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Pip for Python 3.8

How do I install Pip for Python 3.8 ? I made 3.8 my default Python version.
sudo apt install python3.8-pip
gives
unable to locate package python3.8-pip
and running
python3.8 -m pip install [package]
gives
no module named pip
I can't run sudo apt install python3-pip because it installs pip for Python 3.6

Install pip the official way:
curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py
python3.8 get-pip.py
made 3.8 my default Python version
It depends on how you did that, but it might break something in your OS. For example some packages on Ubuntu 18.04 might depend on python being python2.7 or python3 being python3.6 with some pip packages preinstalled.

sudo apt install python3.8
sudo apt install python3.8-distutils
wget https://bootstrap.pypa.io/get-pip.py
sudo python3.8 get-pip.py

If you installed Python3.8 using apt, the pip documentation advises against using the get-pip.py script:
Be cautious if you are using a Python install that is managed by your operating system or another package manager. get-pip.py does not coordinate with those tools, and may leave your system in an inconsistent state.
The same page suggests running:
python3.8 -m pip --version
to determine if pip is already installed. I installed Python 3.8 on an Ubuntu18 machine using apt install python3.8, and I verified with the command above that it includes pip. It appears that Ubuntu package doesn't install a pip command that you can run directly. But you can run it using the python3.8 binary directly instead, anywhere you would have used pip:
python3.8 -m pip install [package]

you can try updating line #1 from /usr/bin/pip3 to #!/usr/bin/python3.8 as below
#!/usr/bin/python3.8
# GENERATED BY DEBIAN
import sys
# Run the main entry point, similarly to how setuptools does it, but because
# we didn't install the actual entry point from setup.py, don't use the
# pkg_resources API.
from pip import main
if __name__ == '__main__':
sys.exit(main())

What I used to install pip according to the current version of default python is:
sudo apt-get install python-pip

"ImportError: cannot import name main" after upgrading to pip 10.0.0 for Python version 2.7.12 - Only one version of Python is installed

I got a message in my terminal while install a software : You are using pip version 8.1.1, however version 10.0.0 is available. You should consider upgrading via the 'pip install --upgrade pip' command.
So I upgraded pip version: $ pip install --upgrade pip
Now I am getting this error:
~$ pip install ipython
Traceback (most recent call last):
File "/usr/bin/pip", line 9, in <module>
from pip import main
ImportError: cannot import name main

