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using an older version of scikit-learn

I have conda 4.5.11 installed in my machine and Python 3.7.0 and I am trying to install scikit-learn 0.19 using the following procedure:
pip uninstall scikit-learn
pip install scikit-learn==0.19
but I get the following errors:
Failed building wheel for scikit-learn
Command "/anaconda3/bin/python -u -c "import setuptools, tokenize;file='/private/var/folders/x5/t6zy26vd4gq36xgq6yl45p2h0000gn/T/pip-install-7h06grkn/scikit-learn/setup.py';f=getattr(tokenize, 'open', open)(file);code=f.read().replace('\r\n', '\n');f.close();exec(compile(code, file, 'exec'))" install --record /private/var/folders/x5/t6zy26vd4gq36xgq6yl45p2h0000gn/T/pip-record-eem8zdll/install-record.txt --single-version-externally-managed --compile" failed with error code 1 in /private/var/folders/x5/t6zy26vd4gq36xgq6yl45p2h0000gn/T/pip-install-7h06grkn/scikit-learn/
and a bunch of warnings too. How can I use an older version of sklearn with an anaconda installation of python?

conda install scikit-learn==0.19 worked.

I had a similar issue, needed scikit-learn==0.18.1. What worked for me was uninstalling the current Conda, going to https://repo.anaconda.com/archive/ and finding the version that I needed.
For reference, the one that worked for me was: Anaconda3-4.3.1-Windows-x86_64.exe from March 2017.
After that, restart the IDE, and all dependencies were on the version I needed.

"Microsoft Visual C++ … is required" error when trying to install pyodbc on Windows

I am trying to install pyodbc, and I am getting the below error.
C:\Python\Python37\Scripts>pip3 install pyodbc
Output
Collecting pyodbc
Using cached https://files.pythonhosted.org/packages/aa/71/cef225c4889620a1a00251d24c1746fe0cf4124290a75d1c2dc5c187b61f/pyodbc-4.0.23.tar.gz
Installing collected packages: pyodbc
Running setup.py install for pyodbc ... error
Complete output from command c:\python\python37\python.exe -u -c "import setuptools, tokenize;__file__='C:\\Users\\Alankar\\AppData\\Local\\Temp\\pip-install-7qf14pkz\\pyodbc\\setup.py';f=getattr(tokenize, 'open', open)(__file__);code=f.read().replace('\r\n', '\n');f.close();exec(compile(code, __file__, 'exec'))" install --record C:\Users\Alankar\AppData\Local\Temp\pip-record-k11gmg0x\install-record.txt --single-version-externally-managed --compile:
running install
running build
running build_ext
building 'pyodbc' extension
error: Microsoft Visual C++ 14.0 is required. Get it with "Microsoft Visual C++ Build Tools": http://landinghub.visualstudio.com/visual-cpp-build-tools
Command "c:\python\python37\python.exe -u -c "import setuptools, tokenize;__file__='C:\\Users\\Alankar\\AppData\\Local\\Temp\\pip-install-7qf14pkz\\pyodbc\\setup.py';f=getattr(tokenize, 'open', open)(__file__);code=f.read().replace('\r\n', '\n');f.close();exec(compile(code, __file__, 'exec'))" install --record C:\Users\Alankar\AppData\Local\Temp\pip-record-k11gmg0x\install-record.txt --single-version-externally-managed --compile" failed with error code 1 in C:\Users\Alankar\AppData\Local\Temp\pip-install-7qf14pkz\pyodbc\

I couldn't get the C++ build tools method to work, but I found this method to be very straightforward:
Download the relevant pyodbc wheel (pre-compiled binary) based on your computer's architecture and version of Python: https://www.lfd.uci.edu/~gohlke/pythonlibs/#pyodbc
Run pip install <wheel path>.
For example:
pip install c:\users\bob\downloads\pyodbc-4.0.27-cp38-cp38-win_amd64.whl

Some Libraries require C++ build tools to install. In your case, to solve this problem there are two methods which are:
Update the pip's Setup tool:
To fix your error update the setup tool by this command:
pip install --upgrade setuptools
And the second method is to:
Install the Microsoft Visual C++ Build Tools
This can also be fixed by installing this little tool provided by Microsoft:
https://visualstudio.microsoft.com/visual-cpp-build-tools/

the install failed on my machine even after I installed Microsoft VC++ build tools, my solution for this is install an early version. the newer version assume you have VC++ and VS 2019 installed.
run this command
pip install -Iv pyodbc==4.0.27

