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Object Storage Service:Append upload (Python SDK V2)

Last Updated:Jul 31, 2025

Append upload lets you append data to the end of an existing appendable object. This topic describes how to perform an append upload using the OSS SDK for Python V2.

Precautions

  • The sample code in this topic uses the China (Hangzhou) region, which has the region ID cn-hangzhou, as an example. By default, a public endpoint is used. If you want to access OSS from other Alibaba Cloud services in the same region as OSS, you must use an internal endpoint. For more information about the mappings between OSS regions and endpoints, see OSS regions and endpoints.

  • If the object does not exist, calling the append upload method creates an appendable object.

  • If the object exists:

    • If the object is an appendable object and the specified append position is the same as the current length of the object, the content is appended to the end of the object.

    • If the object is an appendable object but the specified append position is not the same as the current length of the object, a PositionNotEqualToLength exception is thrown.

    • If the object is not an appendable object, such as a normal object that is uploaded using simple upload, an ObjectNotAppendable exception is thrown.

Permissions

By default, an Alibaba Cloud account has full permissions. RAM users or RAM roles under an Alibaba Cloud account do not have any permissions by default. The Alibaba Cloud account or account administrator must grant operation permissions through RAM Policy or Bucket Policy.

API

Action

Definition

AppendObject

oss:PutObject

You can call this operation to upload an object by appending the object to an existing object.

oss:PutObjectTagging

When uploading an object by appending the object to an existing object, if you specify object tags through x-oss-tagging, this permission is required.

Method definitions

For append upload scenarios, the Python SDK V2 adds the AppendFile method to simulate file read and write operations on objects in a bucket. The following table describes the AppendFile and AppendObject methods.

Method

Description

AppendFile

Provides the same features as the AppendObject method.

Optimizes fault tolerance for retransmissions after a failure.

AppendObject

Performs an append upload. The final object can be up to 5 GiB in size.

Supports CRC-64 data validation (enabled by default).

Supports progress bar charts.

AppendFile: The append upload API of the Premium Edition

You can call the AppendFile method to upload data in append mode. If the object does not exist, an appendable object is created. If the object exists but is not an appendable object, an error is returned.

The following code shows the definition of the AppendFile method.

append_file(bucket: str, key: str, request_payer: str | None = None, create_parameter: AppendObjectRequest | None = None, **kwargs) → AppendOnlyFile

Request parameters

Parameter

Type

Description

bucket

str

The name of the bucket.

key

str

The name of the object.

RequestPayer

str

If the pay-by-requester mode is enabled, set this parameter to 'requester'.

CreateParameter

AppendObjectRequest

The metadata of the object that is set for the first upload, including ContentType, Metadata, permissions, and storage class. For more information, see AppendObjectRequest.

Return values

Type

Description

AppendOnlyFile

The instance of the appendable file. For more information, see AppendOnlyFile.

The following table describes the methods included in the AppendOnlyFile class.

Method

Description

Close()

Closes the file handle and releases resources.

write(b)

Writes byte data to the file and returns the number of bytes written.

write_from(b: str | bytes | Iterable[bytes] | IO[str] | IO[bytes])

Writes any data to the file and returns the number of bytes written.

For the complete definition of the AppendFile method, see append_file.

AppendObject: The append upload API of the Basic Edition

append_object(request: AppendObjectRequest, **kwargs) → AppendObjectResult

Request parameters

Parameter

Type

Description

request

AppendObjectRequest

The request parameters. For more information, see AppendObjectRequest.

Return values

Type

Description

AppendObjectResult

The return value. For more information, see AppendObjectResult.

For the complete definition of the AppendObject method, see append_object.

