如何移除CSV文件第2列每行分隔符(.)后的内容？附代码求助

DevOps 小满

2026-5-8

Fixing CSV Time Column Millisecond Removal

Hey there! Let's get your CSV processing sorted out. I see where you might have hit snags—let's break this down and get a working solution.

First, Fix the Column Index Issue

CSV rows in Python's csv module are zero-indexed. If you're targeting the second column (labeled "Time"), that's actually row[1], not row[2] (that would be the third column). That's probably why your earlier row[2][:-4] wasn't working as expected.

The Correct Processing Logic

For each time value:

Check if it contains a . (the millisecond separator)
If yes, split the string at the . and keep the first part
If no, leave the value as-is

Full Working Code

We'll use with statements to handle file opening/closing safely (no need to manually call close()), and write the modified rows to a new CSV file:

import csv

# Open original CSV and create new output CSV
with open('Book1.csv', 'r') as input_file, open('Book1_no_ms.csv', 'w', newline='') as output_file:
    reader = csv.reader(input_file)
    writer = csv.writer(output_file)
    
    for row in reader:
        # Copy the row to avoid modifying original data
        modified_row = row.copy()
        # Target the second column (index 1)
        time_value = modified_row[1]
        # Remove milliseconds if present
        if '.' in time_value:
            modified_row[1] = time_value.split('.')[0]
        # Write the row to the new file
        writer.writerow(modified_row)

Why This Works

with statements ensure files are properly closed even if an error occurs
row.copy() prevents accidental changes to the original row data
split('.')[0] cleanly grabs everything before the millisecond separator—this works reliably even if the millisecond portion has more/less than one digit
Rows without milliseconds stay untouched, exactly as you wanted