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How do I "pretend" to install a package using pip?

This feels like such a simple question, but I can't find any reference in the pip documentation and the only question that seemed relevant mentions a flag that has apparently been deprecated since version 1.5 (version 8.1 is current at the time of this writing).
How do I "pretend" to install a package or list of packages using pip, without actually installing them? I have two separate use cases for this:
I need to see what packages out of a long (~70 line) requirements.txt are missing, without actually installing them; seeing what requirements are already satisfied without installing the missing requirements would satisfy this for me.
Finding the dependencies for a package that I have not yet installed on my computer, without using something like Portage or Aptitude.

There is also the pretty useful pip-tools package that provides a pip-sync tool which you can execute in a "dry run" mode against your requirements file(s):
$ mkvirtualenv test_so
New python executable in test_so/bin/python
Installing setuptools, pip, wheel...done.
...
(test_so) $ pip install pip-tools
...
Installing collected packages: six, click, first, pip-tools
(test_so) $ echo "Django==1.6.11" > requirements.txt
(test_so) $ pip-sync --dry-run requirements.txt
Would install:
Django==1.6.11
Also, here is a partially relevant thread: Check if requirements are up to date.

Per the pip documentation, the proper way to generate the requirements.txt file is via pip freeze > requirements.txt. Hopefully this is what you wanted.

Check if requirements are up to date

I'm using pip requirements files for keeping my dependency list.
I also try to follow best practices for managing dependencies and provide precise package versions inside the requirements file. For example:
Django==1.5.1
lxml==3.0
The question is: Is there a way to tell that there are any newer package versions available in the Python Package Index for packages listed inside requirements.txt?
For this particular example, currently latest available versions are 1.6.2 and 3.3.4 for Django and lxml respectively.
I've tried pip install --upgrade -r requirements.txt, but it says that all is up-to-date:
$ pip install --upgrade -r requirements.txt
Requirement already up-to-date: Django==1.5.1 ...
Note that at this point I don't want to run an actual upgrade - I just want to see if there are any updates available.

Pip has this functionality built-in. Assuming that you're inside your virtualenv type:
$ pip list --outdated
psycopg2 (Current: 2.5.1 Latest: 2.5.2)
requests (Current: 2.2.0 Latest: 2.2.1)
$ pip install -U psycopg2 requests
After that new versions of psycopg2 and requests will be downloaded and installed. Then:
$ pip freeze > requirements.txt
And you are done. This is not one command but the advantage is that you don't need any external dependencies.

Just found a python package specifically for the task - piprot, with the following slogan:
How rotten are your requirements?
It's very straightforward to work with:
$ piprot requirements.txt
Django (1.5.1) is 315 days out of date. Latest is 1.6.2
lxml (3.0) is 542 days out of date. Latest is 3.3.4
Your requirements are 857 days out of date
Also you can "pipe" pip freeze to piprot command, so it can actually inspect how rotten are the packages installed in your sandbox/virtual environment:
pip freeze | piprot
Hope that will help somebody in the future.

Since you mentioned you like to follow best practices, I am guessing you are using virtualenv too, correct? Assuming that is the case, and since you are already pinning your packages, there is a tool called pip-tools that you can run against your virtualenv to check for updates.
There is a down side, and why I mentioned the use of virtualenv though.
[the tool] checks PyPI and reports available updates. It uses the list of
currently installed packages to check for updates, it does not use any
requirements.txt
If you run it in your virtualenv, you can easily see which packages have updates available for your current active environment. If you aren't using virtualenv, though, it's probably not best to run it against the system as your other projects may depend on different versions (or may not work well with updated version even if they all currently work).
From the documentation provided, usage is simple. The pip-review shows you what updates are available, but does not install them.
$ pip-review
requests==0.13.4 available (you have 0.13.2)
redis==2.4.13 available (you have 2.4.9)
rq==0.3.2 available (you have 0.3.0)
If you want to automatically install as well, the tool can handle that too: $ pip-review --auto. There is also an --interactive switch that you can use to selectively update packages.
Once all of this is done, pip-tools provides a way to update your requirements.txt with the newest versions: pip-dump. Again, this runs against the currently active environment, so it is recommended for use within a virtualenv.
Installation of the project can be accomplished via pip install pip-tools.
Author's note: I've used this for small Django projects and been very pleased with it. One note, though, if you install pip-tools into your virtual environment, when you run pip-dump you'll find that it gets added to your requirements.txt file. Since my projects are small, I've always just manually removed that line. If you have a build script of some kind, you may want to automatically strip it out before you deploy.