Examples

(Recommended) Use AppendFile to perform an append upload

import argparse
import alibabacloud_oss_v2 as oss

# Create a command-line argument parser and describe the purpose of the script: This example shows how to append data to an OSS object.
parser = argparse.ArgumentParser(description="append file sample")

# Add the --region command-line argument, which specifies the region where the bucket is located. This argument is required.
parser.add_argument('--region', help='The region in which the bucket is located.', required=True)
# Add the --bucket command-line argument, which specifies the name of the bucket to operate on. This argument is required.
parser.add_argument('--bucket', help='The name of the bucket.', required=True)
# Add the --endpoint command-line argument, which specifies the domain name that other services can use to access OSS. This argument is optional.
parser.add_argument('--endpoint', help='The domain names that other services can use to access OSS')
# Add the --key command-line argument, which specifies the key of the object (file) in OSS. This argument is required.
parser.add_argument('--key', help='The name of the object.', required=True)

def main():
    # Parse the command-line arguments to obtain the user-provided values.
    args = parser.parse_args()

    # Load the authentication information required to access OSS from environment variables for identity verification.
    credentials_provider = oss.credentials.EnvironmentVariableCredentialsProvider()

    # Create a configuration object using the default configurations of the SDK and set the credential provider.
    cfg = oss.config.load_default()
    cfg.credentials_provider = credentials_provider
    cfg.region = args.region

    # If a custom endpoint is provided, update the endpoint property in the configuration object.
    if args.endpoint is not None:
        cfg.endpoint = args.endpoint

    # Initialize the OSS client with the preceding configurations to prepare for interaction with OSS.
    client = oss.Client(cfg)

    # Define the data to be appended.
    data1 = b'hello'
    data2 = b' world. '

    # Append data for the first time.
    with client.append_file(bucket=args.bucket, key=args.key) as f:
        append_f = f
        f.write(data1)
    # Print the file status after the first append operation.
    print(f'closed: {append_f.closed},'
          f' name: {append_f.name}'
    )

    # Append data for the second time.
    with client.append_file(bucket=args.bucket, key=args.key) as f:
        append_f = f
        f.write(data2)
    # Print the file status after the second append operation.
    print(f'closed: {append_f.closed},'
          f' name: {append_f.name}'
    )

    # Obtain the content of the object after appending data.
    result = client.get_object(oss.GetObjectRequest(
        bucket=args.bucket,
        key=args.key,
    ))
    # Print the result of obtaining the object.
    print(f'status code: {result.status_code},'
          f' request id: {result.request_id},'
          f' content: {result.body.content.decode("utf-8")}'
    )

# When this script is executed directly, call the main function to start the processing logic.
if __name__ == "__main__":
    main()  # The entry point of the script, where the program flow starts.

Use AppendObject to perform an append upload

import argparse
import alibabacloud_oss_v2 as oss

# Create a command-line argument parser.
parser = argparse.ArgumentParser(description="append object sample")

# Add command-line arguments.
# --region: Specifies the region where the OSS bucket is located.
parser.add_argument('--region', help='The region in which the bucket is located.', required=True)
# --bucket: Specifies the name of the bucket to operate on.
parser.add_argument('--bucket', help='The name of the bucket.', required=True)
# --endpoint: An optional parameter that specifies the domain name used to access the OSS service.
parser.add_argument('--endpoint', help='The domain names that other services can use to access OSS')
# --key: Specifies the key of the object (file) in OSS.
parser.add_argument('--key', help='The name of the object.', required=True)

def main():
    # Parse the command-line arguments.
    args = parser.parse_args()

    # Load the authentication information required for OSS from environment variables.
    credentials_provider = oss.credentials.EnvironmentVariableCredentialsProvider()

    # Create a configuration object using the default configurations provided by the SDK.
    cfg = oss.config.load_default()

    # Set the credential provider to the previously created object.
    cfg.credentials_provider = credentials_provider

    # Set the region for the OSS client based on user input.
    cfg.region = args.region

    # If the user provides a custom endpoint, update the configuration.
    if args.endpoint is not None:
        cfg.endpoint = args.endpoint

    # Create an OSS client instance using the preceding configurations.
    client = oss.Client(cfg)

    # Define the data to be appended.
    data1 = b'hello'
    data2 = b' world'

    # Append data for the first time.
    result = client.append_object(oss.AppendObjectRequest(
        bucket=args.bucket,  # Specify the destination bucket.
        key=args.key,  # Specify the key of the object.
        position=0,  # The starting position for appending, which is initially 0.
        body=data1,  # The data to be appended.
    ))

    # Print the result of the first append operation.
    print(f'status code: {result.status_code},'
          f' request id: {result.request_id},'
          f' version id: {result.version_id},'
          f' hash crc64: {result.hash_crc64},'
          f' next position: {result.next_position},' 
    )

