This inheritance list is sorted roughly, but not completely, alphabetically:

[detail level 12]

AccountSummaryTags	Class containing all existing values being reported by EClientSocket::reqAccountSummary
Bar	The historical data bar's description
CodeMsgPair	Associates error code and error message as a pair
ComboLeg	Class representing a leg within combo orders
CommissionReport	Class representing the commissions generated by an execution
Contract	Class describing an instrument's definition
ContractCondition
PercentChangeCondition	Used with conditional orders to place or submit an order based on a percentage change of an instrument to the last close price
PriceCondition	Used with conditional orders to cancel or submit order based on price of an instrument
VolumeCondition	Used with conditional orders to submit or cancel an order based on a specified volume change in a security
ContractDetails	Extended contract details
DeltaNeutralContract	Delta-Neutral Contract
EClient	TWS/Gateway client class This client class contains all the available methods to communicate with IB. Up to thirty-two clients can be connected to a single instance of the TWS/Gateway simultaneously. From herein, the TWS/Gateway will be referred to as the Host
EClientSocket	TWS/Gateway client class This client class contains all the available methods to communicate with IB. Up to 32 clients can be connected to a single instance of the TWS/Gateway simultaneously. From herein, the TWS/Gateway will be referred to as the Host
EClientErrors	Contains all possible errors occurring on the client side. This errors are not sent by the TWS but rather generated as the result of malfunction within the TWS API client
EClientMsgSink
EClientSocket	TWS/Gateway client class This client class contains all the available methods to communicate with IB. Up to 32 clients can be connected to a single instance of the TWS/Gateway simultaneously. From herein, the TWS/Gateway will be referred to as the Host
EReader	Captures incoming messages to the API client and places them into a queue
EReaderSignal	Notifies the thread reading information from the TWS whenever there are messages ready to be consumed. Not currently used in Python API
EWrapper	This interface's methods are used by the TWS/Gateway to communicate with the API client. Every API client application needs to implement this interface in order to handle all the events generated by the TWS/Gateway. Almost every EClientSocket method call will result in at least one event delivered here
Execution	Class describing an order's execution
ExecutionFilter	When requesting executions, a filter can be specified to receive only a subset of them
HistoricalTick	The historical tick's description. Used when requesting historical tick data with whatToShow = MIDPOINT
HistoricalTickBidAsk	The historical tick's description. Used when requesting historical tick data with whatToShow = BID_ASK
HistoricalTickLast	The historical last tick's description. Used when requesting historical tick data with whatToShow = TRADES
Liquidity	Class describing the liquidity type of an execution
OperatorCondition
TimeCondition	Time condition used in conditional orders to submit or cancel orders at specified time
Order	The order's description
OrderComboLeg	Allows to specify a price on an order's leg
OrderCondition
ExecutionCondition	This class represents a condition requiring a specific execution event to be fulfilled. Orders can be activated or canceled if a set of given conditions is met. An ExecutionCondition is met whenever a trade occurs on a certain product at the given exchange
OrderState	Provides an active order's current state
ScannerSubscription	Defines a market scanner request
SoftDollarTier	A container for storing Soft Dollar Tier information
TagValue	Convenience class to define key-value pairs
TickAttrib	Tick attributes that describes additional information for price ticks