Python也可以编写智能合约：从NEO开始

NEO是一个非盈利的社区化的区块链项目，是利用区块链技术和数字身份进行资产数字化，利用智能合约对数字资产进行自动化管理，实现“智能经济”的一种分布式网络，被称为“中国以太坊”。本文将带领大家学习如何使用Python编写NEO智能合约。

环境搭建
基于macOS或Ubuntu，windows用户请自备虚拟机。
安装Docker及拉取镜像
macOS:
1.点我去下载，下载后安装并启动，启动成功后任务栏会有个Docker的图标，点击可以查看运行状态

2.拉取私链镜像，打开终端执行
docker pull cityofzion/neo-privatenet

Tip：由于国内环境问题，docker镜像的拉取往往会非常慢，所以我们可以配置一些国内的镜像加速，如DaoCloud的Docker 加速器，免费注册一下，按照说明配置即可，非常简单和方便。
3.运行Docker容器，执行
Ubuntu:
1.安装Docker，执行
sudo apt install docker.io
2.启动Docker，执行(安装成功后应该会默认已启动)
sudo service docker start
3.拉取私有链网络镜像，执行
sudo docker pull cityofzion/neo-privatenet
4.运行docker容器，执行
sudo docker run --rm -d --name neo-privatenet -p 20333-20336:20333-20336/tcp -p 30333-30336:30333-30336/tcp cityofzion/neo-privatenet
安装Python3和levelDB
macOS:
没有安装过Homebrew的请先执行下面的命令，已安装的忽略。
/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
1.macOS是自带Python2的，我们需要安装Python3
brew install python3
2.安装levelDB
brew install leveldb
Ubuntu:
简单粗暴的依次执行下面命令：
sudo apt install software-properties-common python-software-properties
sudo add-apt-repository ppa:deadsnakes/ppa
sudo apt update
sudo apt install python3.6 python3.6-dev python3.6-venv python3-pip libleveldb-dev libssl-dev g++
Tip：因为NEO最低需要Python3.6的环境，Homebrew是会安装最新版本的Python，而apt-get源上直接install python3安装的是python3.5，所以这里我们指定的python3.6。
neo-python
从GitHub克隆neo-python项目
git clone https://github.com/CityOfZion/neo-python.git
创建并进入虚拟环境
cd neo-python
python3 -m venv venv # 创建虚拟环境，Ubuntu这里使用 python3.6 -m venv venv
source venv/bin/activate # 进入虚拟环境，退出虚拟环境使用命令 deactivate
安装依赖包
pip install -r requirements.txt
pip install -e .
启动连接到私有链网络，进入NEO cli命令行
np-prompt -p # 退出命令行在命令行输入 quit

出现如下界面进入了NEO命令行，那么恭喜你已经成功搭建好所有环境，如果你报错了，请接着往下看。
np-prompt -p 可能出现的错误
错误一

Traceback (most recent call last):
  File "/home/parallels/Code/neosc/neo-python/venv/bin/np-prompt", line 11, in
load_entry_point('neo-python', 'console_scripts', 'np-prompt')()
  File "/home/parallels/Code/neosc/neo-python/venv/lib/python3.6/site-packages/pkg_resources/__init__.py", line 480, in load_entry_point
return get_distribution(dist).load_entry_point(group, name)
  File "/home/parallels/Code/neosc/neo-python/venv/lib/python3.6/site-packages/pkg_resources/__init__.py", line 2693, in load_entry_point
return ep.load()
  File "/home/parallels/Code/neosc/neo-python/venv/lib/python3.6/site-packages/pkg_resources/__init__.py", line 2324, in load
return self.resolve()
  File "/home/parallels/Code/neosc/neo-python/venv/lib/python3.6/site-packages/pkg_resources/__init__.py", line 2330, in resolve
module = __import__(self.module_name, fromlist=['__name__'], level=0)
  File "/home/parallels/Code/neosc/neo-python/neo/bin/prompt.py", line 28, in
from neo.Implementations.Wallets.peewee.UserWallet import UserWallet
  File "/home/parallels/Code/neosc/neo-python/neo/Implementations/Wallets/peewee/UserWallet.py", line 8, in
from neo.Wallets.Wallet import Wallet
  File "/home/parallels/Code/neosc/neo-python/neo/Wallets/Wallet.py", line 13, in
from Crypto.Cipher import AES
  File "/home/parallels/Code/neosc/neo-python/venv/lib/python3.6/site-packages/Crypto/Cipher/__init__.py", line 3, in
from Crypto.Cipher._mode_ecb import _create_ecb_cipher
  File "/home/parallels/Code/neosc/neo-python/venv/lib/python3.6/site-packages/Crypto/Cipher/_mode_ecb.py", line 29, in
from Crypto.Util._raw_api import (load_pycryptodome_raw_lib,
  File "/home/parallels/Code/neosc/neo-python/venv/lib/python3.6/site-packages/Crypto/Util/_raw_api.py", line 32, in
from Crypto.Util.py3compat import byte_string
ImportError: cannot import name 'byte_string'
这是因为依赖包的版本问题，解决方案如下
# 卸载依赖包
pip uninstall pycrypto
pip uninstall pycryptodemo
# 重新安装依赖包
pip install pycrypto
pip install pycryptodemo
pip install -e .
错误二
......
Traceback (most recent call last):
  File "/home/parallels/Code/neosc/neo-python/venv/bin/np-prompt", line 11, in
load_entry_point('neo-python', 'console_scripts', 'np-prompt')()
  File "/home/parallels/Code/neosc/neo-python/neo/bin/prompt.py", line 1061, in main
settings.setup_privnet(args.privnet)
  File "/home/parallels/Code/neosc/neo-python/neo/Settings.py", line 228, in setup_privnet
self.check_privatenet()
  File "/home/parallels/Code/neosc/neo-python/neo/Settings.py", line 314, in check_privatenet
version = client.get_version()
  File "/home/parallels/Code/neosc/neo-python/venv/lib/python3.6/site-packages/neorpc/Client.py", line 283, in get_version
return self._call_endpoint(GET_VERSION, id=id, endpoint=endpoint)
  File "/home/parallels/Code/neosc/neo-python/venv/lib/python3.6/site-packages/neorpc/Client.py", line 310, in _call_endpoint
raise NEORPCException("Could not call method %s with endpoint: %s : %s " % (method, endpoint.addr, e))
neorpc.Client.NEORPCException: Could not call method getversion with endpoint: http://127.0.0.1:30333 : HTTPConnectionPool(host='127.0.0.1', port=30333): Max retries exceeded with url: / (Caused by NewConnectionError(': Failed to establish a new connection: [Errno 111] Connection refused',))
说明你没有启动docker容器并进行端口映射，请看第一部分安装Docker及拉取镜像

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