    # Append data for the second time.
    result = client.append_object(oss.AppendObjectRequest(
        bucket=args.bucket,  # Specify the destination bucket.
        key=args.key,  # Specify the key of the object.
        position=result.next_position,  # Start from the next position of the previous append operation.
        body=data2,  # The data to be appended.
    ))

    # Print the result of the second append operation.
    print(f'status code: {result.status_code},'
          f' request id: {result.request_id},'
          f' version id: {result.version_id},'
          f' hash crc64: {result.hash_crc64},'
          f' next position: {result.next_position},'
    )

# When this script is run directly, call the main function.
if __name__ == "__main__":
    main()

Scenarios

Display a progress bar for an append upload

import argparse
import alibabacloud_oss_v2 as oss

# Create a command-line argument parser.
parser = argparse.ArgumentParser(description="append object sample")

# Add command-line arguments.
# --region: Specifies the region where the OSS bucket is located.
parser.add_argument('--region', help='The region in which the bucket is located.', required=True)
# --bucket: Specifies the name of the bucket to operate on.
parser.add_argument('--bucket', help='The name of the bucket.', required=True)
# --endpoint: An optional parameter that specifies the domain name used to access the OSS service.
parser.add_argument('--endpoint', help='The domain names that other services can use to access OSS')
# --key: Specifies the key of the object (file) in OSS.
parser.add_argument('--key', help='The name of the object.', required=True)

def main():
    # Parse the command-line arguments.
    args = parser.parse_args()

    # Load the authentication information required for OSS from environment variables.
    credentials_provider = oss.credentials.EnvironmentVariableCredentialsProvider()

    # Create a configuration object using the default configurations provided by the SDK.
    cfg = oss.config.load_default()

    # Set the credential provider to the previously created object.
    cfg.credentials_provider = credentials_provider

    # Set the region for the OSS client based on user input.
    cfg.region = args.region

    # If the user provides a custom endpoint, update the configuration.
    if args.endpoint is not None:
        cfg.endpoint = args.endpoint

    # Create an OSS client instance using the preceding configurations.
    client = oss.Client(cfg)

    # Define a dictionary variable named progress_state to save the upload progress status. The initial value is 0.
    progress_state = {'saved': 0}
    def _progress_fn(n, written, total):
        # Use a dictionary to store the cumulative number of written bytes to avoid using global variables.
        progress_state['saved'] += n

        # Calculate the current upload percentage. The value is obtained by dividing the number of written bytes by the total number of bytes and rounding down the result.
        rate = int(100 * (float(written) / float(total)))

        # Print the current upload progress. \r indicates returning to the beginning of the line to implement real-time refresh in the command line.
        # end='' indicates no line break, so that the next printout overwrites the current line.
        print(f'\rUpload progress: {rate}% ', end='')

    # Define the data to be appended.
    data1 = b'hello'
    data2 = b' world'

    # Append data for the first time.
    result = client.append_object(oss.AppendObjectRequest(
        bucket=args.bucket,  # Specify the destination bucket.
        key=args.key,  # Specify the key of the object.
        position=0,  # The starting position for appending, which is initially 0.
        body=data1,  # The data to be appended.
        progress_fn=_progress_fn,  # Set the progress callback function.
    ))

    # Print the result of the first append operation.
    print(f'status code: {result.status_code},'
          f' request id: {result.request_id},'
          f' version id: {result.version_id},'
          f' hash crc64: {result.hash_crc64},'
          f' next position: {result.next_position},'
    )

    # Append data for the second time.
    result = client.append_object(oss.AppendObjectRequest(
        bucket=args.bucket,  # Specify the destination bucket.
        key=args.key,  # Specify the key of the object.
        position=result.next_position,  # Start from the next position of the previous append operation.
        body=data2,  # The data to be appended.
        progress_fn=_progress_fn,  # Set the progress callback function.
    ))

    # Print the result of the second append operation.
    print(f'status code: {result.status_code},'
          f' request id: {result.request_id},'
          f' version id: {result.version_id},'
          f' hash crc64: {result.hash_crc64},'
          f' next position: {result.next_position},'
    )

# When this script is run directly, call the main function.
if __name__ == "__main__":
    main()

References