TL;DR
The 'ideal' solution (Ubuntu/Debian way):
$ python -m pip uninstall pip to uninstall the new pip 10 and retain your Ubuntu/Debian-provided patched pip 8. For a system-wide installation of modules use apt wherever possible (unless you are in a virtualenv), more on it below. In older Ubuntu/Debian versions, always add --user flag when using pip outside of virtualenvs (installs into ~/.local/, default in python-pip and python3-pip since 2016).
If you still want to use the new pip 10 exclusively, there are 3 quick workarounds:
simply re-open a new bash session (a new terminal tab, or type bash) - and pip 10 becomes available (see pip -V). debian's pip 8 remains installed but is broken; or
$ hash -d pip && pip -V to refresh pip pathname in the $PATH. debian's pip 8 remains installed but is broken; or
$ sudo apt remove python-pip && hash -d pip (for Python 3 it's python3-pip) -- to uninstall debian's pip 8 completely, in favor of your new pip 10.
Note: You will always need to add --user flag to non-debian-provided pip 10, unless you are in a virtualenv! Your use of pip 10 system-wide, outside of virtualenv, is not really supported by Ubuntu/Debian. Never sudo pip!
Details:
https://github.com/pypa/pip/issues/5221#issuecomment-382069604
https://github.com/pypa/pip/issues/5240#issuecomment-381673100
Ubuntu 16.04 with Python 2.7.12
Introduction:
Ironically, despite being suggested by pip itself to do such an upgrade via the pip install --upgrade pip command explicitely in the terminal (ugh!), upgrading it is not recommended in prepackaged GNU/Linux distributions. Ubuntu generally expects using APT package manager for any system-wide Python module updates/installs (including of pip itself), for example:
$ sudo apt-get update (resync Ubuntu package index files from sources)
$ apt-cache search <python-package-name> (full text-search on all available packages)
$ apt-cache show <python-package-name> (displays the package description)
$ sudo apt-get install python-numpy python-scipy python-matplotlib (easily installs heavy modules for data science, resolving all system dependencies automatically)
$ sudo apt-get install ipython (installs the IPython-notebook you were looking for)
$ sudo apt-get install python-pip (installs/upgrades pip to the latest version available in Ubuntu repository – usually slightly behind pypi.org, but it doesn't matter)
If you ever have to use pip install command on Ubuntu/Debian instead of apt-get install, please make sure it runs isolated and does not change the default system-wide Python packages (never use sudo with pip) – more on this below.
ImportError: cannot import name main
The error is caused by the pip install --upgrade pip command: that installs the latest pip version 10 alongside Ubuntu's default pip version from python-pip debian package from the OS distribution (the system Python installation), completely bypassing Ubuntu apt subsystem. It breaks the Ubuntu's default pip: the debian-patched launcher script from python-pip (system-installed to /usr/bin/pip*) tries to do import main() from your newly installed pip 10 library, but with a different import path, so it fails.
This error is discussed in more detail in a developer thread of the pip issue tracker, including a few proposed solutions, such as:
The $ hash -d pip command: when hash is invoked, the full pathname of pip is determined by searching the directories in $PATH and remembered. Any previously-remembered pathname is discarded. The -d option causes the shell to "forget" the remembered location of the given package name; or
Similarly, you can simply re-open a new bash session (a new terminal tab) to refresh pip pathname in $PATH; or
You could just use pip2 command (or pip3 for Python 3) instead of pip to invoke the older system-installed pip script /usr/bin/pip2 , whereas any pip launcher script located in $HOME/.local/bin dir (pip, pip2, pip2.7) will start your new user-installed pip 10 version;
You can also use the versioned Python commands in combination with the -m switch to run the appropriate copy of pip, for example:
$ python2 -m pip install --user SomePackage # default Python 2
$ python2.7 -m pip install --user SomePackage # specifically Python 2.7
That is handy if you have several versions of Python and need an extension from PyPI for a specific Python version. The --user switch is only required when pip is used outside of virtualenv.
Or, uninstall one of the two pips – either user-installed or system-installed – to resolve the conflict:
$ python -m pip uninstall pip – to remove your manually-installed pip in favour of the previously installed Ubuntu-shipped version from python-pip debian package (python3-pip for Python 3); it is slightly older, but it finds and installs latest modules from PyPI just fine, and has a working pip command in the $PATH by default; or
$ sudo apt-get remove python-pip – to uninstall Ubuntu-provided pip in favour of your latest pip 10; if it is not accessible via the short pip command, just add your $HOME/.local/bin directory to your $PATH environment variable to use pip command (see above).
Note: Ubuntu 16.04 pip v8.1.1 and the latest pip v10.0.1 produce exactly the same PyPI index search results and can pull the same module versions;
Finally, you could ignore both pips altogether in favor of APT, and install Python packages system-wide from Ubuntu repo with:
$ apt search <python-package> # e.g. python-pandas
$ apt show <python-package> # e.g. python-flask
$ sudo apt install <python-package>
Packages prefixed with python- are for Python 2; with python3- are for Python 3.
Installation via apt-get may be what you need, in fact, python-packages from Ubuntu repository are preferred whenever possible, particularly in case of heavy system dependencies or when used system-wide. Of course, the amount of Python packages in Ubuntu repository (few thousand!) is relatively smaller compared to PyPI (and have only one version of them), because any OS repository is lagging slightly behind PyPI versions. But the upside of APT is that all the Ubuntu-provided packages underwent integration testing within Ubuntu, plus apt-get quickly resolves heavy dependencies like C extensions automatically. You will always get any required system libraries as part of the apt install, but with pip you have no such guarantees.
APT may not be an option, however, if you really need the latest (or certain older) package version, or when it can only be found at PyPI, or when modules need to be isolated; then pip is indeed more appropriate tool. If you use pip install command on Ubuntu instead of apt-get install, please ensure that it runs in an isolated virtual development environment, such as with virtualenv (sudo apt-get install python-virtualenv), or a built-in venv module (available in python3 only), or at a per-user level (pip install --user command option), but not system-wide (never sudo pip!).
Note: Using sudo pip command (with root access) should be avoided, because it interferes with the operation of the system package manager (apt) and may affect Ubuntu OS components when a system-used python module is unexpectedly upgraded, particularly by dependencies on another pip package. It is advised to never use Pip to change your system-wide Python packages, as these are managed by apt-get on Ubuntu.

