Handling Exceptions When Processing CSV and JSON Files in Python

1. Python Exception Handling Basics

Python uses the try-except block to catch and handle exceptions. The basic syntax is as follows:

try:
    # code that may raise an exception
except Exception as e:
    # exception handling logic
    print(f"Error occurred: {e}")
else:
    # code executed if no exception occurs
    print("Operation successful!")
finally:
    # code that runs regardless of exception (e.g., close files)
    print("Program execution finished.")

2. Exception Capture in CSV File Processing

2.1 Exceptions When Reading Files

When reading a CSV file, you may encounter FileNotFoundError (file does not exist) or PermissionError (insufficient permissions), among other issues.

Example: Safely Read CSV File

import csv
try:
    with open("data.csv", "r", encoding="utf-8") as file:
        reader = csv.reader(file)
        for row in reader:
            print(row)
except FileNotFoundError:
    print("Error: File not found!")
except PermissionError:
    print("Error: No permission to access the file!")
except csv.Error as e:
    print(f"CSV parsing error: {e}")
except Exception as e:
    print(f"Unknown error: {e}")

2.2 Data Format Exceptions

If the CSV format is irregular (e.g., inconsistent column count), you can catch csv.Error with a try-except block.

Example: Handle CSV Format Errors

try:
    with open("malformed.csv", "r") as file:
        reader = csv.reader(file)
        for row in reader:
            if len(row) != 3:  # assume each row should have 3 columns
                raise ValueError("CSV format error: inconsistent column count")
            print(row)
except ValueError as e:
    print(e)

3. Exception Capture in JSON File Processing

3.1 JSON Parsing Errors

JSON files may raise json.JSONDecodeError when the format is incorrect (missing quotes, mismatched brackets).

Example: Safely Parse JSON File

import json
try:
    with open("data.json", "r", encoding="utf-8") as file:
        data = json.load(file)
        print(data)
except FileNotFoundError:
    print("Error: File not found!")
except json.JSONDecodeError as e:
    print(f"JSON parsing error: {e}")
except Exception as e:
    print(f"Unknown error: {e}")

3.2 Data Type Errors

If the JSON data does not match the expected structure (e.g., missing fields), you can manually check and raise an exception.

Example: Validate JSON Data Structure

try:
    with open("user.json", "r") as file:
        user = json.load(file)
    if "name" not in user or "age" not in user:
        raise ValueError("JSON missing required fields")
    print(f"Username: {user['name']}, Age: {user['age']}")
except ValueError as e:
    print(e)

4. Best Practice: Combine try-except with with Statements

with statement: automatically manages file resources, ensuring files are properly closed.

try-except : catches possible exceptions, preventing program crashes.

Example: Complete Safe CSV + JSON Processing

import csv
import json

def process_files():
    try:
        # Process CSV
        with open("data.csv", "r") as csv_file:
            csv_reader = csv.reader(csv_file)
            for row in csv_reader:
                print(row)

        # Process JSON
        with open("data.json", "r") as json_file:
            data = json.load(json_file)
            print(data)

    except FileNotFoundError:
        print("File not found!")
    except (csv.Error, json.JSONDecodeError) as e:
        print(f"Data parsing error: {e}")
    except Exception as e:
        print(f"Unknown error: {e}")
    finally:
        print("Data processing completed.")

process_files()

5. Summary

Exception handling is essential in file processing to prevent crashes.

CSV files require handling FileNotFoundError , PermissionError , and csv.Error .

JSON files require handling JSONDecodeError and data structure errors.

Best practice: combine with and try-except to ensure resources are released and errors are handled gracefully.