在Cloud Functions中创建Cloud Storage CSV文件遇权限问题求助

这个问题我碰到过好多次啦——Cloud Functions的运行环境里，只有/tmp目录是支持读写操作的临时存储区，你直接在当前工作目录创建test.csv，自然会触发只读文件系统的错误。

你的原代码（问题出在这里） #

def upload_blob(bucket_name, source_file_name, destination_blob_name):
    storage_client = storage.Client()
    bucket = storage_client.get_bucket(bucket_name)
    blob = bucket.blob(destination_blob_name)
    blob.upload_from_file(source_file_name)

message = "Data for CSV file"
csv = open('test.csv', "w") # 这里出错了！
csv.write(message)
with open('/tmp/test.csv', 'r') as file_obj:
    upload_blob('test-bucket', file_obj, 'test.csv')

你遇到的错误 #

OSError: [Errno 30] Read-only file system: 'test.csv'

修复方案 #

直接把文件创建在/tmp目录下，另外推荐用with语句来处理文件，它会自动帮你关闭文件句柄，确保写入的内容被正确刷到磁盘，避免资源泄漏：

def upload_blob(bucket_name, source_file_name, destination_blob_name):
    storage_client = storage.Client()
    bucket = storage_client.get_bucket(bucket_name)
    blob = bucket.blob(destination_blob_name)
    blob.upload_from_file(source_file_name)

message = "Data for CSV file"
# 直接在/tmp目录下创建并写入文件
with open('/tmp/test.csv', "w") as csv_file:
    csv_file.write(message)

# 读取/tmp里的文件并上传到存储桶
with open('/tmp/test.csv', 'r') as file_obj:
    upload_blob('test-bucket', file_obj, 'test.csv')

额外小提示 #

• /tmp目录的存储空间有限（目前Cloud Functions最多提供512MB临时存储），如果你的CSV文件很大，要注意别超限额。
• 函数执行结束后，/tmp里的临时文件会被自动清除，不用手动删除；但如果是大文件，上传完成后手动删除能提前释放资源。
• 如果要生成规范的CSV（比如处理含逗号、换行符的内容），用Python内置的csv模块会更可靠，示例如下：

import csv

def upload_blob(bucket_name, source_file_name, destination_blob_name):
    storage_client = storage.Client()
    bucket = storage_client.get_bucket(bucket_name)
    blob = bucket.blob(destination_blob_name)
    blob.upload_from_file(source_file_name)

# 用csv模块生成标准CSV格式的数据
data = [["Name", "Age"], ["Alice", 30], ["Bob", 25]]
with open('/tmp/test.csv', 'w', newline='') as csv_file:
    writer = csv.writer(csv_file)
    writer.writerows(data)

with open('/tmp/test.csv', 'r') as file_obj:
    upload_blob('test-bucket', file_obj, 'test.csv')

内容的提问来源于stack exchange，提问作者TeeKay