Text files

Files keep data

• Variables vanish when a program ends; a file stores data so it lasts.
• The exam covers reading from and writing to text files.
• Work in three steps: open, read or write, then close.

Writing to a file

• open(name, "w") opens a file for writing ("w" overwrites what was there).
• with closes the file automatically when the block ends.
• \n starts a new line in the file.

with open("notes.txt", "w") as f:
    f.write("Hello\n")
    f.write("World\n")

Reading a file

• open(name, "r") opens a file for reading.
• .read() pulls in the whole contents as one string.

with open("notes.txt", "r") as f:
    text = f.read()
print(text)

Reading line by line

• Looping over the file gives one line at a time — handy for totalling or counting.

with open("notes.txt", "r") as f:
    for line in f:
        print(line.strip())

In the exam: file handling

• Pseudocode opens a file for a mode, reads or writes, then closes it.

OPENFILE "notes.txt" FOR WRITE
WRITEFILE "notes.txt", "Hello"
CLOSEFILE "notes.txt"

Common mistakes

• Open, then read or write, then close the file.
• A line you read still carries its newline character.

Now you try

• Write a file, then open it again to read it back.
• Press Check answer to test your code.