contract_wrappers.py: don't auto-import wrappers

This was discovered while minimizing CircleCI steps to dianose a problem
with running the Launch Kit Backend in CircleCI.

These classes should be imported via the
zero_ex.contract_wrappers.exchange and
zero_ex.contract_wrappers.erc20_token modules, respectively.  We
permitted importing them from just zero_ex.contract_wrappers back when
they were the only wrappers we had, but now that we have so many
different contracts being wrapped, this is just another list to keep
manually updated (which, obviously is error prone, since it slipped
through the cracks already), so it's better to just not support this
type of import.

python-packages/contract_wrappers/src/index.rst

@@ -9,18 +9,18 @@ Python zero_ex.contract_wrappers
    :members:
 
 
-zero_ex.contract_wrappers.Exchange
+zero_ex.contract_wrappers.exchange
 ==================================
 
-.. autoclass:: zero_ex.contract_wrappers.Exchange
+.. automodule:: zero_ex.contract_wrappers.exchange
    :members:
    :special-members:
 
 
-zero_ex.contract_wrappers.ERC20Token
-====================================
+zero_ex.contract_wrappers.erc20_token
+=====================================
 
-.. autoclass:: zero_ex.contract_wrappers.ERC20Token
+.. automodule:: zero_ex.contract_wrappers.erc20_token
    :members:
    :special-members:
 

python-packages/contract_wrappers/src/zero_ex/contract_wrappers/__init__.py

@@ -90,7 +90,7 @@
 we need to tell the WETH token contract to let the 0x contracts transfer our
 balance:
 
->>> from zero_ex.contract_wrappers import ERC20Token
+>>> from zero_ex.contract_wrappers.erc20_token import ERC20Token
 >>> zrx_token = ERC20Token(
 ...     provider=ganache,
 ...     contract_address=NETWORK_TO_ADDRESSES[NetworkId.GANACHE].zrx_token,
@@ -161,7 +161,7 @@
 fill.  This example fills the order completely, but partial fills are possible
 too.
 
->>> from zero_ex.contract_wrappers import Exchange
+>>> from zero_ex.contract_wrappers.exchange import Exchange
 >>> exchange = Exchange(
 ...     provider=ganache,
 ...     contract_address=NETWORK_TO_ADDRESSES[NetworkId.GANACHE].exchange,
@@ -324,5 +324,3 @@
 """
 
 from .tx_params import TxParams
-from .erc20_token import ERC20Token
-from .exchange import Exchange

python-packages/contract_wrappers/test/test_erc20_wrapper.py

@@ -5,7 +5,8 @@
 import pytest
 
 from zero_ex.contract_addresses import NETWORK_TO_ADDRESSES, NetworkId
-from zero_ex.contract_wrappers import ERC20Token, TxParams
+from zero_ex.contract_wrappers import TxParams
+from zero_ex.contract_wrappers.erc20_token import ERC20Token
 
 
 MAX_ALLOWANCE = int("{:.0f}".format(Decimal(2) ** 256 - 1))

python-packages/contract_wrappers/test/test_exchange_wrapper.py

@@ -6,7 +6,8 @@
 from eth_utils import remove_0x_prefix
 
 from zero_ex.contract_addresses import NETWORK_TO_ADDRESSES, NetworkId
-from zero_ex.contract_wrappers import Exchange, TxParams
+from zero_ex.contract_wrappers import TxParams
+from zero_ex.contract_wrappers.exchange import Exchange
 from zero_ex.contract_wrappers.exchange.types import Order
 from zero_ex.json_schemas import assert_valid
 from zero_ex.order_utils import generate_order_hash_hex, sign_hash_to_bytes

python-packages/sra_client/src/zero_ex/sra_client/__init__.py

@@ -315,7 +315,8 @@
 Recall that in a previous example we selected a specific order from the order
 book.  Now let's have the taker fill it:
 
->>> from zero_ex.contract_wrappers import Exchange, TxParams
+>>> from zero_ex.contract_wrappers import TxParams
+>>> from zero_ex.contract_wrappers.exchange import Exchange
 >>> from zero_ex.order_utils import Order
 >>> exchange = Exchange(
 ...     provider=eth_node,