59 — Editor — a tiny text editor

A text file is one long string. An editor works on a buffer — the same text split into a list of lines, one per row. You add, remove, and list those rows, then save writes the whole buffer back to the file.

#Steps

1. "\n".join(lines) merges lines into one text with newlines between them; .splitlines() is the exact opposite. It prints Hello, World!, then ['Hello', 'World!']:

   lines = ["Hello", "World!"]
   text = "\n".join(lines)
   show text
   back = text.splitlines()
   show back
   

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2. The buffer lives in the file between runs. As in guide 13, a saved file becomes a list of lines, and a first run starts empty:

   use file latest
   import os
   
   if os.path.exists("notes.txt"):
       buffer = file_read("notes.txt").splitlines()
   else:
       buffer = []
   

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3. Commands arrive as whole lines. line.split() splits on spaces, parts[0] is the command word, and " ".join(parts[1:]) reconnects the rest — the text for add. It prints add, then Hello world; guide 49 split tokens the same way:

   line = "add Hello world"
   parts = line.split()
   show parts[0]
   show " ".join(parts[1:])
   

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4. remove <n> needs a number. int(parts[1]) turns typed text into an integer, - 1 makes it zero-based, and buffer.pop(i) deletes that row. It prints ['a', 'c'] — line 2 was removed:

   buffer = ["a", "b", "c"]
   n = 2
   i = int(n) - 1
   buffer.pop(i)
   show buffer
   

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5. The whole editor. Save editor.nme:

   # editor.nme — a tiny line-based text editor.
   # Run: nme r editor
   # Type add <text>, list, remove <n>, save, or quit.
   
   use file latest
   import os
   
   # Load the saved buffer, or start with an empty one.
   if os.path.exists("notes.txt"):
       buffer = file_read("notes.txt").splitlines()
   else:
       buffer = []
   
   show "Tiny editor — notes.txt"
   while True:
       show "Commands: add, list, remove, save, quit"
       ask line, "> "
       parts = line.split()
       command = parts[0] if parts else ""
       if command == "add":
           # The text after the command word is the new line.
           text = " ".join(parts[1:])
           buffer.append(text)
           show f"Added line {len(buffer)}"
       elif command == "list":
           show f"{len(buffer)} lines"
           for i in range(len(buffer)):
               show f"{i + 1}: {buffer[i]}"
       elif command == "remove":
           # Remove line N: 1 is the first line.
           i = int(parts[1]) - 1
           if i >= 0 and i < len(buffer):
               buffer.pop(i)
               show "Removed"
           else:
               show "No such line"
       elif command == "save":
           file_write("notes.txt", "\n".join(buffer))
           show "Saved"
       elif command == "quit":
           show "Bye!"
           break
       else:
           show "Unknown command"
   

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   add appends to the list, list walks it with f"{i + 1}:" so line numbers start at 1, and save does the join from step 1 in reverse — "\n".join(buffer) into the file.

6. Run it and feed the commands through a pipe. add Hello and add World! fill the buffer, remove 1 deletes Hello, and save keeps World!:

   printf 'add Hello\nadd World!\nlist\nremove 1\nlist\nsave\nquit\n' | nme r editor
   

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   Tiny editor — notes.txt
   Commands: add, list, remove, save, quit
   > Added line 1
   Commands: add, list, remove, save, quit
   > Added line 2
   Commands: add, list, remove, save, quit
   > 2 lines
   1: Hello
   2: World!
   Commands: add, list, remove, save, quit
   > Removed
   Commands: add, list, remove, save, quit
   > 1 lines
   1: World!
   Commands: add, list, remove, save, quit
   > Saved
   Commands: add, list, remove, save, quit
   > Bye!
   

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   cat notes.txt shows the saved buffer — a single World! line. Run the editor again and list loads that line back, so the file and the buffer stay in sync across sessions.

#Try it yourself

Add an upper command that uppercases the whole buffer before saving ([l.upper() for l in buffer]), or a clear command that empties the list. Make save print how many lines it wrote.

#What you learned

• A buffer is a list of lines; "\n".join(buffer) saves it and .splitlines() loads it.
• line.split() separates a command word from its text; " ".join(parts[1:]) reconnects the text.
• int(...) - 1 turns a typed line number into a list index; buffer.pop(i) removes a row.
• save writes the file, so the buffer survives between runs.