class_docstr: A Database. Encapsulates a url and an SQLAlchemy engine with a pool of
  connections.
class_docstr_tok: ["A","Database",".","Encapsulates","a","url","and","an","SQLAlchemy","engine","with","a","pool","of","connections","."]
docstr: A context manager for executing a transaction on this Database.
docstr_tok: ["A","context","manager","for","executing","a","transaction","on","this","Database","."]
code: def transaction(self):
      """A context manager for executing a transaction on this Database."""
  
      conn = self.get_connection()
      tx = conn.transaction()
      try:
          yield conn
          tx.commit()
      except:
          tx.rollback()
      finally:
          conn.close()
  
imports: import os
  from sys import stdout
  from collections import OrderedDict
  from contextlib import contextmanager
  from inspect import isclass
  import tablib
  from docopt import docopt
  from sqlalchemy import create_engine, exc, inspect, text
label_desc: Use image node_id 12 for calling the Database obj's underlying member method code with example usage: obj.transaction() without return types