Introduction

Every real-world application reads or writes data. Whether it’s user preferences, logs, or exported reports, file handling is unavoidable. But files can fail — missing files, permission errors, corrupted data. That’s where exception handling saves you.

In this post:

• Reading and writing TXT, JSON, CSV
• try, except, else, finally
• Best practices for robust code

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Text Files: The Basics

Writing to a TXT file

python

with open("data.txt", "w") as file:
    file.write("Hello, World!")

The with statement automatically closes the file. Never use open() without with in production code.

Reading from a TXT file

python

with open("data.txt", "r") as file:
    content = file.read()
    print(content)

Modes: "r" = read, "w" = write (overwrites), "a" = append.

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JSON Files: Structured Data

JSON is the universal language of APIs and config files.

Writing JSON

python

import json

data = {"name": "Alice", "age": 30}
with open("user.json", "w") as file:
    json.dump(data, file, indent=4)

Reading JSON

python

with open("user.json", "r") as file:
    data = json.load(file)
    print(data["name"])  # Alice

Always use indent for readability when writing JSON manually.

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CSV Files: Tabular Data

CSV (Comma-Separated Values) is everywhere in data exports.

Reading CSV

python

import csv

with open("employees.csv", "r") as file:
    reader = csv.reader(file)
    for row in reader:
        print(row)

Writing CSV

python

with open("output.csv", "w", newline="") as file:
    writer = csv.writer(file)
    writer.writerow(["Name", "Age"])
    writer.writerow(["Bob", 25])

newline="" prevents blank lines between rows on Windows.

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Exception Handling: Preventing Crashes

Files don’t always exist. Networks fail. JSON gets corrupted.

Basic try-except

python

try:
    with open("missing.txt", "r") as file:
        print(file.read())
except FileNotFoundError:
    print("File not found. Creating a new one.")
    with open("missing.txt", "w") as file:
        file.write("Default content")

Multiple Exceptions

python

try:
    value = int(input("Enter number: "))
    result = 10 / value
except ValueError:
    print("That's not a number!")
except ZeroDivisionError:
    print("Cannot divide by zero!")

else and finally

• else: Runs if no exception occurred.
• finally: Always runs (cleanup code).

python

try:
    file = open("log.txt", "r")
except FileNotFoundError:
    print("File missing")
else:
    print("File read successfully")
finally:
    print("Execution complete")

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Best Practices

1. Catch specific exceptions — never use bare except:.
2. Use with for files — automatic closing.
3. Log exceptions in production apps instead of just printing.
4. Validate JSON before parsing.

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Summary

File Type	Read Method	Write Method
TXT	open().read()	open().write()
JSON	json.load()	json.dump()
CSV	csv.reader()	csv.writer()