I implemmented #catalinpopescu response from ImportError: cannot import name main when running pip --version command in windows7 32 bit
Find pip's path:
$ which pip
Modify file (choose your favorite editor):
$ sudo nano `which pip`
Then modify lines #catalinpopescu said:
Comment/replace lines:
from pip import main
sys.exit(main())
to:
from pip import __main__
sys.exit(__main__._main())
Immediately I upgrade to Pip Version 10.0.1, which appears it hasn't have this error.

try to upgrade the system pip
sudo pip install --upgrade pip
pip install --upgrade pip
this may be useful

Pip command not found in bash - OSX [duplicate]

I downloaded pip and ran python setup.py install and everything worked just fine. The very next step in the tutorial is to run pip install <lib you want> but before it even tries to find anything online I get an error "bash: pip: command not found".
This is on Mac OS X. I'm assuming there's some kind of path setting that was not set correctly when I ran setup.py. How can I investigate further? What do I need to check to get a better idea of the exact cause of the problem?
EDIT: I also tried installing Python 2.7 for Mac in the hopes that the friendly install process would do any housekeeping like editing PATH and whatever else needs to happen for everything to work according to the tutorials, but this didn't work. After installing, running 'python' still ran Python 2.6 and PATH was not updated.

Why not just do sudo easy_install pip or if this is for python 2.6 sudo easy_install-2.6 pip?
This installs pip using the default python package installer system and saves you the hassle of manual set-up all at the same time.
This will allow you to then run the pip command for python package installation as it will be installed with the system python. I also recommend once you have pip using the virtualenv package and pattern. :)

2020 Update:
For current Debian/Ubuntu, use
apt-get install python3-pip
to install pip3.
Old 2013 answer (easy_install is now deprecated):
Use setuptools to install pip: sudo easy_install pip
(I know the above part of my answer is redundant with klobucar's, but I can't add comments yet), so here's an answer with a solution to sudo: easy_install: command not found on Debian/Ubuntu: sudo apt-get install python-setuptools
Also, for python3, use easy_install3 and python3-setuptools.
For Python 3, use apt-get install python3-pip.

First of all: try pip3 instead of pip. Example:
pip3 --version
pip 9.0.1 from /usr/local/lib/python3.6/site-packages (python 3.6)
pip3 should be installed automatically together with Python3.x. The documentation hasn't been updated, so simply replace pip by pip3 in the instructions, when installing Flask for example.
Now, if this doesn't work, you might have to install pip separately.

Update: A more reliable modern way to access the right pip install for the right python install is to use the syntax python -m pip.
Original Answer
pip would install itself into the bin of your python installation location. It also should create a symlink to some more common location like /usr/local/bin/pip
You can either edit your ~/.profile and update your PATH to include /Library/Frameworks/Python.framework/Versions/2.6/bin, or you could create a symlink to it in a place that you know is in your path.
If you do: echo $PATH, you should see the paths currently being searched. If /usr/local/bin is in your PATH, you can do:
ln -s /Library/Frameworks/Python.framework/Versions/2.6/bin/pip /usr/local/bin
I would opt for adding the python bin to your $PATH variable.

