Text files: open, read, write, append and close

Opening and closing (spec 8.2.3)

open(filename, mode) returns a file object. Modes: "r" read (the file must exist), "w" write (creates the file or erases an existing one), "a" append (adds to the end). Always close() the file so the data is saved and the file is released.

f = open("scores.txt", "w")
f.write("Ana,72\n")
f.write("Ben,64\n")
f.close()
f = open("scores.txt", "a")
f.writelines(["Cai,81\n", "Dee,59\n"])
f.close()
f = open("scores.txt", "r")
print(f.read())
f.close()

Output:

Ana,72
Ben,64
Cai,81
Dee,59

write() does not add a new line for you: include "\n". writelines() writes a list of strings.

Reading line by line

Loop over the file, or use readline() (one line) or readlines() (a list of all lines). Each line ends with "\n", so strip() it, then split(",") for comma-separated fields. Values read from a file are strings.

f = open("scores.txt", "r")
total = 0
count = 0
for line in f:
    fields = line.strip().split(",")
    total = total + int(fields[1])
    count = count + 1
f.close()
print(count, total / count)

Output:

4 69.0

Loading into a structure

A common pattern is to read a file into a 2D list of records, process the list, then write results:

f = open("scores.txt", "r")
records = []
for line in f.readlines():
    name, mark = line.strip().split(",")
    records.append([name, int(mark)])
f.close()
out = open("passes.txt", "w")
for r in records:
    if r[1] >= 60:
        out.write(f"{r[0]:<5}{r[1]:>4}\n")
out.close()
print(open("passes.txt").read())

Output:

Ana    72
Ben    64
Cai    81

Errors with files

Opening a missing file in "r" mode raises FileNotFoundError; catch it with try/except. Control characters: "\n" line feed, "\r" carriage return, "\t" tab.

Worked example

A file has three lines: 5, 8 and 2. Write code to display their total.

1. f = open("nums.txt", "r")
2. total = 0; for line in f: total = total + int(line.strip())
3. f.close(); print(total)
4. Result: 15

Answer: 15

Check yourself

1. What is displayed when this code runs? ```python f = open("log.txt", "w") f.write("first\n") f.close() f = open("log.txt", "w") f.write("second\n") f.close() f = open("log.txt", "r") print(len(f.readlines())) f.close() ```
   Show answer

   1. Opening in "w" mode erases the file, so only 'second' remains: 1 line.

2. What is displayed when this code runs? ```python f = open("log.txt", "w") f.write("first\n") f.close() f = open("log.txt", "a") f.write("second\n") f.close() f = open("log.txt", "r") print(len(f.readlines())) f.close() ```
   Show answer

   2. "a" adds to the end, so the file now has 2 lines.

3. What is displayed when this code runs? ```python f = open("data.txt", "w") f.write("alpha\nbeta\ngamma\n") f.close() f = open("data.txt", "r") f.readline() print(f.readline().strip()) f.close() ```
   Show answer

   beta. The first readline() reads 'alpha'; the second reads the next line: beta.

4. What is displayed when this code runs? ```python f = open("people.txt", "w") f.write("Zoe,15\nYan,18\nXia,17\n") f.close() f = open("people.txt", "r") oldest = "" best = 0 for line in f: name, age = line.strip().split(",") if int(age) > best: best = int(age) oldest = name f.close() print(oldest) ```
   Show answer

   Yan. Each age is converted to int and compared; the oldest is Yan.

5. Which exception is raised when this code runs? ```python f = open("no_such_file.txt", "r") ```
   • NameError
   • KeyError
   • EOFError
   • FileNotFoundError
   Show answer

   FileNotFoundError. Reading a file that does not exist raises FileNotFoundError.

6. What is displayed when this code runs? ```python f = open("t.txt", "w") f.write("A") f.write("B") f.close() print(open("t.txt").read()) ```
   • A / B
   • AB
   • A B
   • BA
   Show answer

   AB. write() adds no new line, so the file holds AB.

7. This code should total the numbers stored one per line in nums.txt (10, 20, 30). Which line completes it? ```python f = open("nums.txt", "w") f.write("10\n20\n30\n") f.close() f = open("nums.txt", "r") total = 0 for line in f: __________ f.close() print(total) ```
   • `total = total + line`
   • `total = total + line.strip()`
   • `total = int(line)`
   • `total = total + int(line.strip())`
   Show answer

   `total = total + int(line.strip())`. Lines are strings ending in \n, so strip and convert before adding.

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Sources

• Pearson Edexcel International Advanced Subsidiary/Advanced Level in Computer Science specification (XCP01/YCP01), first teaching 2026
• Pearson IAL Computer Science Unit 2 Programming Language Subset (PLS), Python 3
• Pearson IAL Computer Science IAS sample assessment materials (Unit 2 paper and mark scheme)

Last updated 8 November 2026. Spotted a mistake? Tell us.