What is the reason why pipeline persistent storage files cannot be written when using Scapy crawler?

Scapy crawler data persistence: Analysis of the causes of failure to write pipeline files and solutions

This article analyzes the common problem that files cannot be written to data when using pipelines for persistent storage in Scapy crawlers. The problem usually stems from a pipeline class method definition error, resulting in the file pointer not being initialized correctly.

Question description:

When a user writes a crawler using Scapy, he tries to write crawl data to a file using a custom pipeline, but the file is always empty. The error message prompts TypeError: object of type qiubaiitem is not JSON serializable and AttributeError: 'NoneType' object has no attribute 'close' , indicating that the data type is wrong and the file pointer is not initialized.

Code Analysis:

In the code snippet provided by the user, there is a key error in the pipelines.py file: the open_spdier method name is spelled incorrectly, and should be open_spider . The Scrapy framework cannot recognize the wrongly spelled function name, causing self.fp to always be None , which in turn causes file writing to fail.

Error code (pipelines.py):

 class qiubaipipeline(object):
    def __init__(self):
        self.fp = None

    def open_spdier(self, spider): # Error: open_spdier should be open_spider
        print("Start crawler")
        self.fp = open('./biedou.txt', 'w', encoding='utf-8')

    def close_spider(self, spider):
        print("End Crawler")
        self.fp.close()

    def process_item(self, item, spider):
        title = str(item['title'])
        content = str(item['content'])
        self.fp.write(title ':' content '\n')
        return item

Corrected code (pipelines.py):

 class QiubaiPipeline(object): # It is recommended that class name initial letter capital def __init__(self):
        self.fp = None

    def open_spider(self, spider):
        print("Start crawler")
        self.fp = open('./biedou.txt', 'w', encoding='utf-8')

    def close_spider(self, spider):
        print("End Crawler")
        self.fp.close()

    def process_item(self, item, spider):
        title = str(item['title'])
        content = str(item['content'])
        self.fp.write(title ':' content '\n')
        return item

Solution:

1. Correction method name: Correct open_spdier to open_spider .
2. Error handling: It is recommended to add an error handling mechanism, such as try...except block, to gracefully handle exceptions that may occur during file opening and writing.
3. Class name specification: It is recommended to use class names that comply with Python specifications, such as QiubaiPipeline .

With the above correction, the Scapy crawler's pipeline can correctly write data to the file. Remember to double-check spelling errors in your code, which is often the source of difficult problems.

The above is the detailed content of What is the reason why pipeline persistent storage files cannot be written when using Scapy crawler?. For more information, please follow other related articles on the PHP Chinese website!