Python virtualenv notes

Python3 virtual environment construction

1. Perface

• Why do we need virtual environment

  Simply put, an individual virtual environment can be used by an individual python project so that every project won’t affect each other and also won’t affect the python system environment.

• Why do we use ‘virtualenv’

  In short, it’s the python official recommendation.

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2. Install virtualenv

PS: My laptop is MacBook, so the following procedure is based on the macbook terminal.

1. Before installing, you should make sure you’ve already installed pip, and then use pip to install env.

   pip3 install virtualenv

2. Check if the installation is successful

   virtualenv –version

3. Create the big virtual environment

   Firstly, you should ‘cd’ to the directory where you wanna create VE(virtual environment)

   virtualenv envname #Here you should give your virtual environment name

   The environment will also install Python setuptools, pip, wheel automatically

4. Activate your environment

   Source bigenvname/bin/activate

5. Extra procedure

   For me, I often use terminal to start the editor, so when you activate the environment, Use ‘cd’ to the directory where you wanna store your code file. And then start jupyter notebook.

   jupyter notebook

   So now you can code in the envname virtual environment.

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3. Install virtualenvwrapper

*Note: Sometimes, we may create more than one VE, and we’d like to swap between the different VE. Hence, we need the command ‘workon’ which is belong to the package virtualenvwrapper.

1. Install VEW.

   pip3 install virtualenvwrapper

2. Configure VEW.

   export WORKON_HOME=’your sub-VE address’

   source /usr/local/bin/virtualenvwrapper.sh // execute the command package

   But what if your address is not the above default address, how could you find it? I faced the same problem before. We can try to uninstall the package ‘virtualenvwrapper’ and it will prompt us all the files address we would delete.

   

3. After configuring all the environment parameters, we s=also need to execute source command to make it work.

   source ~/.bash_profile

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4. Use VEW to create sub-environment

1. create sub-env

   makvirtualenv env01(envname)

   The default address is under the previous export WORKON_HOME=’your sub-VE address’.

2. Query the list of VE

   lsvirtualenv -b

3. query the python pakcages

   lssitepackages

4. exchange the sub-VE

   workon envname

5. Remove sub-VE

   rmvirtualenv envname

6. Install python packages in the sub-VE

   pip install packagename

7. exit the sub-VE

   deactivate

8. How to start VE every time start the PC

   Since you totally exit the VE, you need to reactivate the big VE every time you wanna reenter it.

   cd big VE address

   source bigenvname/bin/activate

   workon sub-VEname