如何动态替换Dynamodb中的where条件参数？

import boto3

def update_dynamodb_item(table_name, key, update_expression, expression_attribute_names, expression_attribute_values):
    dynamodb = boto3.client('dynamodb')
    dynamodb.update_item(
        TableName=table_name,
        Key=key,
        UpdateExpression=update_expression,
        ExpressionAttributeNames=expression_attribute_names,
        ExpressionAttributeValues=expression_attribute_values
    )

# 替换的属性名称和属性值
attribute_name = "age"
attribute_value = 25

# 自定义的占位符
placeholder = "#placeholder"

# 创建表达式属性名称映射的Map
expression_attribute_names = {
    placeholder: attribute_name
}

# 创建表达式属性值映射的Map
expression_attribute_values = {
    ":value": attribute_value
}

# 构建更新表达式
update_expression = "SET #placeholder = :value"

# 调用函数来更新DynamoDB表中的数据
update_dynamodb_item("my_table", {"id": {"S": "123"}}, update_expression, expression_attribute_names, expression_attribute_values)