else None
        AVAILABILITY = ''.join(RAw_AVAILABILITY).strip() if RAw_AVAILABILITY else None
        print(SALE_PRICE)

        if not ORIGINAL_PRICE:
            ORIGINAL_PRICE = SALE_PRICE


        data = {
            'NAME': NAME,
            'SALE_PRICE': SALE_PRICE,
            'CATEGORY': CATEGORY,
            'ORIGINAL_PRICE': ORIGINAL_PRICE,
            'AVAILABILITY': AVAILABILITY,
            'URL': url,
        }

        return data
    except Exception as e:
        print
        e

This works perfectly fine. But when I insert

if SALE_PRICE.startswith('EUR'):
                SALE_PRICE = SALE_PRICE.replace('EUR ', '')

after the Lins where I Strip the RAW Variables into the normal Variables (NAME,SALE_PRICE) then I will end in a infitine loop - why?

Answer 1

See the line:

SALE_PRICE = ' '.join(''.join(RAW_SALE_PRICE).split()).strip() if RAW_SALE_PRICE else None

here SALE_PRICE can be assigned a None value. When you add your lines you are in some cases attempting to do .startswith on a None value. That will lead to an exception. In your exception clause you do not break the loop and it will continue forever.

Add a break or return to your exception clause.

Answer 2

Take try catch block outside of while loop, in other words while to be nested within try, something like this

try:
  while(true):
    #All your code
except Exception as e:
   print e