File Handling with Copilot Prompts

In real-world Python projects, you often need to work with files — reading data from files, saving data for later, or exchanging data with others.

Python makes file handling straightforward, and with Copilot, you can write these scripts even faster by describing what you want in a clear prompt.

Why Learn File Handling?

• Store data between program runs (e.g., save a score or user preferences).
• Process large data files (logs, datasets, text files).
• Interact with other systems via files (e.g., importing/exporting CSV or JSON).

Reading and Writing Text Files

The most basic file operations are reading and writing simple text files.

Prompt

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# Write a Python script to read a file and print its contents

Example Copilot Suggestion

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def read_file(filename):
    try:
        with open(filename, 'r') as f:
            contents = f.read()
            print(contents)
    except FileNotFoundError:
        print("File not found.")

Explanation

• open(filename, 'r'): Opens the file in read mode.
• with: Automatically closes the file when finished (good practice).
• f.read(): Reads the entire file as a single string.
• except FileNotFoundError: Catches the error if the file doesn’t exist.

Practice Example

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read_file("sample.txt")

If sample.txt exists, it prints the contents. Otherwise, it shows "File not found."

Writing to a File

To save data to a file, you open it in write mode ('w').

Example

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def write_file(filename, text):
    with open(filename, 'w') as f:
        f.write(text)
        print("Data written successfully.")

Explanation

• 'w': Overwrites the file if it exists. Creates a new file if it doesn't.
• f.write(text): Writes the given text to the file.

Practice Example

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write_file("output.txt", "Hello, this is my first file written from Python!")

Working with CSV Files

CSV (Comma-Separated Values) files are commonly used to store tabular data, like spreadsheets.

Reading CSV

Prompt

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# Write a Python script to read a CSV file and print each row

Copilot Suggestion

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import csv

def read_csv(filename):
    try:
        with open(filename, 'r', newline='') as csvfile:
            reader = csv.reader(csvfile)
            for row in reader:
                print(row)
    except FileNotFoundError:
        print("CSV file not found.")

Explanation

• import csv: Python’s built-in CSV module.
• csv.reader(): Reads each row as a list.
• Looping through reader: Prints each row in the file.

Writing CSV

Prompt

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# Write a function to write a list of rows to a CSV file

Copilot Suggestion

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import csv

def write_csv(filename, data):
    with open(filename, 'w', newline='') as csvfile:
        writer = csv.writer(csvfile)
        writer.writerows(data)
        print("CSV file written successfully.")

Explanation

• writerows(data): Writes a list of lists, each sublist becomes a row.

Practice Example

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rows = [
    ["Name", "Age", "City"],
    ["Alice", "30", "New York"],
    ["Bob", "25", "Los Angeles"]
]
write_csv("people.csv", rows)
read_csv("people.csv")

Working with JSON Files

JSON (JavaScript Object Notation) is widely used for storing structured data, especially when working with web APIs.

Writing JSON

Prompt

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# Write a function to save a dictionary as a JSON file

Copilot Suggestion

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import json

def save_to_json(filename, data):
    with open(filename, 'w') as jsonfile:
        json.dump(data, jsonfile, indent=4)
        print("JSON file saved successfully.")

Explanation

• import json: Python’s built-in module for JSON handling.
• json.dump(): Saves Python dictionary as a JSON file.
• indent=4: Makes the JSON file nicely formatted and easy to read.

Practice Example

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data = {
    "name": "John",
    "age": 28,
    "city": "Chicago",
    "skills": ["Python", "Data Analysis"]
}

save_to_json("profile.json", data)

Reading JSON

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import json

def read_from_json(filename):
    try:
        with open(filename, 'r') as jsonfile:
            data = json.load(jsonfile)
            print(data)
    except FileNotFoundError:
        print("JSON file not found.")

Practice Example

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read_from_json("profile.json")

Key Takeaways

• Use open() with 'r' for reading, 'w' for writing.
• Always close files; using with does this automatically.
• Use csv module for spreadsheet-like data.
• Use json module for structured, nested data.
• Copilot can generate full file-handling functions for you — start with a clear, specific prompt.

Mini Challenge

Prompt

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# Write a function that appends a new line to an existing text file, creating it if it doesn't exist

Try generating it with Copilot and test by appending different messages.

Practice Exercises

1. Write a function to count the number of lines in a text file.
2. Create a function that loads a list of dictionaries from a JSON file.
3. Write a function that saves user input (name and email) into a CSV file.

Extra Tips

• Test file-handling code carefully to avoid overwriting important files.
• Check for file existence using try-except blocks.
• Start small: first print text to a file, then try reading it back.