import os
def get_txt():
  """使用原始打开io方式打开"""
  with open('demo.txt', 'r', encoding='utf-8') as f:
    return f.read()

def get_demo_txt():
  """修改获取路径方式，使用io打开"""
  current_dir = os.path.dirname(__file__)
  file_path = os.path.join(current_dir, 'demo.txt')
  with open(file_path, 'r', encoding='utf-8') as f:
    return f.read()
if __name__ == "__main__":
  """类内测试，均无异常"""
  print("get_demo_txt() :", get_demo_txt())
  # get_demo_txt() : The text is from demo.txt.

  print("get_txt() :", get_txt())
  # get_txt() : The text is from demo.txt.

$ python demo/demo.py
get_demo_txt() : The text is from demo.txt.
Traceback (most recent call last):
 File "demo/demo.py", line 21, in <module>
  print("get_txt() :", get_txt()) # get_txt() : The text is from demo.txt.
 File "demo/demo.py", line 6, in get_txt
  with open('demo.txt', 'r', encoding='utf-8') as f:
FileNotFoundError: [Errno 2] No such file or directory: 'demo.txt'

from setuptools import find_packages, setup

setup(
  name='demo',
  version='1.0.0',
  packages=find_packages(),
  zip_sage=False,
)

$ python setup.py sdist

setup.py
demo/__init__.py
demo/demo.py
demo.egg-info/PKG-INFO
demo.egg-info/SOURCES.txt
demo.egg-info/dependency_links.txt
demo.egg-info/top_level.txt

from setuptools import find_packages, setup

setup(
  name='demo',
  version='1.0.0',
  packages=find_packages(),
  zip_sage=False,
  include_package_data=True, # 打包包含静态文件标识
)

include demo/demo.txt

$ python setup.py sdist

MANIFEST.in
setup.py
demo/__init__.py
demo/demo.py
demo/demo.txt
demo.egg-info/PKG-INFO
demo.egg-info/SOURCES.txt
demo.egg-info/dependency_links.txt
demo.egg-info/top_level.txt