Install py2 first! Install py3 later.
Download and install py3 from the official website.
During installation, make sure to "add to system PATH".
If it is only in user's "Path", we need to also add to system "PATH" (both the python root folder and the script subfolder), and make sure it is before py2's folders.
Ubuntu 16.04 has both py2 & py3; default py2.
INSTALL PIP IN UBUNTU 16
sudo apt-get update && sudo apt-get -y upgrade && \ sudo apt-get install python-pip python3-pip && \ pip -V; pip3 -V
FREQUENT PIP CMD
pip install package_name pip uninstall package_name pip search package_name pip freeze pip --help
There are 2 tools (
virtualenvwrapper) can be used. There is also one blog introducing bash alias way to use
virtualenv: ref ( evernote backup ).
We will use the wrapper one (cuz we prefer new stuff, right?).
If we need to put the env into a folder other than the user's home, we can use the old
virtualenv [-p /usr/bin/python2.6] <path/to/new/virtualenv/>
pip install virtualenvwrapper-win
pip install virtualenvwrapper (this also works for windows with cygwin)
make new env
mkvirtualenv <env name>
If we want to use another python intepretor, we can use the optional
-p (path) parameter:
mkvirtualenv -p D:\Python27\python.exe py27_rest_demo
TIP: After running this command, we will automatically enter the virtual environment.
The name is showing at the beginning of terminal/cmd prompt, surrended by
OBS: newly created env does NOT have globally installed packages.
using previously created env
workon <env name>
When we are in an env, we can use
pip to install packages for this env.
quit current env
test package version
Take Django as an example:
import django print(django.get_version())
-p parameter, we need to run the .py files with virtual env's python.exe, e.g.:
C:\Users\<user name>\Envs\py27_rest_demo\Scripts\python.exe manage.py runserver
Otherwise, system's global intepretor will take effect.
We can use
D:\Python27>mklink python27.exe python.exe to make it possible to run server by:
python27.exe manage.py runserver. However, direct copying python.exe and renaming the file does NOT work.
import time start_time = time.time() # do something here end_time = time.time() print(end_time - start_time, 'seconds.')