scrapy爬虫:scrapy.FormRequest中formdata参数详解
作者：Kosmoo
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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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