I encountered this problem having downloaded python 3.x.x and trying to install awscli - pip: command not found.
Whilst following the instructions for downloading the AWS client, I changed
pip install awscli
to
pip3 install awscli
which ran the correct version.
I've made an alias on my machine to run python3 whilst typing python, which would normally run the system version 2.7. I'm not sure this is a good idea now. I think I'll just type in the commands as they intended them to be.

Check out How to Install Pip article for more information.
As of 2019,
Download get-pip.py provided by https://pip.pypa.io using the following command:
curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py
Run get-pip.py using the following command:
sudo python get-pip.py
After you done installing, run this command to check if pip is installed.
pip --version
Remove get-pip.py file after installing pip.
rm get-pip.py

Install Python latest version as given here
It has many download links like numpy and scipy
Then go to terminal and enter following command:-
sudo easy_install pip
For Python install packages check this
Requirements for Installing Packages
This section describes the steps to follow before installing other Python packages.
Install pip, setuptools, and wheel If you have Python 2 >=2.7.9 or
Python 3 >=3.4 installed from python.org, you will already have pip
and setuptools, but will need to upgrade to the latest version:
On Linux or OS X:
pip install -U pip setuptools On Windows:
python -m pip install -U pip setuptools If you’re using a Python
install on Linux that’s managed by the system package manager (e.g
“yum”, “apt-get” etc…), and you want to use the system package manager
to install or upgrade pip, then see Installing pip/setuptools/wheel
with Linux Package Managers
Otherwise:
Securely Download get-pip.py 1
Run python get-pip.py. 2 This will install or upgrade pip.
Additionally, it will install setuptools and wheel if they’re not
installed already.

I spent ages going through all the answers on this page but found the one that worked for me in the comments of the OP question by s-walsh
The answer is to use pip3:
$ pip3 install <name-of-install>

Installing using apt-get installs a system wide pip, not just a local one for your user. Try this command to get pip running on your system ...
$ sudo apt-get install python-pip python-dev build-essential
Then pip will be installed without any issues and you will be able to use "sudo pip...".

Most of the methods to install PIP are deprecated. Here is the latest (2019) solution. Please download get-pip script
curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py
Run the script
sudo python get-pip.py

Latest update 2021.
In Ubuntu 20 64bit works perfectly
Installation of python3
sudo apt install python3
Pip Installation
sudo apt install python3-pip
Add following alias in $HOME/.bash_aliases in some cases file may be hidden.
alias pip="/usr/bin/python3 -m pip "
Refresh current terminal session.
. ~/.profile
check pip usage: pip
Install a package: pip install {{package_name}}
extra info
to get Home path
echo $HOME
you will get your home path.

To solve:
Add this line to ~/.bash_profile:
export PATH="/usr/local/bin:$PATH"
In a terminal window, run
source ~/.bash_profile

It might be the root permission. I tried exit root login, and use
sudo su -l root
pip <command>

install Homebrew, open Terminal or your favorite OSX terminal emulator and run
$ /usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
insert the Homebrew directory at the top of your PATH environment variable. You can do this by adding the following line at the bottom of your ~/.profile file
export PATH=/usr/local/bin:/usr/local/sbin:$PATH
Now, we can install Python 2.7:
$ brew install python
Get pip repository:
$ git clone https://github.com/pypa/pip
install pip:
$sudo easy_install pip

python install it by default but if not install you can install it manual use following cmd (for linux only )
for python3 :
sudo apt install python3-pip
for python2
sudo apt install python-pip
hope its help.

If you are running Python 3.5, run the following terminal command:
sudo pip3 install -U nltk
Any other pip commands in terminal would be similar:
pip3 install --upgrade pip
sudo pip3 install -U numpy ::

It solved my problem by using
sudo easy_install pip

Solved this by upgrading python 3 brew upgrade python:
Now i can just do:
pip3 install <package>
==> python
Python has been installed as
/usr/local/bin/python3
Unversioned symlinks `python`, `python-config`, `pip` etc. pointing to
`python3`, `python3-config`, `pip3` etc., respectively, have

Based on this stackoverflow answer and some of the answers on this thread, I have created an alias in the rc file:
alias pip="python3 -m pip"
There seem to be many different answers to this question but this seems to be the best-practice approach.

