Python 虚拟环境之virtualenv
1. 介绍¶
为什么要使用虚拟环境？随着你的 Python 项目越来越多，你会发现不同的项目会需要 不同的版本的 Python 库。同一个 Python 库的不同版本可能不兼容。
虚拟环境可以为每一个项目安装独立的 Python 库，这样就可以隔离不同项目之间的 Python 库，也可以隔离项目与操作系统之间的 Python 库。
Python 3 内置了用于创建虚拟环境的 venv 模块。如果你使用的是较新的 Python 版本，那么请接着阅读本文下面的内容。
2 virtualenv¶
2.1 安装¶
# Debian, Ubuntu sudo apt-get install python-virtualenv # CentOS, Fedora sudo yum install python-virtualenv
2.2 帮助¶
root@leco:~/code/env# virtualenv --help
Usage: virtualenv [OPTIONS] DEST_DIR
Options:
--version show program's version number and exit
-h, --help show this help message and exit
-v, --verbose Increase verbosity.
-q, --quiet Decrease verbosity.
-p PYTHON_EXE, --python=PYTHON_EXE
The Python interpreter to use, e.g.,
--python=python3.5 will use the python3.5 interpreter
to create the new environment. The default is the
interpreter that virtualenv was installed with
(/usr/local/bin/python3.6)
--clear Clear out the non-root install and start from scratch.
--no-site-packages DEPRECATED. Retained only for backward compatibility.
Not having access to global site-packages is now the
default behavior.
--system-site-packages
Give the virtual environment access to the global
site-packages.
--always-copy Always copy files rather than symlinking.
--relocatable Make an EXISTING virtualenv environment relocatable.
This fixes up scripts and makes all .pth files
relative.
--no-setuptools Do not install setuptools in the new virtualenv.
--no-pip Do not install pip in the new virtualenv.
--no-wheel Do not install wheel in the new virtualenv.
--extra-search-dir=DIR
Directory to look for setuptools/pip distributions in.
This option can be used multiple times.
--download Download preinstalled packages from PyPI.
--no-download, --never-download
Do not download preinstalled packages from PyPI.
--prompt=PROMPT Provides an alternative prompt prefix for this
environment.
--setuptools DEPRECATED. Retained only for backward compatibility.
This option has no effect.
--distribute DEPRECATED. Retained only for backward compatibility.
This option has no effect.
--unzip-setuptools DEPRECATED. Retained only for backward compatibility.
This option has no effect.
2.3 案例¶
root@leco:~/code/env# ls # 1. 安装Python2的虚拟环境 root@leco:~/code/env# virtualenv -p `which python2` env2 Running virtualenv with interpreter /usr/bin/python2 New python executable in /root/code/env/env2/bin/python2 Also creating executable in /root/code/env/env2/bin/python Installing setuptools, pip, wheel...done. # 2. 安装python3的虚拟环境 root@leco:~/code/env# virtualenv -p `which python3` env3 Running virtualenv with interpreter /usr/local/bin/python3 Using base prefix '/usr/local' New python executable in /root/code/env/env3/bin/python3 Also creating executable in /root/code/env/env3/bin/python Installing setuptools, pip, wheel...done. root@leco:~/code/env# ls env2 env3 # 3. 激活 root@leco:~/code/env# source env3/bin/activate # 4. 