要使用BeautifulSoup按id取消注释，可以按照以下步骤操作：

1. 导入必要的库：

from bs4 import BeautifulSoup

2. 创建BeautifulSoup对象并加载HTML内容：

html = """






This is a paragraph.


"""

soup = BeautifulSoup(html, 'html.parser')

3. 使用find方法找到指定id的标签：

paragraph_tag = soup.find(id='paragraph')

4. 取消注释：

if paragraph_tag:
    comments = paragraph_tag.find_all(text=lambda text: isinstance(text, Comment))
    for comment in comments:
        comment.extract()

完整的代码示例如下：

from bs4 import BeautifulSoup
from bs4.element import Comment

html = """






This is a paragraph.


"""

soup = BeautifulSoup(html, 'html.parser')
paragraph_tag = soup.find(id='paragraph')

if paragraph_tag:
    comments = paragraph_tag.find_all(text=lambda text: isinstance(text, Comment))
    for comment in comments:
        comment.extract()

print(soup.prettify())

运行以上代码，将会打印出取消注释后的HTML内容：

 
  
 
 
  

   This is a paragraph.