How to reuse result of looping through and filtering file names instead of filtering again each time?

Question

This script generates a table of contents .md file for VS Code extension "Notes" (Dion Munk) users and works as intended.

However, get_body() is highly inefficient, in that it re-scans all files for every key in the cats (categories) dictionary.

How can I loop through files only once and still achieve desired result?

_toc.py

"""
Python script to generate a table of contents .md file for VSCode "Notes" users
Run script in Notes.notesLocation to generate, then open _toc.md in preview mode
User must prefix note file names with corresponding values in cats (categories)
    i.e. dj_admin_model.md, py_polymorphism.md, st_ascii.md 
User could put a top link in every note to quickly return to table of contents
    e.g. [< content](_toc.md)
"""
import os

dbug = True
path = '.'
ftyp = '.md'
file = '_toc.md'
cats = {
   'Config'    : '_',
   'Django'    : 'dj_',
   'Markdown'  : 'md_',
   'Python'    : 'py_',
   'Standard'  : 'st_',
   'VSCode'    : 'vs_',
}

def get_files():
    for _, _, files in os.walk(path):
        return (f for f in files if f.lower().endswith(ftyp.lower()))

def get_body():
   body = 
      f'["{file}" generated by running "{__file__}".]: #nn# Contentnn'

   for key, val in cats.items():
      body += f'### {key}n'
      # relooping files for each key in cats inefficient - TODO
      for f in get_files():
         if f.startswith(val):
            body += 
               f"- [{f.replace('.md', '').split('_', 1)[1]}]({f})n"
      body += 'n'
   return body

def write_toc():
   with open(file, mode='wt') as f:
      f.write(get_body())

def print_toc():
   with open(file) as f:
      print(f.read())

def main():
   write_toc()
   if dbug:
      print('_'*60)
      print_toc()

if __name__ == '__main__':
   main()

_toc.md (example desired output)

["_toc.md" generated by running "_toc.py".]: #

# Content

### Config
- [toc](_toc.md)

### Django
- [admin_model](dj_admin_model.md)

### Markdown
- [syntax](md_syntax.md)

### Python
- [file_stream](py_file_stream.md)
- [operators](py_operators.md)
- [pip](py_pip.md)
- [polymorphism](py_polymorphism.md)
- [venv](py_venv.md)

### Standard
- [ascii](st_ascii.md)

### VSCode
- [keyboard](vs_keyboard.md)

_toc.md (mock preview)

Content

Django

admin_model

Markdown

syntax

Python

Standard

ascii

VSCode

keyboard

Asked By: Mlek D. Nairb

||

Source

Answer 1

f_list solution by Jarvis – get_files() now only called once!

Revised get_body():

def get_body():
   f_list = list(get_files())
   body = 
      f'["{file}" generated by running "{__file__}".]: #nn# Contentnn'

   for key, val in cats.items():
      body += f'### {key}n'
      for f in f_list:
         if f.startswith(val):
            body += 
               f"- [{f.replace('.md', '').split('_', 1)[1]}]({f})n"
      body += 'n'
   return body

Answered By: mkrieger1