Python CSV Writer无法添加Whip列，计算结果未输出问题求助

Let's walk through the issues in your code step by step to get that WHIP calculation showing up in your output file:

Key Issues in the Original Code #

• Incorrect file opening mode: In Python 3, csv.DictReader doesn't require binary mode (rb). Using 'r' (text mode) with newline='' ensures proper CSV handling and avoids extra blank lines in the output.
• Missing 'Whip' in output fields: Your fieldnames list didn't include the new 'Whip' column, so the writer wouldn't output it even if you calculated it.
• Dictionary manipulation error: line is a dictionary (from DictReader), not a list—you can't use append() on it. Instead, assign the WHIP value to a new key in the dictionary.
• String-to-number conversion: All values read from CSV are strings. You need to convert BB, H, and IPouts to integers before doing math, otherwise you'll get errors or nonsensical results.
• Case-sensitive header typo: You wrote line['Ipouts'] but the CSV header is IPouts (uppercase I and P)—this would throw a KeyError and crash the script.

Corrected Code #

import csv

print('Enter start year: ')
startYear = input()
print('Enter end year: ')
endYear = input()

# Use text mode with newline='' for proper CSV handling in Python 3
with open('Pitching.csv', 'r', newline='') as csv_file:
    csv_reader = csv.DictReader(csv_file)
    
    # Automatically include all original headers plus the new 'Whip' column
    fieldnames = csv_reader.fieldnames + ['Whip']
    
    with open('new_stats.csv', 'w', newline='') as new_file:
        csv_writer = csv.DictWriter(new_file, fieldnames=fieldnames)
        csv_writer.writeheader()
        
        for line in csv_reader:
            currentYear = line['yearID']
            # Convert years to integers for valid comparison
            if int(currentYear) >= int(startYear) and int(currentYear) <= int(endYear):
                # Convert CSV string values to integers for calculation
                walks = int(line['BB'])
                hits = int(line['H'])
                inningsPitched = int(line['IPouts'])  # Fixed case mismatch here
                
                # Calculate WHIP: (Walks + Hits) / Innings Pitched (IPouts divided by 3)
                innings = inningsPitched / 3.0
                # Avoid division by zero if no innings were pitched
                if innings > 0:
                    whip = (walks + hits) / innings
                else:
                    whip = 0.0  # Adjust this handling if needed (e.g., leave blank)
                
                # Add WHIP to the dictionary as a new key-value pair
                line['Whip'] = round(whip, 3)  # Round to 3 decimals for standard stat formatting
                csv_writer.writerow(line)

Additional Notes #

• I added a check for division by zero (if inningsPitched is 0) to prevent runtime errors—feel free to adjust this handling if you want a different placeholder or behavior.
• Rounding the WHIP value to 3 decimal places matches standard baseball stat formatting, but you can remove the round() call if you want full precision.
• Using csv_reader.fieldnames + ['Whip'] instead of hardcoding all headers makes the script more maintainable if the original CSV ever gets updated with new columns.

内容的提问来源于stack exchange，提问作者B.Strainer