How do you assume an IAM role programmatically inside a Boto3 script?

Call AWS Security Token Service (STS) assume_role to fetch temporary credentials, then initialize a new Boto3 session:

import boto3

sts = boto3.client("sts")

assumed_role = sts.assume_role(
    RoleArn="arn:aws:iam::123456789012:role/TargetDevOpsRole",
    RoleSessionName="AssumedRoleSession"
)

# Extract credentials
creds = assumed_role["Credentials"]

# Create session with temporary credentials
session = boto3.Session(
    aws_access_key_id=creds["AccessKeyId"],
    aws_secret_access_key=creds["SecretAccessKey"],
    aws_session_token=creds["SessionToken"]
)

# Use resources within the context of the assumed role
s3 = session.resource("s3")