Python Files, Exceptions and Modules Practice

Practise reading and writing files, handling errors with try/except, and using the json, datetime, re and collections modules.

Intermediate9 problemsUpdated October 23, 2026

Review first: File Handling, Exceptions, JSON, Date & Time, Regular Expressions, Modules

1.Write a file, then read it

Intermediate

Write three lines (Asha,88, Ravi,95, Meera,79) to a file called scores.txt. Then read it back and print each name with its score, and the highest score.

Show hint

Open with "w" to write and "r" to read, inside with blocks. Each line needs a \n when writing, and .strip() when reading.

Show solution

Python

with open("scores.txt", "w", encoding="utf-8") as f:
    f.write("Asha,88\n")
    f.write("Ravi,95\n")
    f.write("Meera,79\n")

best = 0
with open("scores.txt", "r", encoding="utf-8") as f:
    for line in f:
        name, score = line.strip().split(",")
        score = int(score)
        print(name, score)
        best = max(best, score)

print("Highest:", best)

Output

Asha 88
Ravi 95
Meera 79
Highest: 95

The with statement closes the file automatically, even if an error happens inside the block.

2.Append to a log

Intermediate

Append the lines started, processing and finished to app.log in three separate open() calls, then print the file's contents and how many lines it has.

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Mode "a" adds to the end of a file; mode "w" would erase it each time.

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Python

for message in ["started", "processing", "finished"]:
    with open("app.log", "a", encoding="utf-8") as f:
        f.write(message + "\n")

with open("app.log", encoding="utf-8") as f:
    content = f.read()

print(content, end="")
print(len(content.splitlines()), "lines")

Output

started
processing
finished
3 lines

3.Convert values safely
Intermediate
Convert every item in raw = ["10", "abc", "7.5", "", "42"] to an integer. Skip the ones that cannot be converted, printing a message for each, then print the valid numbers and their total.
Show hint
int() raises a ValueError for text that is not a whole number. Catch it with try / except ValueError.
Show solution
Python
raw = ["10", "abc", "7.5", "", "42"] numbers = [] for item in raw: try: numbers.append(int(item)) except ValueError: print(f"Skipping {item!r}") print(numbers, sum(numbers))
Output
Skipping 'abc' Skipping '7.5' Skipping '' [10, 42] 52
{item!r} shows the value with quotes, which makes the empty string '' visible in the message.

4.try, except, else, finally

Intermediate

Write divide(a, b) that prints the result of a / b in an else block, prints Cannot divide by zero for a ZeroDivisionError, and always prints done in a finally block. Call divide(10, 4) and divide(1, 0).

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else runs only when no exception was raised; finally runs every time.

Show solution

Python

def divide(a, b):
    try:
        result = a / b
    except ZeroDivisionError:
        print("Cannot divide by zero")
    else:
        print("Result:", result)
    finally:
        print("done")


divide(10, 4)
divide(1, 0)

Output

Result: 2.5
done
Cannot divide by zero
done

5.A custom exception

Intermediate

Create an InsufficientFundsError exception. Write withdraw(balance, amount) that raises it when the amount is more than the balance, and returns the new balance otherwise. Call it with (500, 200) and (500, 800), catching the error.

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A custom exception is a class that inherits from Exception. Raise it with raise InsufficientFundsError("message").

Show solution

Python

class InsufficientFundsError(Exception):
    pass


def withdraw(balance, amount):
    if amount > balance:
        raise InsufficientFundsError(f"Cannot withdraw {amount}; balance is {balance}")
    return balance - amount


for amount in [200, 800]:
    try:
        print("New balance:", withdraw(500, amount))
    except InsufficientFundsError as error:
        print("Error:", error)

Output

New balance: 300
Error: Cannot withdraw 800; balance is 500

6.Save and load JSON
Intermediate
Convert settings = {"theme": "dark", "font_size": 14, "plugins": ["git", "lint"]} to a JSON string with sorted keys and an indent of 2, and print it. Then parse the string back and print the second plugin.
Show hint
json.dumps(obj, indent=2, sort_keys=True) makes the string; json.loads(text) parses it.
Show solution
Python
import json settings = {"theme": "dark", "font_size": 14, "plugins": ["git", "lint"]} text = json.dumps(settings, indent=2, sort_keys=True) print(text) loaded = json.loads(text) print(loaded["plugins"][1])
Output
{ "font_size": 14, "plugins": [ "git", "lint" ], "theme": "dark" } lint
To work with files, use json.dump(obj, f) and json.load(f) (without the s), which write to and read from an open file.
7.Days between dates
Intermediate
For a course that starts on 2026-11-02 and ends on 2027-01-15, print the number of days between the dates, the date 30 days after the start, and the start date formatted like Monday, 02 November 2026.
Show hint
Subtracting two date objects gives a timedelta; use .days. Add a timedelta(days=30), and format with strftime("%A, %d %B %Y").
Show solution
Python
from datetime import date, timedelta start = date(2026, 11, 2) end = date(2027, 1, 15) print((end - start).days) print(start + timedelta(days=30)) print(start.strftime("%A, %d %B %Y"))
Output
74 2026-12-02 Monday, 02 November 2026
date.fromisoformat("2026-11-02") converts a YYYY-MM-DD string into a date object, which is handy when dates come from a file or form.
8.Extract with a regular expression
Intermediate
From text = "Call 98200-11111 or 98300-22222. Office: 022-2345678.", extract every mobile number in the form 5 digits, a dash, 5 digits. Then check whether "411001" and "41100" are valid 6-digit PIN codes.
Show hint
re.findall(r"\d{5}-\d{5}", text) finds all matches. re.fullmatch(r"\d{6}", s) checks that the whole string matches.
Show solution
Python
import re text = "Call 98200-11111 or 98300-22222. Office: 022-2345678." print(re.findall(r"\d{5}-\d{5}", text)) for pin in ["411001", "41100"]: print(pin, bool(re.fullmatch(r"\d{6}", pin)))
Output
['98200-11111', '98300-22222'] 411001 True 41100 False
Always write patterns as raw strings (r"...") so that backslashes reach the regex engine unchanged. re.search would accept "4110012" for \d{6} because it only needs a match somewhere; fullmatch requires the entire string to match.
9.Use the standard library
Intermediate
Using collections.Counter, print the two most common letters in "mississippi" with their counts. Then use the math module to print the square root of 2 rounded to 4 decimals and math.ceil(7 / 2).
Show hint
Counter(text).most_common(2) returns a list of (letter, count) pairs.
Show solution
Python
import math from collections import Counter print(Counter("mississippi").most_common(2)) print(round(math.sqrt(2), 4)) print(math.ceil(7 / 2))
Output
[('i', 4), ('s', 4)] 1.4142 4
"i" and "s" both appear 4 times. When counts tie, most_common keeps the order in which the items were first seen.

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