How Do You Open, Read, Write, and Close a File in Python or Java?

Use Python's open() function or Java's file-stream classes to access a file, then read from or write to it before closing it. A Python context manager or Java try-with-resources statement is preferred because it closes the file automatically.

The File-Processing Mechanism

In file processing, a program normally follows four steps: open the file, process its contents, write data if required, and close the file. Closing releases the operating system resource and ensures buffered output is saved.

Python Example

with open("data.txt", "r") as input_file:
    contents = input_file.read()

with open("output.txt", "w") as output_file:
    output_file.write(contents)

The mode "r" means read, while "w" means write and replaces existing contents. The mode "a" means append, adding data at the end. Without with, the programmer must call input_file.close() or output_file.close() explicitly.

Java Example

try (BufferedReader reader = new BufferedReader(
        new FileReader("data.txt"));
     BufferedWriter writer = new BufferedWriter(
        new FileWriter("output.txt"))) {

    String line;
    while ((line = reader.readLine()) != null) {
        writer.write(line);
        writer.newLine();
    }
} catch (IOException e) {
    System.out.println("File error");
}

Here, null indicates the end of file. IOException handles problems such as a missing file or failed write operation.

IB Exam Technique

For B2.5 File processing, trace the sequence open, read/write, close and identify the file mode. A common misconception is that writing automatically preserves existing data: write mode usually overwrites it, whereas append mode preserves it and adds new data.