Context - Function Compute - Alibaba Cloud Documentation Center

This topic describes context in Python runtimes of Function Compute. This topic also provides an example on how to use context.

What is a context?

When Function Compute runs your function, the system passes a context object to the method that is used to execute the function. The context object contains information about the invocation, service, function, and runtime environment.

The following table describes the parameters that are contained in a context.

Field	Type	Description
request_id	String	The unique ID of the request that is used to invoke the function. You can record the ID for troubleshooting if an error occurs.
credentials	Credentials structure, which contains the following fields: access_key_id access_key_secret security_token	The temporary AccessKey pair that Function Compute obtains by assuming your service-linked role. The temporary AccessKey pair is valid for 36 hours. You can use `credentials` in your code to access related services such as Object Storage Service (OSS). This way, you can access the services without the need to write your AccessKey pair in the function code. For more information, see Grant Function Compute permissions to access other Alibaba Cloud services.
function	FunctionMeta structure, which contains the following fields: name handler memory timeout	The basic information about the invoked function, such as the name, handler, memory, and timeout period of the function.
service	ServiceMeta structure, which contains the following fields: log_project log_store qualifier version_id	The information about the service to which the function belongs, such as the name, the related project, and Logstore in Simple Log Service, the version, and the alias of the service. The `qualifier` parameter indicates the version or alias of the service that is specified when you invoke a function. The `versionId` parameter indicates the version of the service that is actually invoked.
region	String	The ID of the region in which the function is invoked. For example, if the function is invoked in the China (Shanghai) region, the region ID is cn-shanghai. For more information, see Service endpoints.
account_id	String	The ID of the Alibaba Cloud account to which the function belongs.

The following sample code is used as an example to describe the context object.

# -*- coding: utf-8 -*-

import json


class Credentials:
    def __init__(self, access_key_id, access_key_secret, security_token):
        self.access_key_id = access_key_id
        self.access_key_secret = access_key_secret
        self.security_token = security_token


class Tracing:
    def __init__(self, span_context, base64_baggages, jaeger_endpoint):
        self.span_context = span_context
        self.jaeger_endpoint = jaeger_endpoint
        self.span_baggages = self.parseOpenTracingBaggages(base64_baggages)

    def parseOpenTracingBaggages(self, base64_baggages):
        span_baggages = {}
        # None || '' returns false
        if base64_baggages:
            try:
                import base64
                str_baggages = base64.b64decode(base64_baggages)
                span_baggages = json.loads(str_baggages)
            except Exception as e:
                import logging
                fc_sys_logger = logging.getLogger('fc_sys_logger')
                fc_sys_logger.error('Failed to parse base64 opentracing baggages:[{}], err: {}'.format(base64_baggages, e))
        return span_baggages


class FunctionMeta:
    def __init__(self, name, handler, memory, timeout):
        self.name = name
        self.handler = handler
        self.memory = memory
        self.timeout = timeout


class FCContext:
    def __init__(self, account_id, request_id, credentials, function_meta, service_meta, region, tracing):
        self.credentials = credentials
        self.function = function_meta
        self.request_id = request_id
        self.service = service_meta
        self.region = region
        self.account_id = account_id
      # self.tracing = tracing

Example

For an example on context use, see the Example 2: Read and write OSS resources by using a temporary AccessKey pair section in the "Handlers" topic.