有谁知道如何解决这个问题。我正在检查偶数行中是否有“1850年人口普查”这一短语。如果它在该行中找到该短语，则应保留该行及其上一行。如果没有找到，则应删除该行及其上一行。我使用的数据集是：

(didn't粘贴在其他行，但还有更多）
我使用的代码是：

import csv

def scan_csv_file(file_path):
    """
    This function scans a CSV file and performs the following operations:
    - Scans the even rows for the phrase "Census 1850" anywhere in the row
    - If found, keeps that cell and deletes the cell above it
    - If not found, deletes that row and one row above it
    - Checks only the even rows for this
    
    Parameters:
    file_path (str): The path to the CSV file to be scanned
    
    Returns:
    None
    """
    try:
        # Open the CSV file
        with open(file_path, 'r') as file:
            # Read the CSV file
            csv_reader = csv.reader(file)
            # Create a list to store the rows to be written to a new file
            new_rows = []
            # Create a variable to keep track of the current row number
            row_num = 0
            # Initialize the new_row variable outside the loop
            new_row = []
            # Loop through each row in the CSV file
            for row in csv_reader:
                # Check if the row number is even
                if row_num % 2 == 0:
                    # Check if the phrase "Census 1850" is in the row
                    if "Census 1850" in ','.join(row):
                        # Keep the current cell and delete the cell above it
                        new_row = row[1:]
                    else:
                        # Delete the current row and the row above it
                        if len(new_rows) > 0:
                            new_rows.pop()
                            continue
                else:
                    # Keep the current row
                    new_row = row
                # Append the new row to the list of rows
                new_rows.append(new_row)
                # Increment the row number
                row_num += 1
        # Overwrite the existing CSV file with the new rows
        with open(file_path, 'w', newline='') as file:
            csv_writer = csv.writer(file)
            csv_writer.writerows(new_rows)
        print("CSV file modified successfully.")
    except Exception as e:
        # Log the error
        print(f"Error: {e}")

# Provide the path to your CSV file
file_path = r"C:\Users\My Name\Downloads\tracing_the_land_2_test.csv"

scan_csv_file(file_path)

但是，它只是不断地删除文档中的所有内容。有人能帮我吗？