Avoiding sudo:
python <(curl https://bootstrap.pypa.io/get-pip.py) --user
echo 'export "PATH=$HOME/Library/Python/2.7/bin:$PATH"' >> ~/.bash_profile
From:
http://www.pip-command-not-found.com

CentOS 7 users can just use:
yum install python-pip
Also recommend using virtualenv if you're using pip. It can be added in the same way:
yum install python-virtualenv

assuming you have internet see:
https://pip.pypa.io/en/stable/installing/
basically run:
curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py
and
python get-pip.py

Try using this. Instead of zmq, we can use any package instead of zmq.
sudo apt-get install python3-pip
sudo apt-get update
python3 -m pip install zmq
I was was not able to install this zmq package in my docker image because of the same issue i was getting. So tried this as another way to install and it worked fine for me.

To overcome the issue bash: pip: command not found in Mac
Found two versions on Mac 1 is 2.7 and the other is 3.7
when I say sudo easy_install pip, pip got installed under 2.7
when I say sudo easy_install-3.7 pip, pip got installed under 3.7
But, whenever I would require to do pip install , I wanted to install the package under python3.7, so I have set an alias (alias pip=pip3) in .bash_profile.
so now, whenever I do pip install <package_name>, it gets installed under python3.7

(Context: My OS is Amazon linux using AWS. It seems similar to RedHat but it's stripped down a bit, it seems.)
Exit the shell, then open a new shell. The pip command now works.
That's what solved the problem at this location.
You might want to know as well: The pip commands to install software then needed to be written like this example (jupyter for example) to work correctly on my system:
pip install jupyter --user
Specifically, note the lack of sudo, and the presence of --user
Would be real nice if pip docs had said anything about all this, but that would take typing in more characters I guess.

Not sure why this wasnt mentioned before, but the only thing that worked for me (on my NVIDIA Xavier) was:
sudo apt-get install python3-pip
(or sudo apt-get install python-pip for python 2)

apt -y -qq install python3 python3-pip
ln -s /usr/bin/python3 /usr/bin/python
ln -s /usr/bin/pip3 /usr/bin/pip

What I did to overcome this was sudo apt install python-pip.
It turned out my virtual machine did not have pip installed yet. It's conceivable that other people could have this scenario too.

The updated command for installing pip3 is :
sudo apt-get install python3-pip

The problem seems that your python version and the library yoıu want to install is not matching versionally. Ex: If Django is Django3 and your python version is 2.7, you may get this error.
"After installing is running 'python' still ran Python 2.6 and PATH was not updated."
1- Install latest version of Python
2- Change your PATH manually as python38 and compare them.
3- Try to reinstall.
I solved this problem as replacing PATH manually with the latest version of Python.
As for Windows: ;C:\python38\Scripts

how to use python2.7 pip instead of default pip

I just installed python 2.7 and also pip to the 2.7 site package.
When I get the version with:
pip -V
It shows:
pip 1.3.1 from /usr/lib/python2.6/site-packages (python 2.6)
How do I use the 2.7 version of pip located at:
/usr/local/lib/python2.7/site-packages

There should be a binary called "pip2.7" installed at some location included within your $PATH variable.
You can find that out by typing
which pip2.7
This should print something like '/usr/local/bin/pip2.7' to your stdout. If it does not print anything like this, it is not installed. In that case, install it by running
$ wget https://bootstrap.pypa.io/pip/2.7/get-pip.py
$ sudo python2.7 get-pip.py
Now, you should be all set, and
which pip2.7
should return the correct output.

