feat: Add examples/topic_info.py (#812)

Signed-off-by: Aubrey Du <duk110293@gmail.com>

Author: AubreyDDD

CHANGELOG.md

@@ -24,6 +24,7 @@ This changelog is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.
 - Add `examples/token_create_transaction_freeze_key.py` showcasing freeze key behavior, expected failures without the key, and the effect of freezing/unfreezing on transfers.
 - Add `examples/account_info.py` to demonstrate `AccountInfo` opeartions
 - Added `HbarUnit` class and Extend `Hbar` class to handle floating-point numbers
+- Add `examples/topic_info.py` to demonstrate `TopicInfo` operations.
 - feat: Allow `PrivateKey` to be used for keys in `TopicCreateTransaction` for consistency.
 - EvmAddress class
 - `alias`, `staked_account_id`, `staked_node_id` and `decline_staking_reward` fields to AccountCreateTransaction

examples/topic_info.py

@@ -0,0 +1,160 @@
+"""
+**INTERNAL DEVELOPER REFERENCE**
+
+This example is primarily for internal SDK developers and contributors.
+
+---
+
+This example demonstrates how to work with the TopicInfo class.
+
+TopicInfo represents consensus topic information on the Hedera network.
+It exposes attributes such as memo, running hash, sequence number, expiration time,
+admin key, submit key, auto-renewal configuration, and ledger ID.
+
+This example shows:
+- How to manually construct a TopicInfo instance with mock data
+- How to populate key fields
+- How to inspect or pretty-print the data with __str__ / __repr__
+- How to use _from_proto() with a mocked protobuf message
+
+No network calls or topic creation are performed.
+
+Run with:
+    uv run examples/topic_info.py
+    python examples/topic_info.py
+"""
+
+from hiero_sdk_python.consensus.topic_info import TopicInfo
+from hiero_sdk_python.account.account_id import AccountId
+from hiero_sdk_python.crypto.private_key import PrivateKey
+from hiero_sdk_python.Duration import Duration
+from hiero_sdk_python.hapi.services import consensus_topic_info_pb2
+from hiero_sdk_python.hapi.services.basic_types_pb2 import AccountID, Key
+from hiero_sdk_python.hapi.services.timestamp_pb2 import Timestamp
+from hiero_sdk_python.tokens.custom_fixed_fee import CustomFixedFee
+
+def mock_running_hash() -> bytes:
+    """Generate a mock 48-byte running hash."""
+    return bytes.fromhex("00" * 48)
+
+def mock_admin_key() -> Key:
+    """Create a mock admin key."""
+    public_key = PrivateKey.generate_ed25519().public_key()
+    key = Key()
+    key.ed25519 = public_key.to_bytes_raw()
+    return key
+
+def mock_submit_key() -> Key:
+    """Create a mock submit key."""
+    public_key = PrivateKey.generate_ecdsa().public_key()
+    key = Key()
+    key.ECDSA_secp256k1 = public_key.to_bytes_raw()
+    return key
+
+def mock_custom_fee() -> CustomFixedFee:
+    """Create a mock custom fee."""
+    return CustomFixedFee(
+        amount=100,
+        denominating_token_id=None,
+        fee_collector_account_id=AccountId(0, 0, 456),
+        all_collectors_are_exempt=False,
+    )
+
+def mock_expiration_time() -> Timestamp:
+    """Create a mock expiration timestamp."""
+    timestamp = Timestamp()
+    timestamp.seconds = 1767225600
+    timestamp.nanos = 0
+    return timestamp
+
+def mock_auto_renew_account() -> AccountID:
+    """Create a mock auto-renew account ID."""
+    account_id = AccountID()
+    account_id.shardNum = 0
+    account_id.realmNum = 0
+    account_id.accountNum = 100
+    return account_id
+
+def mock_ledger_id() -> bytes:
+    """Create a mock ledger ID."""
+    return bytes.fromhex("01")
+
+def build_mock_topic_info() -> TopicInfo:
+    """Manually construct a TopicInfo instance with mock data."""
+    topic_info = TopicInfo(
+        memo="Example topic memo",
+        running_hash=mock_running_hash(),
+        sequence_number=42,
+        expiration_time=mock_expiration_time(),
+        admin_key=mock_admin_key(),
+        submit_key=mock_submit_key(),
+        auto_renew_period=Duration(7776000),
+        auto_renew_account=mock_auto_renew_account(),
+        ledger_id=mock_ledger_id(),
+        fee_schedule_key=None,
+        fee_exempt_keys=None,
+        custom_fees=[mock_custom_fee()],
+    )
+    return topic_info
+
+def build_topic_info_from_proto() -> TopicInfo:
+    """Build a TopicInfo from a mocked protobuf message using _from_proto()."""
+    proto = consensus_topic_info_pb2.ConsensusTopicInfo()
+    proto.memo = "Topic from protobuf"
+    proto.runningHash = mock_running_hash()
+    proto.sequenceNumber = 100
+    proto.expirationTime.CopyFrom(mock_expiration_time())
+    proto.adminKey.CopyFrom(mock_admin_key())
+    proto.submitKey.CopyFrom(mock_submit_key())
+    proto.autoRenewPeriod.seconds = 7776000
+    proto.autoRenewAccount.CopyFrom(mock_auto_renew_account())
+    proto.ledger_id = mock_ledger_id()
+    proto.custom_fees.append(mock_custom_fee()._to_topic_fee_proto())
+    
+    topic_info = TopicInfo._from_proto(proto)
+    return topic_info
+
+def print_topic_info(topic: TopicInfo) -> None:
+    """Display the key attributes of a TopicInfo instance."""
+    print("\nTopicInfo Details:")
+    print(f"  Memo: {topic.memo}")
+    print(f"  Sequence Number: {topic.sequence_number}")
+    print(f"  Running Hash: {topic.running_hash.hex()}")
+    
+    if topic.auto_renew_period:
+        print(f"  Auto-Renew Period: {topic.auto_renew_period.seconds} seconds")
+    
+    if topic.ledger_id:
+        print(f"  Ledger ID: {topic.ledger_id.hex()}")
+    
+    print(f"  Custom Fees: {len(topic.custom_fees)}")
+    
+    # Pretty-print using __str__
+    print("\nUsing __str__:")
+    print(topic)
+    
+    # Pretty-print using __repr__
+    print("\nUsing __repr__:")
+    print(repr(topic))
+
+def main():
+    """Demonstrate TopicInfo functionality."""
+    print("TopicInfo Example - Demonstrating topic info construction and inspection")
+    print("=" * 70)
+    
+    # Build TopicInfo directly
+    print("\n1. Building TopicInfo directly:")
+    topic1 = build_mock_topic_info()
+    print_topic_info(topic1)
+    
+    # Build TopicInfo from protobuf
+    print("\n" + "=" * 70)
+    print("\n2. Building TopicInfo from protobuf:")
+    topic2 = build_topic_info_from_proto()
+    print_topic_info(topic2)
+    
+    print("\n" + "=" * 70)
+    print("Example completed successfully!")
+
+if __name__ == "__main__":
+    main()