Python 2 is needed by Deepin and mustn't be replaced.
You can have both Python 2 and 3 at the same time.
Install Python 3.6 additionally with the following command:
sudo apt-get install python3

deepin pre-install python3 and python2
you can enter python3 in terminal to use python3

/usr/bin/python is a symbolic link to python2.7
if you want to replace the command "python" to python3
enter the command below
sudo ln -sf /usr/bin/python3.5 /usr/bin/python

Thank you!

I recommend pyenv, use pyenv to deploy python in different version.

System already installed.Just run pyton3.

system had installed python3.5 and you can use by “python3”

Web development? I recommend Node.js XD. Python3.x and Python2.x (which is an important part of the system) can be installed in your system at the same time. You don't need to and CAN NOT update the already installed Python2.x to Python3.x, but you can use "apt search python3" to search for any Python3.x packages available for  your system and use "sudo apt install python3x", for example, "sudo apt install python36", to install a certain version of Python3 package.

My concern is that Deepin repositories tend to be behind a little, the OP asked about Python 3.6, Deepin comes with 3.5, but this isn't 3.6. Also the suggestion of installing "apt install python36" is inaccurate, it's "apt install python3.6". But this lack of update seems to be an on-going trend in Deepin which is concerning to me, in example, Google Chrome on the repository has version 63, when 64.0.3282 has been available for a month now having been released on 2018-01-24. Visual Studio Code is also on the repository but was on version 1.8, they are now on version 1.20, while the Google Chrome instance wasn't that huge of a leap in version variance Visual Studio Code is. I've found that in both instances I was able to install via the default deb files and everything worked properly and nothing broke.  How often is the repo updated to keep an accurate and up-to-date account of the software binaries within it?  

my favourite is the source code.
sudo ./configure
sudo make
sudo install
then change the default version

Yea, sometimes you have to compile programs or download unofficial pre-build binary releases from somewhere and it would cause some stability or other compatibility problems, which is really time-consuming and annoying. Compiling GCC 7.2.0 took me hours. I could do nothing but stare at the screen : (, it took up most of the resource from my computer. Compiling Python manually is quite easy though.

开始看到一个英文提问还很担心没人理呢，进来一看，多虑了，论坛大神还是多啊 · · ·  嗯，激励我好好学英文

sudo apt install python3.6