Install virtualenv

# Step 1: Update your repositories

sudo apt-get update

# Step 2: Install pip for Python 3

sudo apt-get install build-essential libssl-dev libffi-dev python-dev

sudo apt install python3-pip

# Step 3: Use pip to install virtualenv

sudo pip3 install virtualenv

# Step 4: Launch your Python 3 virtual environment, here the name of my virtual environment will be env3

virtualenv -p python3 env3

# Step 5: Activate your new Python 3 environment. There are two ways to do this

. env3/bin/activate # or source env3/bin/activate which does exactly the same thing

# you can make sure you are now working with Python 3

python -- version

# this command will show you what is going on: the python executable you are using is now located inside your virtualenv repository

which python

# Step 6: code your stuff

# Step 7: done? leave the virtual environment

deactivate

 

Windows install pip

1. Open cmd as administrator
2. Install python
3. curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py

4. Then run the following command in the folder where you have downloaded get-pip.py:

python get-pip.py

5. Add pip installation path to environment PATH
6. check
pip help

Python locale error: unsupported locale setting

When using pip install, the local error problem occur.

export LC_ALL="en_US.UTF-8"
export LC_CTYPE="en_US.UTF-8"
sudo dpkg-reconfigure locales

Then select en_US.UTF-8 to install

Occurred when install virtualenv.

Install python packages (opencv) in virtual envirenment

source ${env}/bin/activate

pip install opencv-python

if cannot be installed via pip
copy the globally installed package, e.g., OpenCV

cp -R /usr/local/lib/python2.7/dist-packages/xxx ${env}/lib/python2.7/site-packages/

Python-vtk module missing in virtual enviroment

installing Mayavi with pip – no module named vtk

From https://inspro9.wordpress.com/2017/04/03/installing-mayavi-with-pip-no-module-named-vtk/

I had the same problem when installing mayavi with python installed in pyenv, and I solved this problem by copy directory to /home/myname/.pyenv/versions/2.7.12/lib/python2.7/site-packages, below is my method:

1. install vtk and python-vtk

sudo apt-get install vtk6
sudo apt-get install python-vtk

2. try

python -c "import vtk"

if failed again, go to step 3
3. the import error may caused by the loss of vtk package folder in your current python, so we should find the vtk folder and copy to your current python(most possible the python in pyenv shims directory)’s directory .

the path of the vtk folder in my ubuntu is

/usr/lib/python2.7/dist-packages/vtk
just copy the vtk folder to your current python’s /site-packages, e.g.

cp -r /usr/lib/python2.7/dist-packages/vtk /home/myname/pyenv/versions/2.7.12/lib/python2.7/site-packages

4. try this again

python -c "import vtk"

5. if no import error, just do

python2 -m pip install mayavi

Python Time Conversion

From http://emilics.com/blog/article/python_time.html

Python Time Conversion

In python, there are four types that are commonly used to manage time. Timestamps, time tuples, datetime objects, and strings. Programmers often have to convert between these types depending on the situation or API. This article will describe all conversion patterns.

Python Time Conversion Table

Table 1 shows the python conversion table. Click on the pattern you want to see.

Table 1. python time conversion table

input \ output	datetime	time tuple	time stamp	string
datetime	—	datetime ↓ time tuple	datetime ↓ time stamp	datetime ↓ string
time tuple	time tuple ↓ datetime	—	time tuple ↓ time stamp	time tuple ↓ string
time stamp	time stamp ↓ datetime	time stamp ↓ time tuple	—	time stamp ↓ string
string	string ↓ datetime	string ↓ time tuple	string ↓ time stamp	—

datetime → time tuple

>>> dt = datetime.datetime(2010, 12, 31, 23, 59, 59)
>>> tt = dt.timetuple()
>>> print tt
time.struct_time(tm_year=2010, tm_mon=12, tm_mday=31, tm_hour=23, tm_min=59, tm_sec=59, ...)

datetime → time tuple

datetime → time stamp

>>> dt = datetime.datetime(2010, 12, 31, 23, 59, 59)
>>> ts = time.mktime(dt.timetuple())
>>> print ts
1293868799.0

datetime → time stamp

datetime → string

>>> dt = datetime.datetime(2010, 12, 31, 23, 59, 59)
>>> st = dt.strftime('%Y-%m-%d %H:%M:%S')
>>> print st
2010-12-31 23:59:59

datetime → string

time tuple → datetime

>>> tt = (2010, 12, 31, 23, 59, 59, 4, 365, 0)
>>> dt = datetime.datetime(tt[0], tt[1], tt[2], tt[3], tt[4], tt[5])
>>> print dt
2010-12-31 23:59:59
>>>
>>> dt = datetime.datetime(*tt[0:6])  # same with the code above
>>> print dt
2010-12-31 23:59:59

time tuple → datetime

time tuple → time stamp

>>> tt = (2010, 12, 31, 23, 59, 59, 4, 365, 0)
>>> ts = time.mktime(tt)
>>> print ts
1293868799.0

time tuple → time stamp

time tuple → string

>>> tt = (2010, 12, 31, 23, 59, 59, 4, 365, 0)
>>> st = time.strftime('%Y-%m-%d %H:%M:%S', tt)
>>> print st
2010-12-31 23:59:59

time tuple → string

time stamp → datetime

>>> ts = 1293868799.0
>>> dt = datetime.datetime.fromtimestamp(ts)     # for local time
>>> print dt
2010-12-31 23:59:59
>>>
>>> dt = datetime.datetime.utcfromtimestamp(ts)  # for UTC
>>> print dt
2011-01-01 07:59:59

time stamp → datetime

time stamp → time tuple

>>> ts = 1293868799.0
>>> tt = time.localtime(ts)
>>> print tt
time.struct_time(tm_year=2010, tm_mon=12, tm_mday=31, tm_hour=23, tm_min=59, tm_sec=59, ...)
>>>
>>> tt = time.gmtime(ts)
>>> print tt
time.struct_time(tm_year=2011, tm_mon=1, tm_mday=1, tm_hour=7, tm_min=59, tm_sec=59, ...)

time stamp → time tuple

time stamp → string

>>> ts = 1293868799.0
>>> st = datetime.datetime.fromtimestamp(ts).strftime('%Y-%m-%d %H:%M:%S')
>>> print st
2010-12-31 23:59:59
>>>
>>> st = datetime.datetime.utcfromtimestamp(ts).strftime('%Y-%m-%d %H:%M:%S')
>>> print st
2011-01-01 07:59:59

time stamp → string

string → datetime

>>> s = '2010-12-31 23:59:59'
>>> dt = datetime.datetime.strptime(s, '%Y-%m-%d %H:%M:%S')
>>> print dt
2010-12-31 23:59:59

string → datetime

string → time tuple

>>> st = '2010-12-31 23:59:59'
>>> tt = time.strptime(st, '%Y-%m-%d %H:%M:%S')
>>> print tt
time.struct_time(tm_year=2010, tm_mon=12, tm_mday=31, tm_hour=23, tm_min=59, tm_sec=59, ...)

string → time tuple

string → time stamp

>>> s = '2010-12-31 23:59:59'
>>> ts = time.mktime(time.strptime(s, '%Y-%m-%d %H:%M:%S'))
>>> print ts
1293868799.0

string → time stamp