1、安装虚拟环境

我用的是mac下的python3.6，在命令窗口用：

 ~ pip3 install virtualenv
Collecting virtualenv
  Downloading virtualenv-15.1.0-py2.py3-none-any.whl (1.8MB)
    100% |████████████████████████████████| 1.8MB 650kB/s
Installing collected packages: virtualenv
Successfully installed virtualenv-15.1.0

即可自动安装，当然如果你没有pip模块，则需要先安装pip，网上有很多pip安装教程，例如http://www.cnblogs.com/zdz8207/p/python_learn_note_16.html

安装完虚拟环境，则要开始使用了，在你的项目文件的目录执行：

cd /Users/zhangmeiyuan/PycharmProjects/MyProject 
➜  MyProject ls
TEST     [test1.py](http://test1.py) 
➜  MyProject virtualenv venv
Using base prefix '/Library/Frameworks/Python.framework/Versions/3.6'
New python executable in /Users/zhangmeiyuan/PycharmProjects/MyProject/venv/bin/python3.6
Also creating executable in /Users/zhangmeiyuan/PycharmProjects/MyProject/venv/bin/python

Installing setuptools, pip, wheel...done.

python3在WIN和MAC上自带pyvenv，不用额外安装。
mac：操作如下即可

mkdir .pyvenv
cd .pyvenv
pyvenv flask_venv

2、激活虚拟环境

zhangmeiyuan-5:.pyvenv zhangmeiyuan$ source flask_venv/bin/activate

3、安装Opencv过程及遇到问题解决

接下来就可以在虚拟环境中安装包，不影响外面的环境

问题一、pip版本未升级导致无法进行安装

然后尝试用pip命令进行安装

pip3 install opencv3

也报错了，报错信息如下：

Collecting opencv3
  Could not find a version that satisfies the requirement opencv3 (from versions: )
No matching distribution found for opencv3
You are using pip version 9.0.1, however version 10.0.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
(flask_venv) zhangmeiyuan-5:.pyvenv zhangmeiyuan$ pip3 install --upgrade pip3
Collecting pip3
  Could not find a version that satisfies the requirement pip3 (from versions: )
No matching distribution found for pip3
You are using pip version 9.0.1, however version 10.0.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.

原来是pip需要升级到更新版本,然后更新升级解决。

 pip install --upgrade pip
Collecting pip
  Downloading https://files.pythonhosted.org/packages/0f/74/ecd13431bcc456ed390b44c8a6e917c1820365cbebcb6a8974d1cd045ab4/pip-10.0.1-py2.py3-none-any.whl (1.3MB)
    100% |████████████████████████████████| 1.3MB 470kB/s 
Installing collected packages: pip
  Found existing installation: pip 9.0.1
    Uninstalling pip-9.0.1:
      Successfully uninstalled pip-9.0.1
Successfully installed pip-10.0.1

问题二、通过pip命令无法匹配opencv3安装包版本

但是仍然不能用pip进行opencv的安装
依旧报错

.pyvenv zhangmeiyuan$ pip3 install opencv3
Collecting opencv3
  Could not find a version that satisfies the requirement opencv3 (from versions: )
No matching distribution found for opencv3

问题三：brew 版本问题导致安装不成功

既然pip无法安装，则使用brew命令进行安装，直接输入命令

brew install opencv3 --with-python3 

报错信息如下：

Error: Could not link:
/usr/local/share/man/man1/brew.1

Please delete these paths and run `brew update`.
Error: Could not link:
/usr/local/share/doc/homebrew

Please delete these paths and run `brew update`.
Error: Xcode alone is not sufficient on El Capitan.
Install the Command Line Tools:
  xcode-select --install

重新安装brew，解决brew版本问题

怀疑是之前安装的brew有问题
用ruby重新安装如下：

.pyvenv zhangmeiyuan$ ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)" 

安装成功
然后再重新执行

 brew install opencv

如果没有报错，说明安装成功了。

4、关联python3和opencv

接着看，我们下面的任务就是正确地使python3和opencv关联起来。注意到我们上面使用homebrew安装了程序，homebrew安装的程序位置都在 /usr/local/Cellar/ 下面，所以我们需要找到的就是opencv的cv2*.so文件，，最终我的so文件位置为：

/usr/local/Cellar/opencv3/3.1.0_4/lib/python3.5/site-packages/cv2.cpython-35m-darwin.so

下面就是和python3环境关联，还有和虚拟virtualenv开发环境关联。
我关联的是虚拟环境，只要转到python3 的site-packages文件夹下面和原来上面的so建立一个软链接就行。

cd /usr/local/lib/python3.5/site-packages  
ln -s /usr/local/Cellar/opencv3/3.1.0_4/lib/python3.5/site-packages/cv2.cpython-35m-darwin.so cv2.so  

cd /Users/zhangmeiyuan/PycharmProjects/MyProject/venv/lib/python3.6/site-packages
ln -s /usr/local/Cellar/opencv/3.4.1_5/lib/python3.6/site-packages/cv2.cpython-36m-darwin.so cv2.so

激活virtualenv虚拟环境，输入python
然后输入import cv2
后报错如下：

>>> import cv2
RuntimeError: module compiled against API version 0xc but this version of numpy is 0xb
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: numpy.core.multiarray failed to import

看报错信息意思是numpy安装的版本有问题，删除之前安装的numpy文件夹后，再次输入pip install -U numpy，重新下载numpy。

$ pip3 install -U numpy
Collecting numpy
  Downloading https://files.pythonhosted.org/packages/8e/75/7a8b7e3c073562563473f2a61bd53e75d0a1f5e2047e576ee61d44113c22/numpy-1.14.3-cp36-cp36m-macosx_10_6_intel.macosx_10_9_intel.macosx_10_9_x86_64.macosx_10_10_intel.macosx_10_10_x86_64.whl (4.7MB)
    100% |████████████████████████████████| 4.7MB 1.1MB/s 
superset 0.19.1 has requirement cryptography==1.9, but you'll have cryptography 2.1.4 which is incompatible.
superset 0.19.1 has requirement requests==2.17.3, but you'll have requests 2.6.0 which is incompatible.
Installing collected packages: numpy
  Found existing installation: numpy 1.13.1
    Uninstalling numpy-1.13.1:
      Successfully uninstalled numpy-1.13.1
Successfully installed numpy-1.14.3

5、检查是否安装成功

然后重新查看opencv是否真正安装成功。

>>> import cv2
>>> cv2.__version__
'3.4.1'
>>> 

到此为止，mac下的python3 的opencv安装成功。