scrapy爬虫:scrapy.FormRequest中formdata参数详解
1. 背景
在网页爬取的时候,有时候会使用scrapy.FormRequest向目标网站提交数据(表单提交)。参照scrapy官方文档的标准写法是:
# header信息 unicornHeader = { 'Host': 'www.example.com', 'Referer': 'http://www.example.com/', } # 表单需要提交的数据 myFormData = {'name': 'John Doe', 'age': '27'} # 自定义信息,向下层响应(response)传递下去 customerData = {'key1': 'value1', 'key2': 'value2'} yield scrapy.FormRequest(url = "http://www.example.com/post/action", headers = unicornHeader, method = 'POST', # GET or POST formdata = myFormData, # 表单提交的数据 meta = customerData, # 自定义,向response传递数据 callback = self.after_post, errback = self.error_handle, # 如果需要多次提交表单,且url一样,那么就必须加此参数dont_filter,防止被当成重复网页过滤掉了 dont_filter = True )
但是,当表单提交数据myFormData 是形如字典内嵌字典的形式,又该如何写?
2. 案例 — 参数为字典
在做亚马逊网站爬取时,当进入商家店铺,爬取店铺内商品列表时,发现采取的方式是ajax请求,返回的是json数据。
请求信息如下:
响应信息如下:
如上图所示,From Data中的数据包含一个字典:
marketplaceID:ATVPDKIKX0DER seller:A2FE6D62A4WM6Q productSearchRequestData:{"marketplace":"ATVPDKIKX0DER","seller":"A2FE6D62A4WM6Q","url":"/sp/ajax/products","pageSize":12,"searchKeyword":"","extraRestrictions":{},"pageNumber":"1"} # formDate 必须构造如下: myFormData = { 'marketplaceID' : 'ATVPDKIKX0DER', 'seller' : 'A2FE6D62A4WM6Q', # 注意下面这一行,内部字典是作为一个字符串的形式 'productSearchRequestData' :'{"marketplace":"ATVPDKIKX0DER","seller":"A2FE6D62A4WM6Q","url":"/sp/ajax/products","pageSize":12,"searchKeyword":"","extraRestrictions":{},"pageNumber":"1"}' }
在amazon中实际使用的构造方法如下:
def sendRequestForProducts(response): ajaxParam = response.meta for pageIdx in range(1, ajaxParam['totalPageNum']+1): ajaxParam['isFirstAjax'] = False ajaxParam['pageNumber'] = pageIdx unicornHeader = { 'Host': 'www.amazon.com', 'Origin': 'https://www.amazon.com', 'Referer': ajaxParam['referUrl'], } ''' marketplaceID:ATVPDKIKX0DER seller:AYZQAQRQKEXRP productSearchRequestData:{"marketplace":"ATVPDKIKX0DER","seller":"AYZQAQRQKEXRP","url":"/sp/ajax/products","pageSize":12,"searchKeyword":"","extraRestrictions":{},"pageNumber":1} ''' productSearchRequestData = '{"marketplace": "ATVPDKIKX0DER", "seller": "' + f'{ajaxParam["sellerID"]}' + '","url": "/sp/ajax/products", "pageSize": 12, "searchKeyword": "","extraRestrictions": {}, "pageNumber": "' + str(pageIdx) + '"}' formdataProduct = { 'marketplaceID': ajaxParam['marketplaceID'], 'seller': ajaxParam['sellerID'], 'productSearchRequestData': productSearchRequestData } productAjaxMeta = ajaxParam # 请求店铺商品列表 yield scrapy.FormRequest( url = 'https://www.amazon.com/sp/ajax/products', headers = unicornHeader, formdata = formdataProduct, func = 'POST', meta = productAjaxMeta, callback = self.solderProductAjax, errback = self.error, # 处理http error dont_filter = True, # 需要加此参数的 )
3. 原理分析
举例来说,目前有如下一笔数据:
formdata = { 'Field': {"pageIdx":99, "size":"10"}, 'func': 'nextPage', }
从网页上,可以看到请求数据如下:
Field=%7B%22pageIdx%22%3A99%2C%22size%22%3A%2210%22%7D&func=nextPage
第一种,按照如下方式发出请求,结果如下(正确):
yield scrapy.FormRequest( url = 'https://www.example.com/sp/ajax', headers = unicornHeader, formdata = { 'Field': '{"pageIdx":99, "size":"10"}', 'func': 'nextPage', }, func = 'POST', callback = self.handleFunc, ) # 请求数据为:Field=%7B%22pageIdx%22%3A99%2C%22size%22%3A%2210%22%7D&func=nextPage
