12. 가상 환경 및 패키지

12.1. 소개

파이썬 응용 프로그램은 종종 표준 라이브러리의 일부로 제공되지 않는 패키지와 모듈을 사용합니다. 응용 프로그램에 특정 버전의 라이브러리가 필요할 수 있는데, 응용 프로그램에 특정 버그가 수정된 버전이 필요하거나, 라이브러리 인터페이스의 구식 버전을 사용하여 응용 프로그램을 작성할 수도 있기 때문입니다.

즉, 하나의 파이썬 설치가 모든 응용 프로그램의 요구 사항을 충족시키는 것이 불가능할 수도 있습니다. 응용 프로그램 A에 특정 모듈의 버전 1.0이 필요하지만, 응용 프로그램 B에 버전 2.0이 필요한 경우, 요구 사항이 충돌하고, 버전 1.0 또는 2.0을 설치하면 어느 한 응용 프로그램은 실행할 수 없게 됩니다.

The solution for this problem is to create a virtual environment (often shortened to 《virtualenv》), a self-contained directory tree that contains a Python installation for a particular version of Python, plus a number of additional packages.

Different applications can then use different virtual environments. To resolve the earlier example of conflicting requirements, application A can have its own virtual environment with version 1.0 installed while application B has another virtualenv with version 2.0. If application B requires a library be upgraded to version 3.0, this will not affect application A’s environment.

12.2. 가상 환경 만들기

The script used to create and manage virtual environments is called pyvenv. pyvenv will usually install the most recent version of Python that you have available; the script is also installed with a version number, so if you have multiple versions of Python on your system you can select a specific Python version by running pyvenv-3.4 or whichever version you want.

To create a virtualenv, decide upon a directory where you want to place it and run pyvenv with the directory path:

pyvenv tutorial-env

존재하지 않는다면 tutorial-env 디렉터리를 만들고, 그 안에 파이썬 인터프리터의 사본, 표준 라이브러리 및 다양한 지원 파일이 들어있는 디렉터리들을 만듭니다.

Once you’ve created a virtual environment, you need to activate it.

윈도우에서 이렇게 실행합니다:

tutorial-env/Scripts/activate

Unix 또는 MacOS에서 이렇게 실행합니다:

source tutorial-env/bin/activate

(이 스크립트는 bash 셸을 위해 작성된 것으로, csh 또는 fish 셸을 사용하는 경우에는, 대신 activate.csh 와 activate.fish 스크립트를 사용해야 합니다.)

Activating the virtualenv will change your shell’s prompt to show what virtualenv you’re using, and modify the environment so that running python will get you that particular version and installation of Python. For example:

-> source ~/envs/tutorial-env/bin/activate
(tutorial-env) -> python
Python 3.4.3+ (3.4:c7b9645a6f35+, May 22 2015, 09:31:25)
  ...
>>> import sys
>>> sys.path
['', '/usr/local/lib/python34.zip', ...,
'~/envs/tutorial-env/lib/python3.4/site-packages']
>>>

12.3. pip로 패키지 관리하기

Once you’ve activated a virtual environment, you can install, upgrade, and remove packages using a program called pip. By default pip will install packages from the Python Package Index, <https://pypi.python.org/pypi>. You can browse the Python Package Index by going to it in your web browser, or you can use pip’s limited search feature:

(tutorial-env) -> pip search astronomy
skyfield               - Elegant astronomy for Python
gary                   - Galactic astronomy and gravitational dynamics.
novas                  - The United States Naval Observatory NOVAS astronomy library
astroobs               - Provides astronomy ephemeris to plan telescope observations
PyAstronomy            - A collection of astronomy related tools for Python.
...

pip 는 《search》, 《install》, 《uninstall》, 《freeze》 등 많은 부속 명령을 갖고 있습니다. (pip 에 대한 완전한 문서는 Installing Python Modules 지침을 보면 됩니다.)

You can install the latest version of a package by specifying a package’s name:

-> pip install novas
Collecting novas
  Downloading novas-3.1.1.3.tar.gz (136kB)
Installing collected packages: novas
  Running setup.py install for novas
Successfully installed novas-3.1.1.3

You can also install a specific version of a package by giving the package name followed by == and the version number:

-> pip install requests==2.6.0
Collecting requests==2.6.0
  Using cached requests-2.6.0-py2.py3-none-any.whl
Installing collected packages: requests
Successfully installed requests-2.6.0

If you re-run this command, pip will notice that the requested version is already installed and do nothing. You can supply a different version number to get that version, or you can run pip install --upgrade to upgrade the package to the latest version:

-> pip install --upgrade requests
Collecting requests
Installing collected packages: requests
  Found existing installation: requests 2.6.0
    Uninstalling requests-2.6.0:
      Successfully uninstalled requests-2.6.0
Successfully installed requests-2.7.0

pip uninstall 다음에 하나 이상의 패키지 이름이 오면 가상 환경에서 패키지가 제거됩니다.

pip show will display information about a particular package:

(tutorial-env) -> pip show requests
---
Metadata-Version: 2.0
Name: requests
Version: 2.7.0
Summary: Python HTTP for Humans.
Home-page: http://python-requests.org
Author: Kenneth Reitz
Author-email: me@kennethreitz.com
License: Apache 2.0
Location: /Users/akuchling/envs/tutorial-env/lib/python3.4/site-packages
Requires:

pip list will display all of the packages installed in the virtual environment:

(tutorial-env) -> pip list
novas (3.1.1.3)
numpy (1.9.2)
pip (7.0.3)
requests (2.7.0)
setuptools (16.0)

pip freeze will produce a similar list of the installed packages, but the output uses the format that pip install expects. A common convention is to put this list in a requirements.txt file:

(tutorial-env) -> pip freeze > requirements.txt
(tutorial-env) -> cat requirements.txt
novas==3.1.1.3
numpy==1.9.2
requests==2.7.0

The requirements.txt can then be committed to version control and shipped as part of an application. Users can then install all the necessary packages with install -r:

-> pip install -r requirements.txt
Collecting novas==3.1.1.3 (from -r requirements.txt (line 1))
  ...
Collecting numpy==1.9.2 (from -r requirements.txt (line 2))
  ...
Collecting requests==2.7.0 (from -r requirements.txt (line 3))
  ...
Installing collected packages: novas, numpy, requests
  Running setup.py install for novas
Successfully installed novas-3.1.1.3 numpy-1.9.2 requests-2.7.0

pip 에는 더 많은 옵션이 있습니다. pip 에 대한 완전한 문서는 Installing Python Modules 지침을 참고하세요. 패키지를 작성했을 때 파이썬 패키지 색인에서 사용할 수 있게 하려면, Distributing Python Modules 지침을 참고하세요.