我要做什么：此网站上有3种食品添加剂列表，我正尝试提取它们以得到3种不同的列表。它们位于<ul>和<li>标签之间的<h2>和<h3>标签中。
我想找到第一个h2，将其下面的所有lis提取到一个列表中，当到达下一个h标签（h3）时，开始一个新列表，并提取其下的所有lis，然后继续进行第三个列表。
我已经尝试过的内容：我已经阅读并发现了一个与我的问题非常相似的问题。 BeautifulSoup: How do I extract all the <li>s from a list of <ul>s that contains some nested <ul>s? 我已尝试应用该答案的逻辑，但对我没有用。
在开始创建列表之前，我正在运行打印语句以查看输出是什么。
import urllib.request as request
import bs4 as bs
sauce = request.urlopen("https://www.foodadditivesworld.com/articles/banned-food-additives.html").read()
soup = bs.BeautifulSoup(sauce, 'lxml')
firstH2 = soup.find('h2') # Start here
# print(firstH2.text)
# print(firstH2.findNextSiblings())
uls = []
for sib in firstH2.findNextSiblings():
# print(child.name)
if sib.name=='h3':
print(sib)
break
elif sib.name == 'div':
print(sib.text)
continue
for c in sib.descendants:
if c.name=='li':
print (c)
正在发生的事情：该代码基本上可以实现我想要的功能，但是它在第一次运行到h3标签时应该中断，但是没有，它会继续到第二个h3标签在停止之前。为什么它没有第一次出现？
答案 0 :(得分：1)
您可以抓取h2和ul标签，然后使用itertools.groupby：
import requests, itertools, re
from bs4 import BeautifulSoup as soup
d = soup(requests.get('https://www.foodadditivesworld.com/articles/banned-food-additives.html').text, 'html.parser')
_, *data = [[i.name, i] for i in d.find_all(re.compile('h2|h3|ul'))]
new_data = [[a, list(b)] for a, b in itertools.groupby(data, key=lambda x:x[0] == 'h2' or x[0] == 'h3')]
new_result = [[new_data[i][-1][0][-1].text, [c.text for b in new_data[i+1][-1] for c in b[-1].find_all('li')]] for i in range(0, len(new_data), 2)]
输出：
[['Banned Food Additives in US', ['Calamus extract', 'Calamus oil', 'Calcium cyclamate', 'Chlorofluorocarbons', 'cinnamyl anthranilate', 'Cobaltous chloride', 'Cobalt sulfate', 'Coumarin', 'Cyclamate', 'Diethyl pyrocarbonatec', 'Dulcin', 'Fd&c green no. 1', 'Fd&c green no. 2', 'Fd&c red no. 3, aluminum lake', 'CFd&c red no. 3, calcium lake', 'Fd&c red no. 1', 'Fd&c red no. 2', 'Fd&c red no. 4', 'Fd&c violet no. 1', 'Magnesium cyclamate', 'Nordihydroguaiaretic acid', 'Potassium cyclamate', 'P-4000', 'Safrole', 'Sodium cyclamate', 'Thiourea']], ['UK Food Additives Banned in Australia and New Zealand', ['E131 Patent Blue V', 'E154 Brown FK', 'E161g Canthaxanthin', 'E180 Litholrubine BK']], ['Preservatives', ['E214 Â\xa0 Ethyl p-hydroxybenzoate', 'E215 Â\xa0 Sodium ethyl p-hydroxybenzoate', 'E219 Â\xa0 Sodium methyl p-hydroxybenzoate', 'E226 Â\xa0 Calcium sulphite', 'E227 Â\xa0 Calcium hydrogen sulphite', 'E230 Â\xa0 Biphenyl; diphenyl', 'E231 Â\xa0 Orthophenyl phenol', 'E232 Â\xa0 Sodium orthophenyl phenol', 'E239 Â\xa0 Hexamethylene tetramine', 'E284 Â\xa0 Boric acid', 'E285 Â\xa0 Sodium tetraborate; borax', 'E356 Â\xa0 Sodium adipate