You can just simply do something like this in your env (virtual or non virtual):
pip freeze | cut -d = -f 1 | xargs -n 1 pip search | grep -B2 'LATEST:'

Installing Python packages from local file system folder to virtualenv with pip

Is it possible to install packages using pip from the local filesystem?
I have run python setup.py sdist for my package, which has created the appropriate tar.gz file. This file is stored on my system at /srv/pkg/mypackage/mypackage-0.1.0.tar.gz.
Now in a virtual environment I would like to install packages either coming from pypi or from the specific local location /srv/pkg.
Is this possible?
PS
I know that I can specify pip install /srv/pkg/mypackage/mypackage-0.1.0.tar.gz. That will work, but I am talking about using the /srv/pkg location as another place for pip to search if I typed pip install mypackage.

What about::
pip install --help
...
-e, --editable <path/url> Install a project in editable mode (i.e. setuptools
"develop mode") from a local project path or a VCS url.
eg, pip install -e /srv/pkg
where /srv/pkg is the top-level directory where 'setup.py' can be found.

I am pretty sure that what you are looking for is called --find-links option.
You can do
pip install mypackage --no-index --find-links file:///srv/pkg/mypackage

From the installing-packages page you can simply run:
pip install /srv/pkg/mypackage
where /srv/pkg/mypackage is the directory, containing setup.py.
Additionally1, you can install it from the archive file:
pip install ./mypackage-1.0.4.tar.gz
1
Although noted in the question, due to its popularity, it is also included.

I am installing pyfuzzybut is is not in PyPI; it returns the message: No matching distribution found for pyfuzzy.
I tried the accepted answer
pip install --no-index --find-links=file:///Users/victor/Downloads/pyfuzzy-0.1.0 pyfuzzy
But it does not work either and returns the following error:
Ignoring indexes: https://pypi.python.org/simple
Collecting pyfuzzy
Could not find a version that satisfies the requirement pyfuzzy (from versions: )
No matching distribution found for pyfuzzy
At last , I have found a simple good way there: https://pip.pypa.io/en/latest/reference/pip_install.html
Install a particular source archive file.
$ pip install ./downloads/SomePackage-1.0.4.tar.gz
$ pip install http://my.package.repo/SomePackage-1.0.4.zip
So the following command worked for me:
pip install ../pyfuzzy-0.1.0.tar.gz.
Hope it can help you.

This is the solution that I ended up using:
import pip
def install(package):
# Debugging
# pip.main(["install", "--pre", "--upgrade", "--no-index",
# "--find-links=.", package, "--log-file", "log.txt", "-vv"])
pip.main(["install", "--upgrade", "--no-index", "--find-links=.", package])
if __name__ == "__main__":
install("mypackagename")
raw_input("Press Enter to Exit...\n")
I pieced this together from pip install examples as well as from Rikard's answer on another question. The "--pre" argument lets you install non-production versions. The "--no-index" argument avoids searching the PyPI indexes. The "--find-links=." argument searches in the local folder (this can be relative or absolute). I used the "--log-file", "log.txt", and "-vv" arguments for debugging. The "--upgrade" argument lets you install newer versions over older ones.
I also found a good way to uninstall them. This is useful when you have several different Python environments. It's the same basic format, just using "uninstall" instead of "install", with a safety measure to prevent unintended uninstalls:
import pip
def uninstall(package):
response = raw_input("Uninstall '%s'? [y/n]:\n" % package)
if "y" in response.lower():
# Debugging
# pip.main(["uninstall", package, "-vv"])
pip.main(["uninstall", package])
pass
if __name__ == "__main__":
uninstall("mypackagename")
raw_input("Press Enter to Exit...\n")
The local folder contains these files: install.py, uninstall.py, mypackagename-1.0.zip

An option --find-links does the job and it works from requirements.txt file!
You can put package archives in some folder and take the latest one without changing the requirements file, for example requirements:
.
└───requirements.txt
└───requirements
├───foo_bar-0.1.5-py2.py3-none-any.whl
├───foo_bar-0.1.6-py2.py3-none-any.whl
├───wiz_bang-0.7-py2.py3-none-any.whl
├───wiz_bang-0.8-py2.py3-none-any.whl
├───base.txt
├───local.txt
└───production.txt
Now in requirements/base.txt put:
--find-links=requirements
foo_bar
wiz_bang>=0.8
A neat way to update proprietary packages, just drop new one in the folder
In this way you can install packages from local folder AND pypi with the same single call: pip install -r requirements/production.txt
PS. See my cookiecutter-djangopackage fork to see how to split requirements and use folder based requirements organization.