第二种,按照如下方式发出请求,结果如下(错误,无法获取到正确的数据):
yield scrapy.FormRequest( url = 'https://www.example.com/sp/ajax', headers = unicornHeader, formdata = { 'Field': {"pageIdx":99, "size":"10"}, 'func': 'nextPage', }, func = 'POST', callback = self.handleFunc, ) # 经过错误的编码之后,发送的请求为:Field=size&Field=pageIdx&func=nextPage
我们跟踪看一下scrapy中的源码:
# E:/Miniconda/Lib/site-packages/scrapy/http/request/form.py # FormRequest class FormRequest(Request): def __init__(self, *args, **kwargs): formdata = kwargs.pop('formdata', None) if formdata and kwargs.get('func') is None: kwargs['func'] = 'POST' super(FormRequest, self).__init__(*args, **kwargs) if formdata: items = formdata.items() if isinstance(formdata, dict) else formdata querystr = _urlencode(items, self.encoding) if self.func == 'POST': self.headers.setdefault(b'Content-Type', b'application/x-www-form-urlencoded') self._set_body(querystr) else: self._set_url(self.url + ('&' if '?' in self.url else '?') + querystr) # 关键函数 _urlencode def _urlencode(seq, enc): values = [(to_bytes(k, enc), to_bytes(v, enc)) for k, vs in seq for v in (vs if is_listlike(vs) else [vs])] return urlencode(values, doseq=1)
分析过程如下:
# 第一步:items = formdata.items() if isinstance(formdata, dict) else formdata # 第一步结果:经过items()方法执行后,原始的dict格式变成如下列表形式: dict_items([('func', 'nextPage'), ('Field', {'size': '10', 'pageIdx': 99})]) # 第二步:再经过后面的 _urlencode方法将items转换成如下: [(b'func', b'nextPage'), (b'Field', b'size'), (b'Field', b'pageIdx')] # 可以看到就是在调用 _urlencode方法的时候出现了问题,上面的方法执行过后,会使字典形式的数据只保留了keys(value是字典的情况下,只保留了value字典中的key).
解决方案: 就是将字典当成普通的字符串,然后编码(转换成bytes),进行传输,到达服务器端之后,服务器会反过来进行解码,得到这个字典字符串。然后服务器按照Dict进行解析。
拓展:对于其他特殊类型的数据,都按照这种方式打包成字符串进行传递。
4. 补充1 ——参数类型
formdata的 参数值 必须是unicode , str 或者 bytes object,不能是整数。
案例:
yield FormRequest( url = 'https://www.amztracker.com/unicorn.php', headers = unicornHeader, # formdata 的参数必须是字符串 formdata={'rank': 10, 'category': productDetailInfo['topCategory']}, method = 'GET', meta = {'productDetailInfo': productDetailInfo}, callback = self.amztrackerSale, errback = self.error, # 本项目中这里触发errback占绝大多数 dont_filter = True, # 按理来说是不需要加此参数的 ) # 提示如下ERROR: Traceback (most recent call last): File "E:\Miniconda\lib\site-packages\scrapy\utils\defer.py", line 102, in iter_errback yield next(it) File "E:\Miniconda\lib\site-packages\scrapy\spidermiddlewares\offsite.py", line 29, in process_spider_output for x in result: File "E:\Miniconda\lib\site-packages\scrapy\spidermiddlewares\referer.py", line 339, in <genexpr> return (_set_referer(r) for r in result or ()) File "E:\Miniconda\lib\site-packages\scrapy\spidermiddlewares\urllength.py", line 37, in <genexpr> return (r for r in result or () if _filter(r)) File "E:\Miniconda\lib\site-packages\scrapy\spidermiddlewares\depth.py", line 58, in <genexpr> return (r for r in result or () if _filter(r)) File "E:\PyCharmCode\categorySelectorAmazon1\categorySelectorAmazon1\spiders\categorySelectorAmazon1Clawer.py", line 