Python Re：测试过的正则表达式模式不返回匹配项

使用下面的python我试图找到带有markdown文件的特定标题

import re

source_file = open('readme.md')

#Defines variables containing the headings as Regex searches

product_name = re.compile('(?mi)^#+[^\S\n]product.*name')
product_version = re.compile('(?mi)^#+[^\S\n]product.*version')
product_description = re.compile('(?mi)^#+[^\S\n]product.*description')

#Adds the required headings to a list
headings = [product_name, product_version, product_description]

#Opens the readme, searches for the specified headings, then uses print_section to print the content under the headings
with open('readme.md') as file:
    for x in headings:
        content = x.search(file.read()).group(0)
        print(content)

readme.md文件包含以下占位符文本

# Product Name
Test Product
## Product Version
0.01
## Product Description
A short overview of what this product is; what it does; and what its intended use case is
# Specifications
## Networking
the quick brown fox jumped over the lazy dog
## Data Usage
This is line one of the sample
This is line two of the sample

我从运行此文件得到的响应是：

# Product Name
Traceback (most recent call last):
  File "sample.py", line 16, in <module>
    content = x.search(file.read()).group(0)
AttributeError: 'NoneType' object has no attribute 'group'

所以我认为第二个和第三个Regex模式存在问题。但是在正则表达式测试器中，它们似乎可以正确匹配。我无法真正发现这些模式与第一个成功的模式之间的任何区别，甚至尝试交换markdown文件中内容的顺序，但仍然只有product_name匹配。