Assuming you have virtualenv and a requirements.txt file, then you can define inside this file where to get the packages:
# Published pypi packages
PyJWT==1.6.4
email_validator==1.0.3
# Remote GIT repo package, this will install as django-bootstrap-themes
git+https://github.com/marquicus/django-bootstrap-themes#egg=django-bootstrap-themes
# Local GIT repo package, this will install as django-knowledge
git+file:///soft/SANDBOX/python/django/forks/django-knowledge#egg=django-knowledge

To install only from local you need 2 options:
--find-links: where to look for dependencies. There is no need for the file:// prefix mentioned by others.
--no-index: do not look in pypi indexes for missing dependencies (dependencies not installed and not in the --find-links path).
So you could run from any folder the following:
pip install --no-index --find-links /srv/pkg /path/to/mypackage-0.1.0.tar.gz
If your mypackage is setup properly, it will list all its dependencies, and if you used pip download to download the cascade of dependencies (ie dependencies of depencies etc), everything will work.
If you want to use the pypi index if it is accessible, but fallback to local wheels if not, you can remove --no-index and add --retries 0. You will see pip pause for a bit while it is try to check pypi for a missing dependency (one not installed) and when it finds it cannot reach it, will fall back to local. There does not seem to be a way to tell pip to "look for local ones first, then the index".

Having requirements in requirements.txt and egg_dir as a directory
you can build your local cache:
$ pip download -r requirements.txt -d eggs_dir
then, using that "cache" is simple like:
$ pip install -r requirements.txt --find-links=eggs_dir

What you need is --find-links of pip install.
-f, --find-links If a url or path to an html file, then parse for links to archives. If a local path or
file:// url that's a directory, then look for archives in the directory listing.
In my case, after python -m build, tar.gz package (and whl file) are generated in ./dist directory.
pip install --no-index -f ./dist YOUR_PACKAGE_NAME
Any tar.gz python package in ./dist can be installed by this way.
But if your package has dependencies, this command will prompt error.
To solve this, you can either pip install those deps from official pypi source, then add --no-deps like this
pip install --no-index --no-deps -f ./dist YOUR_PACKAGE_NAME
or copy your deps packages to ./dist directory.

I've been trying to achieve something really simple and failed miserably, probably I'm stupid.
Anyway, if you have a script/Dockerfile which download a python package zip file (e.g. from GitHub) and you then want to install it you can use the file:/// prefix to install it as shown in the following example:
$ wget https://example.com/mypackage.zip
$ echo "${MYPACKAGE_MD5} mypackage.zip" | md5sum --check -
$ pip install file:///.mypackage.zip
NOTE: I know you could install the package straight away using pip install https://example.com/mypackage.zip but in my case I wanted to verify the checksum (never paranoid enough) and I failed miserably when trying to use the various options that pip provides/the #md5 fragment.
It's been surprisingly frustrating to do something so simple directly with pip. I just wanted to pass a checksum and have pip verify that the zip was matching before installing it.
I was probably doing something very stupid but in the end I gave up and opted for this. I hope it helps others trying to do something similar.

In my case, it was because this library depended on another local library, which I had not yet installed. Installing the dependency with pip, and then the dependent library, solved the issue.

If you want to install one local package (package A) to be used inside another local project/package (B) this is quite simple. All you need is to CD to (B) and call:
pip install /path/to/package(A)
Of course you will need to first compile the package (A) with:
sudo python3 ./setup.py install
And, each time you change package A, just run again setup.py in package (A) then pip install ... inside the using project/package (B)

Just add directory on pip command
pip install mypackage file:/location/in/disk/mypackagename.filetype

Python package won't upgrade

As part of a deployment procedure, I upload Python source packages (generated with setup.py sdist) to a remote server and install them in a virtualenv using pip install mypackage-1.0.tar.bz2.
This has worked for long time both for new installs and upgrades (specifically, upgrades without a change in the package's version number). For some reason I cannot figure out, since yesterday, it fails to upgrade the packages. No error is reported, the files are just not changed. Now I'm sure I'm doing something differently but I can't explain the change in behaviour.
I can upgrade the package with the -U --no-deps flags, but this technique forces the deployment script to differentiate between first install and upgrades (--no-deps is required as otherwise dependencies would be downloaded each time from pypi).
Any ideas how I can get a single pip command to do installs and upgrades?

pip install package will only be executed with you don't have this package already.
With you want to upgrade the package you'll have to use: pip install -U package

Install a Python package into a different directory using pip?

