Python新手求助：商品删除功能的文件操作代码异常问题

Hey there! Let's break down the issues in your code and get that product deletion feature working properly. Here's what's going wrong, plus a corrected version of your code with explanations:

Key Issues in Your Original Code #

• You can't directly delete lines from an open file: Using r+ mode and del line doesn't modify the actual file—line is just a temporary variable in your loop, so deleting it does nothing to the stored data.
• No logic to write changes back to the file: Even if you correctly adjusted the product quantity, you didn't save those changes to the file.
• Minor spelling error: delate_product should be delete_product (not a breaking issue, but better for readability).
• No error handling: If the daily archive file doesn't exist yet, your code will crash immediately.
• Unclosed file resource: You don't explicitly close f1, which can lead to resource leaks.

Corrected Code #

import datetime

# Get current date for archive filename
date_now1 = datetime.datetime.now()
archive_date1 = date_now1.strftime("%d.%m.%Y")

# Get user input (clean up whitespace to avoid matching issues)
print("What product do you wish to delete?")
delete_product = input().strip()

try:
    # Read all lines from the archive file first
    with open(archive_date1, "r") as f:
        lines = f.readlines()

    updated_lines = []
    product_found = False

    # Process each line to update or remove the product
    for line in lines:
        cleaned_line = line.strip()
        if not cleaned_line:  # Skip empty lines to avoid errors
            continue

        if delete_product in cleaned_line:
            product_found = True
            # Split line into product name and quantity
            product_parts = cleaned_line.split()
            # Make sure the line has a valid format
            if len(product_parts) >= 2:
                try:
                    quantity = int(product_parts[1])
                    if quantity == 1:
                        # Don't add this line back to remove the product
                        print("Product deleted successfully!")
                    else:
                        # Reduce quantity by 1 and keep the line
                        new_quantity = quantity - 1
                        updated_line = f"{product_parts[0]} {new_quantity}"
                        updated_lines.append(updated_line)
                        print(f"Product quantity reduced to {new_quantity}")
                except ValueError:
                    print(f"Warning: Invalid quantity format in line: {cleaned_line}")
                    updated_lines.append(cleaned_line)  # Keep invalid line as-is
            else:
                print(f"Warning: Malformed line for product: {cleaned_line}")
                updated_lines.append(cleaned_line)
        else:
            # Keep lines that don't match the product
            updated_lines.append(cleaned_line)

    # Write the updated content back to the file
    with open(archive_date1, "w") as f:
        f.write("\n".join(updated_lines))

    if not product_found:
        print("Error: That product wasn't found in the archive.")

except FileNotFoundError:
    print(f"Error: The archive file {archive_date1} doesn't exist yet.")

What's Improved? #

• Safe file handling: Uses with statements to automatically close files, preventing resource leaks.
• Proper file modification: Reads all content into memory, processes it, then rewrites the entire file—this is the standard way to modify file contents in Python.
• Error resilience: Catches missing files and invalid quantity values, so your program won't crash unexpectedly.
• Better user feedback: Tells you if the product wasn't found, if there's a formatting error, or if the quantity was successfully reduced.
• Cleaner input handling: Uses strip() to remove extra spaces from user input, so accidental spaces won't break product matching.

内容的提问来源于stack exchange，提问作者Krystian Dorsz