Keep the color prompt in tmux

To keep your prompt (PS1) with color shown in tmux screen, add the following property in .bashrc:

force_color_prompt=yes

Create docker container with the simple flask application

I will try to create a docker container with the simple flask application created some times ago.

---

First, I create a shell script for starting the flask application, namely "boot.sh":

boot.sh

#!/bin/sh
export FLASK_APP=simple.py
flask run --host 0.0.0.0

---

Second, we need to create a requirements.txt file:

requirements.txt

flask==1.1.1

Actually you can run the following to get the requirements.txt:

pip freeze > requirements.txt

---

Third, together with the simple.py file created in the simple flask application, put those 3 files in an "app" directory:

app/

   - boot.sh

   - requirements.txt

   - simple.py

---

Forth, create a Docker file outside the app directory:

Dockerfile

FROM python:3.6-alpine
WORKDIR /home/app
COPY app/ ./
RUN chmod +x ./boot.sh
RUN pip install -r requirements.txt
EXPOSE 5000
ENTRYPOINT ["./boot.sh"]

Build the docker image using the Dockerfile:

     docker build -t simple:latest .

Run the docker container with the docker image we just created:

     docker run -d -p 5000:5000 simple:latest

Check "http://localhost:5000" to check the Flask application.

Simple Flask sample

Just wanna to create a very simple Flask application in a single python source file:

simple.py

from flask import Flask

application = Flask("simple")

@application.route("/")

def index():

return "Hello World"

To run this Flask application, run the following:

• export FLASK_APP=simple.py
• flask run

If you want to put this application in a Docker container, you need to bind to 0.0.0.0:

• flask run --host 0.0.0.0

Now, navigate "http://localhost:5000" to see the word "Hello World" displayed on the browser.

Navigate tmux splitted pane using mouse

To enable navigation on tmux splitted pane using mouse

In tmux environment, do the following:

1. Ctrl-b
2. Type :setw -g mouse on

Done, try to switch your tmux pane with mouse.

Note:
To make this setting persistent, save this line in .tmux.conf:
setw -g mouse on

Assign locale for moment.js

To assign locale in moment.js, we can use the following:

     moment.locale("en")

It will returns "en". However, if you assign an unaccepted locale to it, it won't update its value. For example:

     moment.locale("zh")

It still returns "en", since "zh" is not an accepted locale for moment.js.

Up till now, moment.js accepts:

     zh-hk
     zh-tw
     zh-cn

Reference: momentjs

QGIS freezes while editing features

There are many possibilities for QGIS to hang / freezes while editing features. But for my experience, I found it often hangs when using a Shapefile layer.

To minimize this kind of problem, I tried to use other feature format (e.g. SpatialLite). And the problem is relieved to some extent.

Have a try and let me know if it helps or not.

Windows equivalent of "wc -l" command in Linux

To count the number lines of files / stdout in Linux, we uses "wc -l" to achieve. In Windows, we use the following instead:

• find /c /v ""

For example, suppose we have a file "sample_file.txt" and we want to know the number of lines of that file, we can perform the following:

• type sample_file.txt | find /c /v ""

Handling table names with underscore ("_") in flask_sqlalchemy / Python

When you create table class using flask_sqlalchemy (the Flask extension for SQLAlchemy), it can maps the modal class to a proper table automatically. This is cool but if you have a table name with underscore (e.g. MY_SAMPLE_TABLE) and you name your model class with the underscore ('_') as usual, you will find SQLAlchemy will map your table name as something the following:

"MY__SAMPLE__TABLE"

Each single underscore (_) with becomes a double underscores (__). This is annoying and you might believe this is a bug, but in fact you can resolve this issues by naming your table class using the PEP8 naming convention, and named your class as:

class MySampleTable(db.Model):
     field_id = db.Column(db.Integer, primary_key = True)
     field_data = db.Column(db.String(200))

The the SQLAlchemy will map the MySampleTable class to table name as "MY_SAMPLE_TABLE" correctly.

For more information about PEP8, click here for details.

A job with mixture of joy and technology

Job with LEGO + IT, what else I can asked for ?

Connecting Oracle with Python via cx_Oracle extension

Installation Prerequisites

• Python 2.7, 3.5 or above
• Oracle Client / Oracle Instant Client "Basic" or "Basic Light"
• libaio / libaio1 package

Installation Reference

• cx_Oracle
• Installation guide

Sample Python Code

import cx_Oracle

# Make DSN address. Real values for host address, port and service name were replaced by '<>'.
dsn = cx_Oracle.makedsn('<host_address>', '<port>', service_name='<service_name>')

# Connect to DSN
orcl = cx_Oracle.connect(user='<username>', password='<password>', dsn=dsn)

# Get cursor
cursor = orcl.cursor()

# Execute SQL statement
cursor.execute('<SQL SELECT STATEMENT>')

# Fetch result
data = cursor.fetchone()