File handling

Assume scores.txt already contains one score per line. A program can open a file, process its contents, then close it. ERL checks endOfFile() before reading each next line. Python can loop over the open file; with open(...) closes it automatically, even if an error occurs.

file = open("scores.txt")
WHILE NOT file.endOfFile()
    line = file.readLine()
    OUTPUT line
ENDWHILE
file.close()

with open("scores.txt", "r", encoding="utf-8") as file:
    for line in file:
        print(line.rstrip())

Both examples read line by line. ERL needs an explicit close; Python's with manages closing for you.

Open a file for writing, write each line, then close it. ERL uses writeLine; Python's write() does not add a new line automatically, so include \n when needed. Opening with Python mode "w" replaces existing contents. with closes the file at the end of its indented block.

file = open("scores.txt", "w")
file.writeLine("Ada,18")
file.close()

with open("scores.txt", "w", encoding="utf-8") as file:
    file.write("Ada,18\n")

A program's variables are held in RAM, so their values are lost when the program ends. A file is saved on secondary storage, so its data is kept between runs. A game can save its high scores, an app can remember a user's settings, and a program can work through a list of records that someone else has saved.

A program usually reads a file when it starts, then writes it back when the data changes. Every file operation follows the same order: open the file, read or write, then close it.

In ERL, newFile() creates a new, empty file. The program then opens it, writes to it and closes it. In Python, opening a file in mode "w" creates it if it doesn't exist.

newFile("log.txt")
log = open("log.txt")
log.writeLine("Started")
log.close()

with open("log.txt", "w", encoding="utf-8") as log:
    log.write("Started\n")

To add a line to the end of a file without losing what is already there, Python opens it in mode "a" (append). Mode "w" would replace the whole file.