If none of the other answers work:
I was running the newest version of python and it was giving me this error.
As soon as I downgraded to 3.8.x it worked like a charm using pip install

Error while installing mysqlclient for python in Windows 10

I use this command for installing MySQL client:
pip install mysqlclient
And then I see this problem:
running build_ext
building '_mysql' extension
error: Microsoft Visual C++ 10.0 is required. Get it with "Microsoft Windows SDK 7.1": www.microsoft.com/download/details.aspx?id=8279
Cleaning up... Command C:\Python34\python.exe -c "import setuptools,
tokenize;file='C:\Users\Jayed\AppData\Local\Temp\pip_build_Jayed\mysqlclient\setup.py';exec(compile(getattr(tokenize,
'open', open)(file).read().replace('\r\n', '\n'), file,
'exec'))" install --record
C:\Users\Jayed\AppData\Local\Temp\pip-l4c6dhkk-record\install-record.txt
--single-version-externally-managed --compile failed with error code 1 in C:\Users\Jayed\AppData\Local\Temp\pip_build_Jayed\mysqlclient
Storing debug log for failure in C:\Users\Jayed\pip\pip.log

Actually I went down this path. While I suppose you can find all the libraries and components you need to get the client to compile, it is telling you it can't find a compiled copy of the client and is trying to compile it to install it.
Follow the instructions here: https://pypi.org/project/mysqlclient/ (it has notes about windows doing what you are describing) or download the wheel file (from downloads link on the page) and type
pip install mysqlclient.whl
and it will install without demanding C++ in order to use mysql with python.

Installing Scipy for Windows

I am trying to install Scipy on my computer. I did it by using the command pip install Scipy. (pip & numpy are up-to-date and I am using Python 3.6) I also tried it with Pycharm, but it didn't worked either.
I always do get this Error:
Command
"c:\users***\appdata\local\programs\python\python36\python.exe -u -c
"import setuptools,
tokenize;file='C:\Users\***\AppData\Local\Temp\pip-build-x3s21920\scipy\setup.py';f=getattr(tokenize,
'open', open)(file);code=f.read().replace('\r\n',
'\n');f.close();exec(compile(code, file, 'exec'))" install
--record C:\Users***\AppData\Local\Temp\pip-gr9ppj_q-record\install-record.txt
--single-version-externally-managed --compile" failed with error code 1 in C:\Users***\AppData\Local\Temp\pip-build-x3s21920\scipy\
Does anyone has an idea of what I can do?

Try to install it from the following binaries
http://www.lfd.uci.edu/~gohlke/pythonlibs/
These are unofficial precompiled binaries

can't install mysql-connector on Python 3.5.3 with pip3

I have successfully installed mysql-connector using 'pip install mysql-connector', however it installs to the Mac OSX standard version of Python (2.7).
I need it installed to my latest version of Python (3.5.3).
When I use 'pip3 install mysql-connector' or 'pip3 install --allow-external mysql-connector mysql-connector' I get the following errors:
Error 1:
Failed building wheel for mysql-connector
Error 2:
Command "/Library/Frameworks/Python.framework/Versions/3.5/bin/python3.5 -u -c "import setuptools, tokenize;__file__='/private/var/folders/ch/vzgxn0n119zggbgnb0_vg5400000gn/T/pip-build-po0zonwm/mysql-connector/setup.py';f=getattr(tokenize, 'open', open)(__file__);code=f.read().replace('\r\n', '\n');f.close();exec(compile(code, __file__, 'exec'))" install --record /var/folders/ch/vzgxn0n119zggbgnb0_vg5400000gn/T/pip-q6b3vmy3-record/install-record.txt --single-version-externally-managed --compile" failed with error code 1 in /private/var/folders/ch/vzgxn0n119zggbgnb0_vg5400000gn/T/pip-build-po0zonwm/mysql-connector/
Does anyone know how to resolve this problem? I don't want to have to switch back to Python 2.7.
Thanks.

This will do the thing:
pip3 install mysql-connector-python