antioxidant']], ['Stabilisers, Thickeners and Gelling Agents Emulsifiers', ['E417 Â\xa0 Tara gum', 'E425 Â\xa0 Konjac', 'E426 Â\xa0 Soybean hemicellulose', 'E226 Â\xa0 Calcium sulphite', 'E432 Polyoxyethylene sorbitan monolaurate; Polysorbate 20', 'E434 Polyoxyethylene sorbitan monopalmitate; Polysorbate 40', 'E459 Â\xa0 Beta-cyclodextrin', 'E462 Â\xa0 Ethyl cellulose', 'E468 Â\xa0 Crosslinked sodium carboxy methyl cellulose', 'E472d Â\xa0 Tartaric acid esters of mono- and diglycerides of fatty acids', 'E474 Â\xa0 Sucroglycerides', 'E483 Â\xa0 Stearyl tartrate', 'E493 Â\xa0 Sorbitan monolaurate', 'E494 Â\xa0 Sorbitan monooleate', 'E495 Â\xa0 Sorbitan monopalmitate', 'E513 Â\xa0 Sulphuric acid', 'E517 Â\xa0 Ammonium sulphate', 'E520 Â\xa0 Aluminium sulphate', 'E521 Â\xa0 Aluminium sodium sulphate', 'E522 Â\xa0 Aluminium potassium sulphate', 'E523 Â\xa0 Aluminium ammonium sulphate', 'E524 Â\xa0 Sodium hydroxide', 'E525 Â\xa0 Potassium hydroxide', 'E527 Â\xa0 Ammonium hydroxide', 'E528 Â\xa0 Magnesium hydroxide', 'E538 Â\xa0 Calcium ferrocyanide', 'E553a Â\xa0 (i) Magnesium silicate', 'E553b Â\xa0 Talc E574 Â\xa0 Gluconic acid', 'E576 Â\xa0 Sodium gluconate', 'E585 Â\xa0 Ferrous lactate', 'E626 Â\xa0 Guanylic acid', 'E628 Â\xa0 Dipotassium guanylate', 'E629 Â\xa0 Calcium guanylate', 'E630 Â\xa0 lnosinic acid', 'E632 Â\xa0 Dipotassium inosinate', 'E633 Â\xa0 Calcium inosinate', "E634 Â\xa0 Calcium 5'-ribonucleotides", 'E650 Â\xa0 Zinc acetate', 'E900 Â\xa0 Dimethylpolysiloxane', 'E902 Â\xa0 Candelilla wax', 'E905 Â\xa0 Microcrystalline wax', 'E912 Â\xa0 Montan acid esters', 'E927b Â\xa0 Carbamide', 'E938 Â\xa0 Argon', 'E939 Â\xa0 Helium', 'E948 Â\xa0 Oxygen', 'E949 Â\xa0 Hydrogen', 'E959 Â\xa0 Neohesperidine DC', 'E962 Â\xa0 Salt of aspartame-acesulfame', 'E999 Â\xa0 Quillaia extract', 'E1103 Â\xa0 Invertase', 'E1202 Â\xa0 Polyvinylpolypyrrolidone', 'E1204 Â\xa0 Pullulan', 'E1451 Â\xa0 Acetylated oxidised starch', 'E1452 Â\xa0 Starch aluminium Octenyl succinate', 'Annatto ExtractM', 'Anthocyanins', 'Lake Allura Red', 'Lake Amaranth', 'Solvent Black 5', 'Solvent Black 7', 'Pigment Fast Yellow G', 'Pigment Green B', 'FD&C; Blue No.2 ', 'FD&C; Blue No.1 ', 'Beverages ', 'Confectionery ', 'Anticaking Agents ', 'Color Retention Agents ']]]
打印结果：
print('\n\n'.join(' {}\n{}'.format(a, '\n'.join(f'\t-{i}' for i in b)) for a, b in new_result))
输出：
Banned Food Additives in US
-Calamus extract
-Calamus oil
-Calcium cyclamate
-Chlorofluorocarbons
-cinnamyl anthranilate
-Cobaltous chloride
-Cobalt sulfate
-Coumarin
-Cyclamate
-Diethyl pyrocarbonatec
-Dulcin
-Fd&c green no. 1
-Fd&c green no. 2
-Fd&c red no. 3, aluminum lake