An alternative is to call the pip module by using python2.7, as below:
python2.7 -m pip <commands>
For example, you could run python2.7 -m pip install <package> to install your favorite python modules. Here is a reference: https://stackoverflow.com/a/50017310/4256346.
In case the pip module has not yet been installed for this version of python, you can run the following:
python2.7 -m ensurepip
Running this command will "bootstrap the pip installer". Note that running this may require administrative privileges (i.e. sudo). Here is a reference: https://docs.python.org/2.7/library/ensurepip.html and another reference https://stackoverflow.com/a/46631019/4256346.

as noted here, this is what worked best for me:
sudo apt-get install python3 python3-pip python3-setuptools
sudo update-alternatives --install /usr/bin/python python /usr/bin/python3 10

pip has now dropped support for python2, therefore you can't use python2 pip
You can't find python2-pip in apt-get anymore, and you won't get pip when installing python2 from source
You can still install python modules using apt-get. To install a python prepend ‘python-’ to the module name
apt-get install python-six # install six

How to install python3 version of package via pip on Ubuntu?

I have both python2.7 and python3.2 installed in Ubuntu 12.04.
The symbolic link python links to python2.7.
When I type:
sudo pip install package-name
It will default install python2 version of package-name.
Some package supports both python2 and python3.
How to install python3 version of package-name via pip?

Ubuntu 12.10+ and Fedora 13+ have a package called python3-pip which will install pip-3.2 (or pip-3.3, pip-3.4 or pip3 for newer versions) without needing this jumping through hoops.
I came across this and fixed this without needing the likes of wget or virtualenvs (assuming Ubuntu 12.04):
Install package python3-setuptools: run sudo aptitude install python3-setuptools, this will give you the command easy_install3.
Install pip using Python 3's setuptools: run sudo easy_install3 pip, this will give you the command pip-3.2 like kev's solution.
Install your PyPI packages: run sudo pip-3.2 install <package> (installing python packages into your base system requires root, of course).
…
Profit!

You may want to build a virtualenv of python3, then install packages of python3 after activating the virtualenv. So your system won't be messed up :)
This could be something like:
virtualenv -p /usr/bin/python3 py3env
source py3env/bin/activate
pip install package-name

Short Answer
sudo apt-get install python3-pip
sudo pip3 install MODULE_NAME
Source: Shashank Bharadwaj's comment
Long Answer
The short answer applies only on newer systems. On some versions of Ubuntu the command is pip-3.2:
sudo pip-3.2 install MODULE_NAME
If it doesn't work, this method should work for any Linux distro and supported version:
sudo apt-get install curl
curl https://bootstrap.pypa.io/get-pip.py | sudo python3
sudo pip3 install MODULE_NAME
If you don't have curl, use wget. If you don't have sudo, switch to root. If pip3 symlink does not exists, check for something like pip-3.X
Much python packages require also the dev package, so install it too:
sudo apt-get install python3-dev
Sources:
python installing packages with pip
Pip latest install
Check also Tobu's answer if you want an even more upgraded version of Python.
I want to add that using a virtual environment is usually the preferred way to develop a python application, so #felixyan answer is probably the best in an ideal world. But if you really want to install that package globally, or if need to test / use it frequently without activating a virtual environment, I suppose installing it as a global package is the way to go.

Well, on ubuntu 13.10/14.04, things are a little different.
Install
$ sudo apt-get install python3-pip
Install packages
$ sudo pip3 install packagename
NOT pip-3.3 install

The easiest way to install latest pip2/pip3 and corresponding packages:
curl https://bootstrap.pypa.io/get-pip.py | python2
pip2 install package-name
curl https://bootstrap.pypa.io/get-pip.py | python3
pip3 install package-name
Note: please run these commands as root

I had the same problem while trying to install pylab, and I have found this link
So what I have done to install pylab within Python 3 is:
python3 -m pip install SomePackage
It has worked properly, and as you can see in the link you can do this for every Python version you have, so I guess this solves your problem.

