Python爬虫：循环多次输出列表，仅需最终完整列表的问题

原代码 #

from urllib.request import urlopen
from bs4 import BeautifulSoup

url = 'http://wholepeople.com/best-thrift-stores-in-nyc/#:~:text=1%20Beacon%27s%20Closet.%20We%20think%20any%20thrifter%20in,...%2010%20Emma%20Rogue.%20...%20More%20items...%20'
page = urlopen(url)
soup = BeautifulSoup(page, 'html.parser')
h2Tags = soup.find_all('h2')
# 原代码缺少列表初始化，会触发NameError
storeList = []
for store in h2Tags[:12]:
    allStores = (store.text)
    storeList.append(allStores)
    print(storeList)

当前输出 #

['Beacon’s Closet']
['Beacon’s Closet', 'Laced Up']
['Beacon’s Closet', 'Laced Up', '2ND Street']
['Beacon’s Closet', 'Laced Up', '2ND Street', 'Buffalo Exchange']
['Beacon’s Closet', 'Laced Up', '2ND Street', 'Buffalo Exchange', 'Tired Thrift']
['Beacon’s Closet', 'Laced Up', '2ND Street', 'Buffalo Exchange', 'Tired Thrift', 'L Train Vintage']
['Beacon’s Closet', 'Laced Up', '2ND Street', 'Buffalo Exchange', 'Tired Thrift', 'L Train Vintage', 'Cure Thrift Shop']
['Beacon’s Closet', 'Laced Up', '2ND Street', 'Buffalo Exchange', 'Tired Thrift', 'L Train Vintage', 'Cure Thrift Shop', 'Crossroads Trading']
['Beacon’s Closet', 'Laced Up', '2ND Street', 'Buffalo Exchange', 'Tired Thrift', 'L Train Vintage', 'Cure Thrift Shop', 'Crossroads Trading', 'The Attic']
['Beacon’s Closet', 'Laced Up', '2ND Street', 'Buffalo Exchange', 'Tired Thrift', 'L Train Vintage', 'Cure Thrift Shop', 'Crossroads Trading', 'The Attic', 'Emma Rogue']
['Beacon’s Closet', 'Laced Up', '2ND Street', 'Buffalo Exchange', 'Tired Thrift', 'L Train Vintage', 'Cure Thrift Shop', 'Crossroads Trading', 'The Attic', 'Emma Rogue', 'Flamingo’s Vintage Pound']
['Beacon’s Closet', 'Laced Up', '2ND Street', 'Buffalo Exchange', 'Tired Thrift', 'L Train Vintage', 'Cure Thrift Shop', 'Crossroads Trading', 'The Attic', 'Emma Rogue', 'Flamingo’s Vintage Pound', 'Monk Vintage Clothing']

问题原因 #

你把print(storeList)写在了for循环内部，每完成一次循环（往列表里添加一个元素）就会执行一次打印，所以会输出12次逐步增长的列表。

解决方法 #

把print(storeList)移到for循环外面，等所有元素都添加完成后，再打印最终的完整列表。同时补上原代码缺失的storeList = []初始化语句，避免报错。

修改后的代码：

from urllib.request import urlopen
from bs4 import BeautifulSoup

url = 'http://wholepeople.com/best-thrift-stores-in-nyc/#:~:text=1%20Beacon%27s%20Closet.%20We%20think%20any%20thrifter%20in,...%2010%20Emma%20Rogue.%20...%20More%20items...%20'
page = urlopen(url)
soup = BeautifulSoup(page, 'html.parser')
h2Tags = soup.find_all('h2')
storeList = []
for store in h2Tags[:12]:
    allStores = store.text
    storeList.append(allStores)
# 循环结束后打印完整列表
print(storeList)

运行后只会输出最终的完整列表：

['Beacon’s Closet', 'Laced Up', '2ND Street', 'Buffalo Exchange', 'Tired Thrift', 'L Train Vintage', 'Cure Thrift Shop', 'Crossroads Trading', 'The Attic', 'Emma Rogue', 'Flamingo’s Vintage Pound', 'Monk Vintage Clothing']

内容的提问来源于stack exchange，提问作者arosesthorn