[python] Introduce db List in Python CLI

Author: JingsongLi

docs/content/pypaimon/cli.md

@@ -431,6 +431,21 @@ paimon db alter mydb --remove key1 key2
 paimon db alter mydb --set '{"key1": "new_value"}' --remove key2
 ```
 
+### DB List
+
+List all databases in the catalog.
+
+```shell
+paimon db list
+```
+
+Output:
+```
+default
+mydb
+analytics
+```
+
 ### DB List Tables
 
 List all tables in a database.

paimon-python/pypaimon/catalog/catalog.py

@@ -39,6 +39,10 @@ class Catalog(ABC):
     COMMENT_PROP = "comment"
     OWNER_PROP = "owner"
 
+    @abstractmethod
+    def list_databases(self) -> List[str]:
+        """List all database names in the catalog."""
+
     @abstractmethod
     def get_database(self, name: str) -> 'Database':
         """Get paimon database identified by the given name."""

paimon-python/pypaimon/catalog/filesystem_catalog.py

@@ -48,6 +48,17 @@ def __init__(self, catalog_options: Options):
         self.catalog_options = catalog_options
         self.file_io = FileIO.get(self.warehouse, self.catalog_options)
 
+    def list_databases(self) -> list:
+        statuses = self.file_io.list_status(self.warehouse)
+        database_names = []
+        for status in statuses:
+            import pyarrow.fs as pafs
+            is_directory = hasattr(status, 'type') and status.type == pafs.FileType.Directory
+            name = status.base_name if hasattr(status, 'base_name') else ""
+            if is_directory and name and name.endswith(Catalog.DB_SUFFIX):
+                database_names.append(name[:-len(Catalog.DB_SUFFIX)])
+        return sorted(database_names)
+
     def get_database(self, name: str) -> Database:
         if self.file_io.exists(self.get_database_path(name)):
             return Database(name, {})

paimon-python/pypaimon/cli/cli_db.py

@@ -169,6 +169,32 @@ def cmd_db_alter(args):
         sys.exit(1)
 
 
+def cmd_db_list(args):
+    """
+    Execute the 'db list' command.
+
+    Lists all databases in the catalog.
+
+    Args:
+        args: Parsed command line arguments.
+    """
+    from pypaimon.cli.cli import load_catalog_config, create_catalog
+
+    config = load_catalog_config(args.config)
+    catalog = create_catalog(config)
+
+    try:
+        databases = catalog.list_databases()
+    except Exception as e:
+        print(f"Error: Failed to list databases: {e}", file=sys.stderr)
+        sys.exit(1)
+
+    if not databases:
+        print("No databases found.")
+    else:
+        for database_name in databases:
+            print(database_name)
+
 def cmd_db_list_tables(args):
     """
     Execute the 'db list-tables' command.
@@ -270,6 +296,10 @@ def add_db_subcommands(db_parser):
     )
     alter_parser.set_defaults(func=cmd_db_alter)
 
+    # db list command
+    list_parser = db_subparsers.add_parser('list', help='List all databases')
+    list_parser.set_defaults(func=cmd_db_list)
+
     # db list-tables command
     list_tables_parser = db_subparsers.add_parser('list-tables', help='List all tables in a database')
     list_tables_parser.add_argument(

paimon-python/pypaimon/tests/cli_db_test.py

@@ -300,6 +300,39 @@ def test_cli_db_alter_invalid_json(self):
                 error_output = mock_stderr.getvalue()
                 self.assertIn('Invalid JSON', error_output)
 
+    def test_cli_db_list_basic(self):
+        """Test basic list databases via CLI."""
+        self.catalog.create_database('list_db_a', True)
+        self.catalog.create_database('list_db_b', True)
+
+        with patch('sys.argv',
+                   ['paimon', '-c', self.config_file, 'db', 'list']):
+            with patch('sys.stdout', new_callable=StringIO) as mock_stdout:
+                try:
+                    main()
+                except SystemExit:
+                    pass
+
+                output = mock_stdout.getvalue()
+                self.assertIn('list_db_a', output)
+                self.assertIn('list_db_b', output)
+
+    def test_cli_db_list_excludes_nonexistent(self):
+        """Test list databases does not include non-existent databases."""
+        self.catalog.create_database('list_exists_db', True)
+
+        with patch('sys.argv',
+                   ['paimon', '-c', self.config_file, 'db', 'list']):
+            with patch('sys.stdout', new_callable=StringIO) as mock_stdout:
+                try:
+                    main()
+                except SystemExit:
+                    pass
+
+                output = mock_stdout.getvalue()
+                self.assertIn('list_exists_db', output)
+                self.assertNotIn('never_created_db', output)
+
 
 if __name__ == '__main__':
     unittest.main()