-CFd&c red no. 3, calcium lake
-Fd&c red no. 1
-Fd&c red no. 2
-Fd&c red no. 4
-Fd&c violet no. 1
-Magnesium cyclamate
-Nordihydroguaiaretic acid
-Potassium cyclamate
-P-4000
-Safrole
-Sodium cyclamate
-Thiourea
UK Food Additives Banned in Australia and New Zealand
-E131 Patent Blue V
-E154 Brown FK
-E161g Canthaxanthin
-E180 Litholrubine BK
Preservatives
-E214 Â Ethyl p-hydroxybenzoate
-E215 Â Sodium ethyl p-hydroxybenzoate
-E219 Â Sodium methyl p-hydroxybenzoate
-E226 Â Calcium sulphite
-E227 Â Calcium hydrogen sulphite
-E230 Â Biphenyl; diphenyl
-E231 Â Orthophenyl phenol
-E232 Â Sodium orthophenyl phenol
-E239 Â Hexamethylene tetramine
-E284 Â Boric acid
-E285 Â Sodium tetraborate; borax
-E356 Â Sodium adipate antioxidant
Stabilisers, Thickeners and Gelling Agents Emulsifiers
-E417 Â Tara gum
-E425 Â Konjac
-E426 Â Soybean hemicellulose
-E226 Â Calcium sulphite
-E432 Polyoxyethylene sorbitan monolaurate; Polysorbate 20
-E434 Polyoxyethylene sorbitan monopalmitate; Polysorbate 40
-E459 Â Beta-cyclodextrin
-E462 Â Ethyl cellulose
-E468 Â Crosslinked sodium carboxy methyl cellulose
-E472d  Tartaric acid esters of mono- and diglycerides of fatty acids
-E474 Â Sucroglycerides
-E483 Â Stearyl tartrate
-E493 Â Sorbitan monolaurate
-E494 Â Sorbitan monooleate
-E495 Â Sorbitan monopalmitate
-E513 Â Sulphuric acid
-E517 Â Ammonium sulphate
-E520 Â Aluminium sulphate
-E521 Â Aluminium sodium sulphate
-E522 Â Aluminium potassium sulphate
-E523 Â Aluminium ammonium sulphate
-E524 Â Sodium hydroxide
-E525 Â Potassium hydroxide
-E527 Â Ammonium hydroxide
-E528 Â Magnesium hydroxide
-E538 Â Calcium ferrocyanide
-E553a  (i) Magnesium silicate
-E553b  Talc E574  Gluconic acid
-E576 Â Sodium gluconate
-E585 Â Ferrous lactate
-E626 Â Guanylic acid
-E628 Â Dipotassium guanylate
-E629 Â Calcium guanylate
-E630 Â lnosinic acid
-E632 Â Dipotassium inosinate
-E633 Â Calcium inosinate
-E634 Â Calcium 5'-ribonucleotides
-E650 Â Zinc acetate
-E900 Â Dimethylpolysiloxane
-E902 Â Candelilla wax
-E905 Â Microcrystalline wax
-E912 Â Montan acid esters
-E927b  Carbamide
-E938 Â Argon
-E939 Â Helium
-E948 Â Oxygen
-E949 Â Hydrogen
-E959 Â Neohesperidine DC
-E962 Â Salt of aspartame-acesulfame
-E999 Â Quillaia extract
-E1103 Â Invertase
-E1202 Â Polyvinylpolypyrrolidone
-E1204 Â Pullulan
-E1451 Â Acetylated oxidised starch
-E1452 Â Starch aluminium Octenyl succinate
-Annatto ExtractM
-Anthocyanins
-Lake Allura Red
-Lake Amaranth
-Solvent Black 5
-Solvent Black 7
-Pigment Fast Yellow G
-Pigment Green B
-FD&C; Blue No.2
-FD&C; Blue No.1
-Beverages
-Confectionery
-Anticaking Agents
-Color Retention Agents