安装包[安装后的就在这个当前虚拟环境中] # 激活好虚拟环境，前面会多个虚拟环境的名字 (env3) root@leco:~/code/env# pip install flask Collecting flask Using cached https://files.pythonhosted.org/packages/7f/e7/08578774ed4536d3242b14dacb4696386634607af824ea997202cd0edb4b/Flask-1.0.2-py2.py3-none-any.whl Collecting Jinja2>=2.10 (from flask) Using cached https://files.pythonhosted.org/packages/7f/ff/ae64bacdfc95f27a016a7bed8e8686763ba4d277a78ca76f32659220a731/Jinja2-2.10-py2.py3-none-any.whl Collecting click>=5.1 (from flask) Using cached https://files.pythonhosted.org/packages/fa/37/45185cb5abbc30d7257104c434fe0b07e5a195a6847506c074527aa599ec/Click-7.0-py2.py3-none-any.whl Collecting Werkzeug>=0.14 (from flask) Using cached https://files.pythonhosted.org/packages/20/c4/12e3e56473e52375aa29c4764e70d1b8f3efa6682bef8d0aae04fe335243/Werkzeug-0.14.1-py2.py3-none-any.whl Collecting itsdangerous>=0.24 (from flask) Using cached https://files.pythonhosted.org/packages/76/ae/44b03b253d6fade317f32c24d100b3b35c2239807046a4c953c7b89fa49e/itsdangerous-1.1.0-py2.py3-none-any.whl Collecting MarkupSafe>=0.23 (from Jinja2>=2.10->flask) Downloading https://files.pythonhosted.org/packages/b2/5f/23e0023be6bb885d00ffbefad2942bc51a620328ee910f64abe5a8d18dd1/MarkupSafe-1.1.1-cp36-cp36m-manylinux1_x86_64.whl Installing collected packages: MarkupSafe, Jinja2, click, Werkzeug, itsdangerous, flask Successfully installed Jinja2-2.10 MarkupSafe-1.1.1 Werkzeug-0.14.1 click-7.0 flask-1.0.2 itsdangerous-1.1.0 # 4. 查看当前虚拟环境的安装的包 (env3) root@leco:~/code/env# pip list Package Version ------------ ------- Click 7.0 Flask 1.0.2 itsdangerous 1.1.0 Jinja2 2.10 MarkupSafe 1.1.1 pip 19.0.3 setuptools 40.8.0 Werkzeug 0.14.1 wheel 0.33.1 # 5. 导出安装包 (env3) root@leco:~/code/env# pip list >requirements.txt # 这个文件名随便，默认是这个 有的版本是pip3 freeze > requirements.txt (env3) root@leco:~/code/env# cat requirements.txt Package Version ------------ ------- Click 7.0 Flask 1.0.2 itsdangerous 1.1.0 Jinja2 2.10 MarkupSafe 1.1.1 pip 19.0.3 setuptools 40.8.0 Werkzeug 0.14.1 wheel 0.33.1 这将会创建一个 requirements.txt 文件，其中包含了当前环境中所有包及 各自的版本的简单列表。 可以使用 “pip list”在不产生requirements文件的情况下， 查看已安装包的列表。 # 6. 还原环境， pip install -r requirements.txt # 7. 退出虚拟环境 (env3) root@leco:~/code/env# deactivate root@leco:~/code/env# 退出虚拟环境后，前面虚拟环境名字也消失了。
3. 在外部向程序内部传递参数¶
root@leco:~/code/sys# cat demo1.py import sys print(sys.argv) # 参数列表，返回是列表 print(len(sys.argv)) # 参数个数 print(sys.argv[0]) # 脚本名 print(sys.argv[1]) # 第一个参数 root@leco:~/code/sys# python demo1.py 1 2 ['demo1.py', '1', '2'] 3 demo1.py 1
4. 退出¶
执行到主程序末尾，解释器自动退出，但是如果需要中途退出程序，可以调用sys.exit函数，带有一个可选的整数参数返回给调用它的程序，表示你可以在主程序中捕获对sys.exit的调用。（0是正常退出，其他为异常）
In [1]: import sys
In [2]: sys.exit(0)
An exception has occurred, use %tb to see the full traceback.
SystemExit: 0
/usr/local/lib/python3.6/site-packages/IPython/core/interactiveshell.py:2918: UserWarning: To exit: use 'exit', 'quit', or Ctrl-D.
warn("To exit: use 'exit', 'quit', or Ctrl-D.", stacklevel=1)
In [3]: sys.exit(1)
An exception has occurred, use %tb to see the full traceback.