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Friday, September 22, 2017

The python-vlc python module.

The python module for vlc is named python-vlc.
This python module let you test libvlc API like the VLC video player.
You can install it easily with pip python tool.
C:\Python27\Scripts>pip2.7.exe install python-vlc
Collecting python-vlc
  Downloading python-vlc-1.1.2.tar.gz (201kB)
    100% |################################| 204kB 628kB/s
Installing collected packages: python-vlc
  Running setup.py install for python-vlc ... done
Successfully installed python-vlc-1.1.2
Let's see a simple example with this python module:
import os
import sys
import vlc
import pygame
 
def call_vlc(self, player):
 
    player.get_fps()
    player.get_time()
 
if len( sys.argv )< 2 or len( sys.argv )> 3:
        print 'Help: python vlc_001.py your_video.mp4'
else:
    pygame.init()
    screen = pygame.display.set_mode((800,600),pygame.RESIZABLE)
    pygame.display.get_wm_info()
    pygame.display.get_driver()

 
    # get path to movie specified as command line argument
    movie = os.path.expanduser(sys.argv[1])
    # see if movie is accessible
    if not os.access(movie, os.R_OK):
        print('Error: %s wrong read file: ' % movie)
        sys.exit(1)
 
    # make instane of VLC and create reference to movie.
    vlcInstance = vlc.Instance()
    media = vlcInstance.media_new(movie)
 
    # make new instance of vlc player
    player = vlcInstance.media_player_new()
 
    # start with a callback
    em = player.event_manager()
    em.event_attach(vlc.EventType.MediaPlayerTimeChanged, \
        call_vlc, player)
 
    # set pygame window id to vlc player
    win_id = pygame.display.get_wm_info()['window']
    if sys.platform == "win32": # for Windows
        player.set_hwnd(win_id)
 
    # load movie into vlc player instance
    player.set_media(media)
 
    # quit pygame mixer to allow vlc full access to audio device
    pygame.mixer.quit()
 
    # start movie play
    player.play()
 
    while player.get_state() != vlc.State.Ended:
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                sys.exit(2)
The base of this python script is to make an instance of vlc and put into the pygame display.
Another simple example:
C:\Python27>python.exe
Python 2.7.13 (v2.7.13:a06454b1afa1, Dec 17 2016, 20:42:59) [MSC v.1500 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import vlc
>>> inst = vlc.Instance()
Warning: option --plugin-path no longer exists.
Warning: option --plugin-path no longer exists.
>>> med = inst.media_new('rain.mp4')
>>> p = med.player_new_from_media()
>>> p.play()
0
>>>

Tuesday, September 19, 2017

The numba python module - part 002 .

Today I tested how fast is jit from numba python and fibonacci math function.
You will see strange output I got for some values.
First example:
import numba
from numba import jit
from timeit import default_timer as timer

def fibonacci(n):
    a, b = 1, 1
    for i in range(n):
        a, b = a+b, a
    return a
fibonacci_jit = jit(fibonacci)

start = timer()
fibonacci(100)
duration = timer() - start

startnext = timer()
fibonacci_jit(100)
durationnext = timer() - startnext

print(duration, durationnext)
The result of this run is:
C:\Python27>python numba_test_003.py
(0.00018731270733896962, 0.167499256682878)

C:\Python27>python numba_test_003.py
(1.6357787798437412e-05, 0.1683614083221368)

C:\Python27>python numba_test_003.py
(2.245186560569841e-05, 0.1758382003097716)

C:\Python27>python numba_test_003.py
(2.3093347480146938e-05, 0.16714964906130353)

C:\Python27>python numba_test_003.py
(1.5395564986764625e-05, 0.17471143739730277)

C:\Python27>python numba_test_003.py
(1.5074824049540363e-05, 0.1847134227837042)
As you can see the fibonacci function is not very fast.
The jit - just-in-time compile is very fast.
Let's see if the python source code may slow down.
Let's see the new source code with jit will not work well:
import numba
from numba import jit
from timeit import default_timer as timer

def fibonacci(n):
    a, b = 1, 1
    for i in range(n):
        a, b = a+b, a
    return a
fibonacci_jit = jit(fibonacci)

start = timer()
print fibonacci(100)
duration = timer() - start

startnext = timer()
print fibonacci_jit(100)
durationnext = timer() - startnext

print(duration, durationnext)
The result is this:
C:\Python27>python numba_test_003.py
927372692193078999176
1445263496
(0.0002334994022992635, 0.17628787910376)

C:\Python27>python numba_test_003.py
927372692193078999176
1445263496
(0.0006886307922204926, 0.17579169287387408)

C:\Python27>python numba_test_003.py
927372692193078999176
1445263496
(0.0008105123483657127, 0.18209553525407973)

C:\Python27>python numba_test_003.py
927372692193078999176
1445263496
(0.00025466830415606486, 0.17186550306131188)

C:\Python27>python numba_test_003.py
927372692193078999176
1445263496
(0.0007348174871807866, 0.17523103771560608)
The result for value 100 is not the same: 927372692193078999176 and 1445263496.
The first problem is:
The problem is that numba can't intuit the type of lookup. If you put a print nb.typeof(lookup) in your method, you'll see that numba is treating it as an object, which is slow.
The second problem is the output but can be from the same reason.
I test with value 5 and the result is :
C:\Python27>python numba_test_003.py
13
13
13
13
(0.0007258367409385072, 0.17057997338491704)

C:\Python27>python numba_test_003.py
13
13
(0.00033709872502270044, 0.17213235952108247)

C:\Python27>python numba_test_003.py
13
13
(0.0004836773333341886, 0.17184433415945508)

C:\Python27>python numba_test_003.py
13
13
(0.0006854233828482501, 0.17381272129120037)