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Computer Science · Class 12 · Text Files
ProgramsBoard pattern⏱️ 22 min read

Text File Practice Programs

Board questions on text files are the same handful of programs, dressed differently — count something, find something, copy something, remove something. Here are ten of them, written the way the paper asks: as a function with a name, doing one job.

1The file every program reads

All ten programs run on the same five-line file, story.txt. Every output on this page was produced by running the program against it.

story.txt
India is a land of many festivals.
The lights of Diwali are famous.
A festival brings the people together.
Every state has its own colours.
People travel home to celebrate them.
How to answer one of these in the exam
Open the file, set your counter to 0, walk the file with for line in f, test the thing being asked about, close the file, print the answer. Nine of the ten below are that skeleton with a different if in the middle.

2Program 1 — count the lines beginning with ‘A’

📋 The problem

Write a function to count the number of lines in story.txt that begin with the letter ‘A’ or ‘a’.

count_a_lines.py
def count_a_lines():
    f = open('story.txt', 'r')
    count = 0

    for line in f:
        if line[0] == 'A' or line[0] == 'a':
            count = count + 1

    f.close()
    print('Lines beginning with A:', count)

count_a_lines()
Output
Lines beginning with A: 1
for line in f:

One line at a time. The line still carries its \n, which does not matter here.

line[0]

The first character of the line. This is the only part the question is about.

== 'A' or line[0] == 'a'

Both cases, because the question says the letter A, not the capital A. line[0] in 'Aa' says the same thing more briefly.

Where line[0] does break
Reading with for line in f is safe: a blank line in the file arrives as '\n', which has a character 0. But splitting the text yourself with data.split('\n') produces genuinely empty strings — one for each blank line, and one at the end — and line[0] on those raises IndexError: string index out of range. line.startswith('A') is safe on every string, empty ones included.

3Program 2 — count vowels, consonants, uppercase and lowercase

📋 The problem

Write a function to count the vowels, consonants, uppercase letters and lowercase letters in story.txt.

count_letters.py
def count_letters():
    f = open('story.txt', 'r')
    data = f.read()
    f.close()

    vowels = 0
    consonants = 0
    uppercase = 0
    lowercase = 0

    for ch in data:
        if ch.isalpha():
            if ch in 'AEIOUaeiou':
                vowels = vowels + 1
            else:
                consonants = consonants + 1
            if ch.isupper():
                uppercase = uppercase + 1
            else:
                lowercase = lowercase + 1

    print('Vowels:', vowels)
    print('Consonants:', consonants)
    print('Uppercase letters:', uppercase)
    print('Lowercase letters:', lowercase)

count_letters()
Output
Vowels: 57
Consonants: 85
Uppercase letters: 6
Lowercase letters: 136
isalpha() first, then the two questions
Full stops, spaces and newlines are not letters, and counting them as consonants is the usual wrong answer. ch.isalpha() throws them out, and everything inside that if is then about a real letter. Notice both questions are asked about the same character: vowel-or-consonant, and upper-or-lower.

4Program 3 — count the words longer than four characters

📋 The problem

Write a function to count the words in story.txt that have more than four characters.

long_words.py
def long_words():
    f = open('story.txt', 'r')
    count = 0

    for line in f:
        for word in line.split():
            if len(word) > 4:
                count = count + 1

    f.close()
    print('Words longer than 4 characters:', count)

long_words()
Output
Words longer than 4 characters: 16
split() with no argument
line.split() breaks the line at every run of blank space and drops the empty pieces, so it works even where two spaces crept in. The full stop stays attached to the last word, which makes festivals. ten characters — add .strip('.,') if the question means the word alone.

5Program 4 — display the lines shorter than 35 characters

📋 The problem

Write a function to display every line of story.txt that is fewer than 35 characters long.

short_lines.py
def short_lines():
    f = open('story.txt', 'r')

    for line in f:
        if len(line.strip()) < 35:
            print(line.strip())

    f.close()

short_lines()
Output
India is a land of many festivals.
The lights of Diwali are famous.
Every state has its own colours.
strip() before you measure
Without it, the \n counts as a character and every line measures one longer than it looks. On a question with a boundary like “fewer than 35”, that single character is the difference between the right answer and the wrong one.

6Program 5 — copy the lines containing a word into another file

📋 The problem

Write a function that copies every line of story.txt containing the word India into a new file india.txt, and reports how many were copied.

copy_matching.py
def copy_matching(word):
    source = open('story.txt', 'r')
    target = open('india.txt', 'w')
    count = 0

    for line in source:
        if word in line:
            target.write(line)
            count = count + 1

    source.close()
    target.close()
    print('Lines copied:', count)

copy_matching('India')
print(open('india.txt').read())
Output
Lines copied: 1
India is a land of many festivals.
target = open('india.txt', 'w')

Both files are open at once — one to read from, one to write to. 'w' creates india.txt if it is not there, and empties it if it is.

if word in line:

Membership on a string: does this line contain that text anywhere? This is a substring test, so 'India' would also match 'Indian'.

target.write(line)

The line still has its \n on the end, so the copy comes out with proper lines. Nothing needs adding.

