import sys
sys.exit()

List all available video devices

# Example 1
import cv2
def testDevice(source):
   cap = cv2.VideoCapture(source) 
   if cap is None or not cap.isOpened():
       print('Warning: unable to open video source: ', source)

testDevice(0) # no printout
testDevice(1) # prints message

# Example 2
def listAllAvailableVideoDevice():
    index = 0
    arr = []
    while True:
        cap = cv2.VideoCapture(index)
        if not cap.read()[0]:
            break
        else:
            arr.append(index)
        cap.release()
        index += 1
    return arr

How to generate a executable file

1. python -m pip install pyinstaller
2. pyinstaller -F .hello.py -i search.ico -c --onedir --onefile --clean --noupx
3. It will generate an executable file in dist folder. If the executable file needs some config files for executing. You have to copy them to the dist folder.
4. If I add -w option, pyinstaller generates an error message Error loading Python DLL: C:UsersAfroAppDataLocalTemp_MEI51322python35.dll(error code 193). I don’t know why.
5. Reference error-when-creating-executable-file-with-pyinstaller

locate python executable file

import sys
print(sys.executable)

if then else statement on one line

'Yes' if fruit == 'Apple' else 'No'

test none type

if variable is None:

create a multiline string variable

s = """
I will %s there
I will go %s
%s
""" % (string1, string2, string3)

extract the substring between two markers

import re
print re.search('AAA(.*?)ZZZ', 'gfgfdAAA1234ZZZuijjk').group(1)

Reference

• RegexOne - Learn Regular Expressions - Python
• Pythex: a Python regular expression editor