I know the obvious answer is to use virtualenv and virtualenvwrapper, but for various reasons I can't/don't want to do that.
So how do I modify the command
pip install package_name
to make pip install the package somewhere other than the default site-packages?

The --target switch is the thing you're looking for:
pip install --target=d:\somewhere\other\than\the\default package_name
But you still need to add d:\somewhere\other\than\the\default to PYTHONPATH to actually use them from that location.
-t, --target <dir>
Install packages into <dir>. By default this will not replace existing files/folders in <dir>.
Use --upgrade to replace existing packages in <dir> with new versions.
Upgrade pip if target switch is not available:
On Linux or OS X:
pip install -U pip
On Windows (this works around an issue):
python -m pip install -U pip

Use:
pip install --install-option="--prefix=$PREFIX_PATH" package_name
You might also want to use --ignore-installed to force all dependencies to be reinstalled using this new prefix. You can use --install-option to multiple times to add any of the options you can use with python setup.py install (--prefix is probably what you want, but there are a bunch more options you could use).

Instead of the --target or --install-options options, I have found that setting the PYTHONUSERBASE environment variable works well (from discussion on a bug regarding this very thing):
PYTHONUSERBASE=/path/to/install/to pip install --user
(Or set the PYTHONUSERBASE directory in your environment before running the command, using export PYTHONUSERBASE=/path/to/install/to)
This uses the very useful --user option but tells it to make the bin, lib, share and other directories you'd expect under a custom prefix rather than $HOME/.local.
Then you can add this to your PATH, PYTHONPATH and other variables as you would a normal installation directory.
Note that you may also need to specify the --upgrade and --ignore-installed options if any packages upon which this depends require newer versions to be installed in the PYTHONUSERBASE directory, to override the system-provided versions.
A full example
PYTHONUSERBASE=/opt/mysterypackage-1.0/python-deps pip install --user --upgrade numpy scipy
..to install the scipy and numpy package most recent versions into a directory which you can then include in your PYTHONPATH like so (using bash and for python 2.6 on CentOS 6 for this example):
export PYTHONPATH=/opt/mysterypackage-1.0/python-deps/lib64/python2.6/site-packages:$PYTHONPATH
export PATH=/opt/mysterypackage-1.0/python-deps/bin:$PATH
Using virtualenv is still a better and neater solution!

To pip install a library exactly where I wanted it, I navigated to the location I wanted the directory with the terminal then used
pip install mylibraryName -t .
the logic of which I took from this page: https://cloud.google.com/appengine/docs/python/googlecloudstorageclient/download

Installing a Python package often only includes some pure Python files. If the package includes data, scripts and or executables, these are installed in different directories from the pure Python files.
Assuming your package has no data/scripts/executables, and that you want your Python files to go into /python/packages/package_name (and not some subdirectory a few levels below /python/packages as when using --prefix), you can use the one time command:
pip install --install-option="--install-purelib=/python/packages" package_name
If you want all (or most) of your packages to go there, you can edit your ~/.pip/pip.conf to include:
[install]
install-option=--install-purelib=/python/packages
That way you can't forget about having to specify it again and again.
Any excecutables/data/scripts included in the package will still go to their default places unless you specify addition install options (--prefix/--install-data/--install-scripts, etc., for details look at the custom installation options).

Tested these options with python3.5 and pip 9.0.3:
pip install --target /myfolder [packages]
Installs ALL packages including dependencies under /myfolder. Does not take into account that dependent packages are already installed elsewhere in Python. You will find packages from /myfolder/[package_name]. In case you have multiple Python versions, this doesn't take that into account (no Python version in package folder name).
pip install --prefix /myfolder [packages]
Checks if dependencies are already installed. Will install packages into /myfolder/lib/python3.5/site-packages/[packages]
pip install --root /myfolder [packages]
Checks dependencies like --prefix but install location will be /myfolder/usr/local/lib/python3.5/site-packages/[package_name].
pip install --user [packages]
Will install packages into $HOME:
/home/[USER]/.local/lib/python3.5/site-packages
Python searches automatically from this .local path so you don't need to put it to your PYTHONPATH.
=> In most of the cases --user is the best option to use.
In case home folder can't be used because of some reason then --prefix.