7Program 6 — display the file with line numbers

📋 The problem

Write a function to display the contents of story.txt with each line numbered from 1.

numbered.py
def numbered():
    f = open('story.txt', 'r')
    number = 1

    for line in f:
        print(number, line.strip())
        number = number + 1

    f.close()

numbered()
Output
1 India is a land of many festivals.
2 The lights of Diwali are famous.
3 A festival brings the people together.
4 Every state has its own colours.
5 People travel home to celebrate them.

8Program 7 — find the longest line

📋 The problem

Write a function to find and display the longest line in story.txt, along with its length.

longest_line.py
def longest_line():
    f = open('story.txt', 'r')
    longest = ''

    for line in f:
        line = line.strip()
        if len(line) > len(longest):
            longest = line

    f.close()
    print('The longest line is:')
    print(longest)
    print('Its length is', len(longest))

longest_line()
Output
The longest line is:
A festival brings the people together.
Its length is 38
The running-best pattern
Start with the empty string, then keep whatever beats what you are holding. It is the same shape as finding the largest number in a list, which you wrote in Class 11 — only the comparison changed, from n > biggest to len(line) > len(longest).

9Program 8 — count how many times a word appears

📋 The problem

Write a function that counts how many times a given word appears in story.txt, ignoring capitals and punctuation.

count_word.py
def count_word(word):
    f = open('story.txt', 'r')
    count = 0

    for line in f:
        for w in line.split():
            if w.strip('.,').lower() == word.lower():
                count = count + 1

    f.close()
    print(word, 'appears', count, 'times')

count_word('the')
count_word('festival')
Output
the appears 2 times
festival appears 1 times
Not data.count(word)
count() would find the inside together and them and answer 3. When the question says word, split into words and compare whole words — and .lower() on both sides so that The counts too.

10Program 9 — write records, then read them back

📋 The problem

Write one function that stores names and marks in result.txt, one record per line, and another that displays the students who scored 75 or more.

results.py
def create_file():
    names = ['Ravi', 'Meera', 'Amit']
    marks = [78, 91, 65]

    f = open('result.txt', 'w')
    for i in range(len(names)):
        f.write(names[i] + ',' + str(marks[i]) + '\n')
    f.close()


def show_toppers():
    f = open('result.txt', 'r')

    for line in f:
        name, mark = line.strip().split(',')
        if int(mark) >= 75:
            print(name, 'scored', mark)

    f.close()

create_file()
show_toppers()
Output
Ravi scored 78
Meera scored 91
f.write(names[i] + ',' + str(marks[i]) + '\n')

A record is a line you build yourself. str() is needed because write() refuses a number, and the \n is needed because write() adds nothing.

line.strip().split(',')

strip() first, or the mark would arrive as '78\n'. split(',') then gives a two-item list, which the two names on the left unpack.

int(mark)

Everything read from a text file is a string. '91' > '9' is False, so comparing without int() gives silently wrong answers.

11Program 10 — remove every line containing a word

📋 The problem

Write a function that removes from story.txt every line containing a given word, and reports how many were removed.

remove_lines.py
import os

def remove_lines(word):
    source = open('story.txt', 'r')
    temp = open('temp.txt', 'w')
    removed = 0

    for line in source:
        if word in line:
            removed = removed + 1
        else:
            temp.write(line)

    source.close()
    temp.close()

    os.remove('story.txt')
    os.rename('temp.txt', 'story.txt')
    print('Lines removed:', removed)

remove_lines('Diwali')
print(open('story.txt').read())
Output
Lines removed: 1
India is a land of many festivals.
A festival brings the people together.
Every state has its own colours.
People travel home to celebrate them.
Why a temporary file
The original is only ever read, so nothing can be lost until the new version is complete on the disk. Opening story.txt in 'w' instead would empty it at once, and a crash halfway through would take the lot.

12Run one yourself

The file is here in the browser. Change the program to answer a different question — lines ending in a full stop, words starting with a capital, characters excluding spaces:

practice.py
📄 story.txt

13The five patterns behind all ten

Count with a condition
count = 0 … if …: count = count + 1

Programs 1, 3, 8, 10. The only thing that changes is the test.

Count per character
for ch in data:

Program 2. read() the file into one string first, then walk the characters.

Display with a condition
if …: print(line.strip())

Programs 4 and 6. No counter at all — the answer is the printing.

Two files at once
source = open(…, 'r'); target = open(…, 'w')

Programs 5 and 10. One is read, one is written, and both get closed.

Running best
if len(line) > len(longest): longest = line

Program 7. Hold the best so far, replace it when something beats it.

✍️ Now write these yourself
  1. 1

    Count the lines that end with a full stop.

    Hint · line.strip() first, then line.endswith('.').

  2. 2

    Count the characters in the file, not counting spaces.

    Hint · Walk the characters and skip the ones where ch == ' '.

  3. 3

    Display every word that starts with a capital letter, one per line.

    Hint · word[0].isupper() — and split() the line first.

  4. 4

    Copy story.txt into copy.txt with the lines in reverse order.

    Hint · readlines() gives a list, and lists have reverse().

  5. 5

    Ask the user for a word and replace every occurrence of it in the file with ****.

    Hint · read(), replace(), write it back in mode 'w'.

Quick Check

Why does a line-length program call line.strip() before len()?

Quick Check

A program reads '78' from a file and compares it with 75. What must it do first?

Quick Check

Which counts the WORD 'the' correctly?

Quick Check

Reading with for line in f, a blank line in the file comes back as...

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