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this guide discusses how to install packages using and a virtual environment manager: either for python 3 or for python 2. these are the lowest-level tools for managing python packages and are recommended if higher-level tools do not suit your needs.
note
this doc uses the term package to refer to a distribution package which is different from a import package that which is used to import modules in your python source code.
is the reference python package manager. it’s used to install and update packages. you’ll need to make sure you have the latest version of pip installed.
the python installers for windows include pip. you should be able to access pip using:
我要评论py -m pip --version
pip 9.0.1 from c:\python36\lib\site-packages (python 3.6.1)
you can make sure that pip is up-to-date by running:
py -m pip install --upgrade pip
debian and most other distributions include a package, if you want to use the linux distribution-provided versions of pip see installing pip/setuptools/wheel with linux package managers.
you can also install pip yourself to ensure you have the latest version. it’s recommended to use the system pip to bootstrap a user installation of pip:
python3 -m pip install --user --upgrade pip
afterwards, you should have the newest pip installed in your user site:
python3 -m pip --version
pip 9.0.1 from $home/.local/lib/python3.6/site-packages (python 3.6)
note
if you are using python 3.3 or newer, the venv module is the preferred way to create and manage virtual environments. venv is included in the python standard library and requires no additional installation. if you are using venv, you may skip this section.
is used to manage python packages for different projects. using virtualenv allows you to avoid installing python packages globally which could break system tools or other projects. you can install virtualenv using pip.
on macos and linux:
python3 -m pip install --user virtualenv
on windows:
py -m pip install --user virtualenv
(for python 3) and (for python 2) allow you to manage separate package installations for different projects. they essentially allow you to create a “virtual” isolated python installation and install packages into that virtual installation. when you switch projects, you can simply create a new virtual environment and not have to worry about breaking the packages installed in the other environments. it is always recommended to use a virtual environment while developing python applications.
to create a virtual environment, go to your project’s directory and run venv. if you are using python 2, replace venv with virtualenv in the below commands.
on macos and linux:
python3 -m venv env
on windows:
py -m venv env
the second argument is the location to create the virtual environment. generally, you can just create this in your project and call it env.
venv will create a virtual python installation in the env folder.
note
you should exclude your virtual environment directory from your version control system using .gitignore or similar.
before you can start installing or using packages in your virtual environment you’ll need to activate it. activating a virtual environment will put the virtual environment-specific python and pip executables into your shell’s path.
on macos and linux:
source env/bin/activate
on windows:
.\env\scripts\activate
you can confirm you’re in the virtual environment by checking the location of your python interpreter, it should point to the env directory.
on macos and linux:
which python
.../env/bin/python
on windows:
where python
.../env/bin/python.exe
as long as your virtual environment is activated pip will install packages into that specific environment and you’ll be able to import and use packages in your python application.
if you want to switch projects or otherwise leave your virtual environment, simply run:
deactivate
if you want to re-enter the virtual environment just follow the same instructions above about activating a virtual environment. there’s no need to re-create the virtual environment.
now that you’re in your virtual environment you can install packages. let’s install the requests library from the python package index (pypi):
pip install requests
pip should download requests and all of its dependencies and install them:
collecting requests
using cached requests-2.18.4-py2.py3-none-any.whl
collecting chardet<3.1.0,>=3.0.2 (from requests)
using cached chardet-3.0.4-py2.py3-none-any.whl
collecting urllib3<1.23,>=1.21.1 (from requests)
using cached urllib3-1.22-py2.py3-none-any.whl
collecting certifi>=2017.4.17 (from requests)
using cached certifi-2017.7.27.1-py2.py3-none-any.whl
collecting idna<2.7,>=2.5 (from requests)
using cached idna-2.6-py2.py3-none-any.whl
installing collected packages: chardet, urllib3, certifi, idna, requests
successfully installed certifi-2017.7.27.1 chardet-3.0.4 idna-2.6 requests-2.18.4 urllib3-1.22
pip allows you to specify which version of a package to install using . for example, to install a specific version of requests:
pip install requests==2.18.4
to install the latest 2.x release of requests:
pip install requests>=2.0.0,<3.0.0
to install pre-release versions of packages, use the --pre flag:
pip install --pre requests
some packages have optional . you can tell pip to install these by specifying the extra in brackets:
pip install requests[security]
pip can install a package directly from source, for example:
cd google-auth
pip install .
additionally, pip can install packages from source in , meaning that changes to the source directory will immediately affect the installed package without needing to re-install:
pip install --editable .
pip can install packages directly from their version control system. for example, you can install directly from a git repository:
git+https://github.com/googlecloudplatform/google-auth-library-python.git#egg=google-auth
for more information on supported version control systems and syntax, see pip’s documentation on vcs support.
if you have a local copy of a distribution package’s archive (a zip, wheel, or tar file) you can install it directly with pip:
pip install requests-2.18.4.tar.gz
if you have a directory containing archives of multiple packages, you can tell pip to look for packages there and not to use the python package index (pypi) at all:
pip install --no-index --find-links=/local/dir/ requests
this is useful if you are installing packages on a system with limited connectivity or if you want to strictly control the origin of distribution packages.
if you want to download packages from a different index than the python package index (pypi), you can use the --index-url flag:
pip install --index-url http://index.example.com/simple/ someproject
if you want to allow packages from both the python package index (pypi) and a separate index, you can use the --extra-index-url flag instead:
pip install --extra-index-url http://index.example.com/simple/ someproject
pip can upgrade packages in-place using the --upgrade flag. for example, to install the latest version of requests and all of its dependencies:
pip install --upgrade requests
instead of installing packages individually, pip allows you to declare all dependencies in a requirements file. for example you could create a requirements.txt file containing:
requests==2.18.4
google-auth==1.1.0
and tell pip to install all of the packages in this file using the -r flag:
pip install -r requirements.txt
pip can export a list of all installed packages and their versions using the freeze command:
pip freeze
which will output a list of package specifiers such as:
cachetools==2.0.1
certifi==2017.7.27.1
chardet==3.0.4
google-auth==1.1.1
idna==2.6
pyasn1==0.3.6
pyasn1-modules==0.1.4
requests==2.18.4
rsa==3.4.2
six==1.11.0
urllib3==1.22
this is useful for creating requirements files that can re-create the exact versions of all packages installed in an environment.
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