寻找另一种避免 if 语句的方法

Question

我是 Python 语言的新手，我开始使用 Scrapy，这太棒了，我想知道是否有任何方法可以减少编写代码并避免大量 if 语句也避免代码中的重复：

titleText = response.css('title::text').get()

    if response.status == 200:
        if len(response.css('title').extract()) == 0:
            self.data['crawl']['meta']['missingTitle'].append({
                'url': response.url,
                'latency': response.meta.get('download_latency')
            })
        elif len(response.css('title').extract()) == 1:
            if len(titleText) > 70:
                self.data['crawl']['meta']['longTitle'].append({
                    'url': response.url,
                    'text': titleText,
                    'latency': response.meta.get('download_latency')
                })
            elif len(titleText) < 50:
                self.data['crawl']['meta']['shortTitle'].append({
                    'url': response.url,
                    'text': titleText,
                    'latency': response.meta.get('download_latency')
                })
        else:
            self.data['crawl']['meta']['multipleTitleTag'].append({
                'url': response.url,
                'text': titleText,
                'latency': response.meta.get('download_latency')
            })
    elif response.status in self.handle_httpstatus_list:
        self.data['crawl']['blockers']['url'].append({
            'url': response.url,
            'code':response.status,
            'text': titleText,
            'latency': response.meta.get('download_latency')
    })

谢谢

Answer 1

你有很多重复的代码，但如果你有这么多不同的可能性，所有这些都很难消除。

一机多用

titleText = response.css('title::text').get()
dataObj = {
    'url': response.url,
    'latency': response.meta.get('download_latency')
}
title = response.css('title').extract()
tagName = 'missingTitle' #default
if response.status == 200:
    if len(title) == 0:
        tagName = 'missingTitle'
    else:
        dataObj['text'] = titleText
    if len(title) > 1:
        tagName = 'multipleTitleTag'
    elif len(title) ==1:
        if len(titleText) > 70:
            tagName = 'longTitle'
        elif len(titleText) < 50:
            tagName = 'shortTitle'
        else:
            #Really nothing done if title between 50 and 70?
            pass
    self.data['crawl']['meta'][tagName].append(dataObj)
    
elif response.status in self.handle_httpstatus_list:
    dataObj['code'] = response.status
    dataObj['text'] = titleText
    self.data['crawl']['meta']['multipleTitleTag'].append(dataObj)

标签名称提取到另一个函数

标题标签功能可以移到辅助函数中，让事情变得更简洁。在那里，标签名称的选择可以很好地结构化，并带有早期回报。总的来说它可能看起来像这样（相应地调整细节）：

def get_tag_name(self, title, titleText):
    if len(title) == 0:
        return 'missingTitle'
    if len(title) > 1:
        return 'multipleTitleTag'
    if len(titleText) > 70:
        return 'longTitle'
    if len(titleText) < 50:
        return 'longTitle'
    return 'DEFAULT' #???

def the_main_one(self, response):
    titleText = response.css('title::text').get()
    dataObj = {
        'url': response.url,
        'latency': response.meta.get('download_latency')
    }
    tagName = 'multipleTitleTag' #default
    title = response.css('title').extract()
    if response.status == 200:
        tagName = self.get_tag_name(title, titleText)
        if len(title) == 0:
            dataObj['text'] = titleText
    elif response.status in self.handle_httpstatus_list:
        dataObj['code'] = response.status
        dataObj['text'] = titleText
    self.data['crawl']['meta'][tagName].append(dataObj) 

它可能不会短很多，但它肯定会消除一些混乱并有助于以后维护代码
如果您在同一级别有很多 IF，您可以考虑不同的方法。现在这似乎是正确的（至少对我而言）。

Answer 2

titleText = response.css('title::text').get()
    metaResponse = {'text':titleText, 'url':response.url, 'httpCode':response.status, 'latency':response.meta.get('download_latency')}

    if response.status == 200:
        if len(response.css('title').extract()) == 0:
            self.data['crawl']['meta']['missingTitle'].append(metaResponse)
        elif len(response.css('title').extract()) == 1:
            if len(titleText) > 70:
                self.data['crawl']['meta']['longTitle'].append(metaResponse)
            elif len(titleText) < 40:
                self.data['crawl']['meta']['shortTitle'].append(metaResponse)
        else:
            self.data['crawl']['meta']['multipleTitleTag'].append(metaResponse)
    elif response.status in self.handle_httpstatus_list:
        self.data['crawl']['blockers']['url'].append(metaResponse)