pip3 install "package_name" -t "target_dir"
source - https://pip.pypa.io/en/stable/reference/pip_install/
-t switch = target

Nobody seems to have mentioned the -t option but that the easiest:
pip install -t <direct directory> <package>

pip install packageName -t pathOfDirectory
or
pip install packageName --target pathOfDirectorty

Just add one point to #Ian Bicking's answer:
Using the --user option to specify the installed directory also work if one wants to install some Python package into one's home directory (without sudo user right) on remote server.
E.g.,
pip install --user python-memcached
The command will install the package into one of the directories that listed in your PYTHONPATH.

Newer versions of pip (8 or later) can directly use the --prefix option:
pip install --prefix=$PREFIX_PATH package_name
where $PREFIX_PATH is the installation prefix where lib, bin and other top-level folders are placed.

To add to the already good advice, as I had an issue installing IPython when I didn't have write permissions to /usr/local.
pip uses distutils to do its install and this thread discusses how that can cause a problem as it relies on the sys.prefix setting.
My issue happened when the IPython install tried to write to '/usr/local/share/man/man1' with Permission denied. As the install failed it didn't seem to write the IPython files in the bin directory.
Using "--user" worked and the files were written to ~/.local. Adding ~/.local/bin to the $PATH meant I could use "ipython" from there.
However I'm trying to install this for a number of users and had been given write permission to the /usr/local/lib/python2.7 directory. I created a "bin" directory under there and set directives for distutils:
vim ~/.pydistutils.cfg
[install]
install-data=/usr/local/lib/python2.7
install-scripts=/usr/local/lib/python2.7/bin
then (-I is used to force the install despite previous failures/.local install):
pip install -I ipython
Then I added /usr/local/lib/python2.7/bin to $PATH.
I thought I'd include this in case anyone else has similar issues on a machine they don't have sudo access to.

If you are using brew with python, unfortunately, pip/pip3 ships with very limited options. You do not have --install-option, --target, --user options as mentioned above.
Note on pip install --user
The normal pip install --user is disabled for brewed Python. This is because of a bug in distutils, because Homebrew writes a distutils.cfg which sets the package prefix.
A possible workaround (which puts executable scripts in ~/Library/Python/./bin) is:
python -m pip install --user --install-option="--prefix=" <package-name>
You might find this line very cumbersome. I suggest use pyenv for management.
If you are using
brew upgrade python python3
Ironically you are actually downgrade pip functionality.
(I post this answer, simply because pip in my mac osx does not have --target option, and I have spent hours fixing it)

With pip v1.5.6 on Python v2.7.3 (GNU/Linux), option --root allows to specify a global installation prefix, (apparently) irrespective of specific package's options. Try f.i.,
$ pip install --root=/alternative/prefix/path package_name

I suggest to follow the documentation and create ~/.pip/pip.conf file. Note in the documentation there are missing specified header directory, which leads to following error:
error: install-base or install-platbase supplied, but installation scheme is incomplete
The full working content of conf file is:
[install]
install-base=$HOME
install-purelib=python/lib
install-platlib=python/lib.$PLAT
install-scripts=python/scripts
install-headers=python/include
install-data=python/data
Unfortunatelly I can install, but when try to uninstall pip tells me there is no such package for uninstallation process.... so something is still wrong but the package goes to its predefined location.

pip install /path/to/package/
is now possible.
The difference with this and using the -e or --editable flag is that -e links to where the package is saved (i.e. your downloads folder), rather than installing it into your python path.
This means if you delete/move the package to another folder, you won't be able to use it.

system` option, that will install pip package-bins to /usr/local/bin thats accessible to all users. Installing without this option may not work for all users as things go to user specific dir like $HOME/.local/bin and then it is user specific install which has to be repeated for all users, also there can be path issues if not set for users, then bins won't work. So if you are looking for all users - yu need to have sudo access:
sudo su -
python3 -m pip install --system <module>
logout
log back in
which <module-bin> --> it should be installed on /usr/local/bin/

Sometimes it works only works with Cache argument
-m pip install -U pip --target=C:\xxx\python\lib\site-packages Pillow --cache-dir C:\tmp