Old question, but none of the answers satisfies me. One of my systems is running Ubuntu 12.04 LTS and for some reason there's no package python3-pip or python-pip for Python 3. So here is what I've done (all commands were executed as root):
Install setuptools for Python3 in case you haven't.
apt-get install python3-setuptools
or
aptitude install python3-setuptools
With Python 2.4+ you can invoke easy_install with specific Python version by using python -m easy_install. So pip for Python 3 could be installed by:
python3 -m easy_install pip
That's it, you got pip for Python 3. Now just invoke pip with the specific version of Python to install package for Python 3. For example, with Python 3.2 installed on my system, I used:
pip-3.2 install [package]

If you have pip installed in both pythons, and both are in your path, just use:
$ pip-2.7 install PACKAGENAME
$ pip-3.2 install PACKAGENAME
References:
http://www.pip-installer.org/docs/pip/en/0.8.3/news.html#id4
https://github.com/pypa/pip/issues/200
This is a duplicate of question #2812520

If your system has python2 as default, use below command to install packages to python3
$ python3 -m pip install <package-name>

Easy enough:
sudo aptitude install python3-pip
pip-3.2 install --user pkg
If you want Python 3.3, which isn't the default as of Ubuntu 12.10:
sudo aptitude install python3-pip python3.3
python3.3 -m pip.runner install --user pkg

You can alternatively just run pip3 install packagename instead of pip,

Firstly, you need to install pip for the Python 3 installation that you want. Then you run that pip to install packages for that Python version.
Since you have both pip and python 3 in /usr/bin, I assume they are both installed with a package manager of some sort. That package manager should also have a Python 3 pip. That's the one you should install.
Felix' recommendation of virtualenv is a good one. If you are only testing, or you are doing development, then you shouldn't install the package in the system python. Using virtualenv, or even building your own Pythons for development, is better in those cases.
But if you actually do want to install this package in the system python, installing pip for Python 3 is the way to go.

Although the question relates to Ubuntu, let me contribute by saying that I'm on Mac and my python command defaults to Python 2.7.5. I have Python 3 as well, accessible via python3, so knowing the pip package origin, I just downloaded it and issued sudo python3 setup.py install against it and, surely enough, only Python 3 has now this module inside its site packages. Hope this helps a wandering Mac-stranger.

Execute the pip binary directly.
First locate the version of PIP you want.
jon-mint python3.3 # whereis ip
ip: /bin/ip /sbin/ip /usr/share/man/man8/ip.8.gz /usr/share/man/man7/ip.7.gz
Then execute.
jon-mint python3.3 # pip3.3 install pexpect
Downloading/unpacking pexpect
Downloading pexpect-3.2.tar.gz (131kB): 131kB downloaded
Running setup.py (path:/tmp/pip_build_root/pexpect/setup.py) egg_info for package pexpect
Installing collected packages: pexpect
Running setup.py install for pexpect
Successfully installed pexpect
Cleaning up...

You should install ALL dependencies:
sudo apt-get install build-essential python3-dev python3-setuptools python3-numpy python3-scipy libatlas-dev libatlas3gf-base
Install pip3(if you have installed, please look step 3):
sudo apt-get install python3-pip
Iinstall scikit-learn by pip3
pip3 install -U scikit-learn
Open your terminal and entry python3 environment, type import sklearn to check it.

To install pip for python3 use should use pip3 instead of pip.
To install python in ubuntu 18.08 bionic
before installing a version of python, activate virtual environment so that it won't have any problem in a future versions of python.
virtualenv -p /usr/bin/python3 py3env
source py3env/bin/activate
then install the actual python version you want.
>> sudo apt-get install python3.7
To install the required pip package in ubuntu
>> sudo apt-get install python3-pip

You Can Simply type in terminal/console .
Commands
sudo apt update
sudo apt upgrade
sudo apt install python3-pip3
pip3 install package-name

Another way to install python3 is using wget. Below are the steps for installation.
wget http://www.python.org/ftp/python/3.3.5/Python-3.3.5.tar.xz
tar xJf ./Python-3.3.5.tar.xz
cd ./Python-3.3.5
./configure --prefix=/opt/python3.3
make && sudo make install
Also,one can create an alias for the same using
echo 'alias py="/opt/python3.3/bin/python3.3"' >> ~/.bashrc
Now open a new terminal and type py and press Enter.