Write files (Edexcel GCSE Computer Science): Revision Notes

Writing files

Why do we need to write files?

When you're running a programme, all the data exists only in the computer's memory (RAM). This means that as soon as your programme finishes running, all that data disappears forever! This is a problem if you want to keep important information for later use.

To solve this problem, we need to save our data to a file on a storage device like a hard drive or USB stick. This process is called writing to a file, and it allows our data to persist even after the programme ends.

Understanding text file formats

In your GCSE exam, you'll work with text files that have a specific structure. These files are organised using:

• Records: Each record contains information about one item (like one prize or one car)
• Fields: Each piece of information within a record (like name, number, price)
• Separators: Commas separate the fields within each record
• Lines: Each record appears on its own separate line

For example, a text file might look like this:

Teddy Bear,2215,4.25
Goldfish,2977,1.07
Inflatable Hammer,1785,1.49

The importance of line feed characters

When writing to files, you need to add a special character called a line feed (written as \n in code) at the end of each line. Without this character, all your text would appear on one extremely long line, making it impossible to read properly in a text editor.

How to write data to a file

Writing data to a file involves several important steps that you must follow in the correct order:

Step 1: Open the file in write mode

First, you need to tell the computer which file you want to write to and how you want to use it. In Python, you use the open() function with write mode (indicated by "w"):

file = open("Prizes.txt", "w")

Step 2: Process your data structure

Most likely, your data will be stored in an internal data structure like an array or list. You'll need to loop through this structure to access each record one at a time:

for prize in prizeTable:

Step 3: Build each line of text

For each record, you need to convert all the fields to strings and combine them with commas. This process is called string concatenation:

outline = str(prize[0]) + ","
outline = outline + str(prize[1]) + ","
outline = outline + str(prize[2])

Step 4: Add the line feed character

Don't forget to add \n at the end of each line to ensure proper formatting:

outline = outline + "\n"

Step 5: Write the line to the file

Use the write() method to actually save the line to your file:

file.write(outline)

Step 6: Close the file

Always remember to close the file when you're finished. This is crucial because it ensures all your data is properly saved and frees up computer resources:

file.close()

Putting it all together

Here's how all these steps work together in a complete example. The programme takes data from an array called prizeTable and writes it to a text file called "Prizes.txt". Each prize has three pieces of information: name, number, and price.

Practice example