Read files (Edexcel GCSE Computer Science): Revision Notes

Read files

Why do we need to read files?

When working with programmes, we often need to use data that's stored outside our programme. This data might be saved in files on your computer's hard drive, a USB stick, or other storage devices. Before your programme can work with this data, it must first read the data into memory. Think of it like taking information from a filing cabinet and putting it on your desk so you can work with it.

Understanding text files

The text files you'll work with in your GCSE exam follow a specific format that makes them easy to process. Here's what you need to know:

File structure

• Each record (like information about one item) is stored on a separate line
• Within each record, different pieces of information called fields are separated by commas
• This format is called CSV (Comma Separated Values)

For example, a file containing prize information might look like this:

Teddy Bear,2215,4.25
Goldfish,2977,1.07
Inflatable Hammer,1785,1.49
Jumbo Sunglasses,1931,3.18

Notice there are no spaces after the commas, and there's no comma after the last field in each record.

Hidden characters

Although you can't see them when looking at a text file, there are special invisible characters called carriage return and line feed at the end of each line. These tell the computer where one line ends and the next begins. When processing files, you'll need to remove these characters to work with clean data.

Reading a file step by step

Here's how to read and process a text file in Python:

Let's break down this code to understand what each part does:

Opening the file

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

This opens your file in read mode (the "r" means read-only). Think of this like opening a book to start reading it.

Processing each line

for line in file:

This creates a loop that goes through the file one line at a time. It's like reading a book page by page.

Cleaning the data

line = line.strip()

The strip() function removes those invisible carriage return and line feed characters from the end of each line. This gives you clean data to work with.

Splitting into fields

fields = line.split(",")

The split() function breaks the line apart wherever it finds a comma, creating a list of separate pieces of information. For example, "Teddy Bear,2215,4.25" becomes ["Teddy Bear", "2215", "4.25"].

Converting data types

This is a crucial step that many students miss in exams! When you read from a text file, everything comes in as a string (text), even numbers. You need to convert them to the right data type:

prize.append(fields[0])        # Keep as string for the name
prize.append(int(fields[1]))   # Convert to integer for whole numbers
prize.append(float(fields[2])) # Convert to decimal for prices

Storing the data

prizeTable.append(prize)

This adds each complete record to your main data structure, building up a two-dimensional list (a list of lists).

Closing the file

file.close()

Always remember to close your files when finished! This is like putting a book back on the shelf when you're done reading it.

Common exam mistakes to avoid

Real-world applications