224, in parseProductDetail dont_filter = True, File "E:\Miniconda\lib\site-packages\scrapy\http\request\form.py", line 31, in __init__ querystr = _urlencode(items, self.encoding) File "E:\Miniconda\lib\site-packages\scrapy\http\request\form.py", line 66, in _urlencode for k, vs in seq File "E:\Miniconda\lib\site-packages\scrapy\http\request\form.py", line 67, in <listcomp> for v in (vs if is_listlike(vs) else [vs])] File "E:\Miniconda\lib\site-packages\scrapy\utils\python.py", line 117, in to_bytes 'object, got %s' % type(text).__name__) TypeError: to_bytes must receive a unicode, str or bytes object, got int # 正确写法: formdata = {'rank': str(productDetailInfo['topRank']), 'category': productDetailInfo['topCategory']},
原理部分(源代码):
# 第一阶段: 字典分解为items if formdata: items = formdata.items() if isinstance(formdata, dict) else formdata querystr = _urlencode(items, self.encoding) # 第二阶段: 对value,调用 to_bytes 编码 def _urlencode(seq, enc): values = [(to_bytes(k, enc), to_bytes(v, enc)) for k, vs in seq for v in (vs if is_listlike(vs) else [vs])] return urlencode(values, doseq=1) # 第三阶段: 执行 to_bytes ,参数要求是bytes, str def to_bytes(text, encoding=None, errors='strict'): """Return the binary representation of `text`. If `text` is already a bytes object, return it as-is.""" if isinstance(text, bytes): return text if not isinstance(text, six.string_types): raise TypeError('to_bytes must receive a unicode, str or bytes ' 'object, got %s' % type(text).__name__)
5. 补充2 ——参数为中文
formdata的 参数值 必须是unicode , str 或者 bytes object,不能是整数。
以1688网站搜索产品为案例:
搜索信息如下(搜索关键词为:动漫周边):
可以看到 动漫周边 == %B6%AF%C2%FE%D6%DC%B1%DF
# scrapy中这个请求的构造如下 # python3 所有的字符串都是unicode unicornHeaders = { ':authority': 's.1688.com', 'Referer': 'https://www.1688.com/', } # python3 所有的字符串都是unicode # 动漫周边 tobyte为:%B6%AF%C2%FE%D6%DC%B1%DF formatStr = "动漫周边".encode('gbk') print(f"formatStr = {formatStr}") yield FormRequest( url = 'https://s.1688.com/selloffer/offer_search.htm', headers = unicornHeaders, formdata = {'keywords': formatStr, 'n': 'y', 'spm': 'a260k.635.1998096057.d1'}, method = 'GET', meta={}, callback = self.parseCategoryPage, errback = self.error, # 本项目中这里触发errback占绝大多数 dont_filter = True, # 按理来说是不需要加此参数的 ) # 日志如下: formatStr = b'\xb6\xaf\xc2\xfe\xd6\xdc\xb1\xdf' 2017-11-16 15:11:02 [scrapy.downloadermiddlewares.redirect] DEBUG: Redirecting (302) to <GET https://sec.1688.com/query.htm?smApp=searchweb2&smPolicy=searchweb2-selloffer-anti_Spider-seo-html-checklogin&smCharset=GBK&smTag=MTE1LjIxNi4xNjAuNDYsLDU5OWQ1NWIyZTk0NDQ1Y2E5ZDAzODRlOGM1MDI2OTZj&smReturn=https%3A%2F%2Fs.1688.com%2Fselloffer%2Foffer_search.htm%3Fkeywords%3D%25B6%25AF%25C2%25FE%25D6%25DC%25B1%25DF%26n%3Dy%26spm%3Da260k.635.1998096057.d1&smSign=05U0%2BJXfKLQmSbsnce55Yw%3D%3D> from <GET https://s.1688.com/selloffer/offer_search.htm?keywords=%B6%AF%C2%FE%D6%DC%B1%DF&n=y&spm=a260k.635.1998096057.d1> # https://s.1688.com/selloffer/offer_search.htm?keywords=%B6%AF%C2%FE%D6%DC%B1%DF&n=y&spm=a260k.635.1998096057.d1
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