Python, OpenCV: Video Capture and Display

OpenCV: Video Capture

import time
import cv2

video_capture = cv2.VideoCapture(0)
while True:
    t0=time.time()
    ret, frame = video_capture.read()
    t1=time.time()
    print "passed ", t1-t0, "s"

    cv2.imshow('Video', frame)
    #on pressing "q" exit
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break
        
video_capture.release()
cv2.destroyAllWindows()  

Frames Per Second Counter

#test how many frames per second for a webcam
import time
import cv2

video_capture = cv2.VideoCapture(1)
t0 = time.time()
i=0
while True:
    ret, frame = video_capture.read()
    print frame.shape
    t = time.time()
    if t-t0 > 1:
        t0=t
        print "frames ",i
        i=0
        
    i+=1    
                    
    cv2.imshow('Video', frame)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break
        
video_capture.release()
cv2.destroyAllWindows()   

Python: JSON socket - Server/Client Structure

JSON Socket Library

#file:jsonsocket.py
#https://github.com/mdebbar/jsonsocket
import json, socket

class Server(object):
  """
  A JSON socket server used to communicate with a JSON socket client. All the
  data is serialized in JSON. How to use it:

  server = Server(host, port)
  while True:
    server.accept()
    data = server.recv()
    # shortcut: data = server.accept().recv()
    server.send({'status': 'ok'})
  """

  backlog = 5
  client = None

  def __init__(self, host, port):
    self.socket = socket.socket()
    self.socket.bind((host, port))
    self.socket.listen(self.backlog)

  def __del__(self):
    self.close()

  def accept(self):
    # if a client is already connected, disconnect it
    if self.client:
      self.client.close()
    self.client, self.client_addr = self.socket.accept()
    return self

  def send(self, data):
    if not self.client:
      raise Exception('Cannot send data, no client is connected')
    _send(self.client, data)
    return self

  def recv(self):
    if not self.client:
      raise Exception('Cannot receive data, no client is connected')
    return _recv(self.client)

  def close(self):
    if self.client:
      self.client.close()
      self.client = None
    if self.socket:
      self.socket.close()
      self.socket = None


class Client(object):
  """
  A JSON socket client used to communicate with a JSON socket server. All the
  data is serialized in JSON. How to use it:

  data = {
    'name': 'Patrick Jane',
    'age': 45,
    'children': ['Susie', 'Mike', 'Philip']
  }
  client = Client()
  client.connect(host, port)
  client.send(data)
  response = client.recv()
  # or in one line:
  response = Client().connect(host, port).send(data).recv()
  """

  socket = None

  def __del__(self):
    self.close()

  def connect(self, host, port):
    self.socket = socket.socket()
    self.socket.connect((host, port))
    return self

  def send(self, data):
    if not self.socket:
      raise Exception('You have to connect first before sending data')
    _send(self.socket, data)
    return self

  def recv(self):
    if not self.socket:
      raise Exception('You have to connect first before receiving data')
    return _recv(self.socket)

  def recv_and_close(self):
    data = self.recv()
    self.close()
    return data

  def close(self):
    if self.socket:
      self.socket.close()
      self.socket = None

## helper functions ##

def _send(socket, data):
  try:
    serialized = json.dumps(data)
  except (TypeError, ValueError), e:
    raise Exception('You can only send JSON-serializable data')
  # send the length of the serialized data first
  socket.send('%d\n' % len(serialized))
  # send the serialized data
  socket.sendall(serialized)

def _recv(socket):
  # read the length of the data, letter by letter until we reach EOL
  length_str = ''
  char = socket.recv(1)
  while char != '\n':
    length_str += char
    char = socket.recv(1)
  total = int(length_str)
  # use a memoryview to receive the data chunk by chunk efficiently
  view = memoryview(bytearray(total))
  next_offset = 0
  while total - next_offset > 0:
    recv_size = socket.recv_into(view[next_offset:], total - next_offset)
    next_offset += recv_size
  try:
    deserialized = json.loads(view.tobytes())
  except (TypeError, ValueError), e:
    raise Exception('Data received was not in JSON format')
  return deserialized

Server

#file:server.py
from jsonsocket import Server

host = 'LOCALHOST'
port = 8080

server = Server(host, port)

while True:
    server.accept()
    data = server.recv()
    server.send({"response":data})

server.close()

Client

#file:client.py
from jsonsocket import Client
import time

host = 'LOCALHOST'
port = 8080

i=1
while True:
    client = Client()
    client.connect(host, port).send({'test':i})
    i+=1
    response = client.recv()
    print response
    client.close()
    time.sleep(1)

Python: Pitfalls Filled

# list to string, separated by comma
lis = [1,2,3]
print ",".join(map(str, lis))

# print system time in formated way - logging time
from time import gmtime, strftime
strftime("%Y-%m-%d %H:%M:%S", gmtime())

#appending dict or merging two dicts
b={}
d=b.copy()
d.update({'list':0})

#joining dict with string
yook = {'a':0,'img':['url2','url2']}
print str(yook) + "asd"

#pretty print (json - dict)
a= {u'response': {u'url': u'http://www.faceplusplus.com/static/img/demo/9.jpg', u'img_id': u'2081892e329727f350337509ff939a29', u'img_width': 540, u'session_id': u'd6fdce4b591e43dabbd8d31f68db0a46', u'face': [{u'attribute': {u'gender': {u'confidence': 99.7639, u'value': u'Male'}, u'age': {u'range': 9, u'value': 23}, u'race': {u'confidence': 99.9662, u'value': u'White'}, u'smiling': {u'value': 13.909}}, u'face_id': u'42dd2bdec1f8fae250a8d4c6b5f11837', u'tag': u'', u'position': {u'eye_left': {u'y': 44.727248, u'x': 58.625}, u'center': {u'y': 46.730245, u'x':59.537037}, u'width': 5.0, u'mouth_left': {u'y': 47.659401, u'x': 58.412037}, u'height': 7.356948, u'mouth_right': {u'y': 47.838692, u'x': 60.201481}, u'nose':{u'y': 46.782834, u'x': 59.463519}, u'eye_right': {u'y': 44.922616, u'x': 60.493333}}}], u'img_height': 367}}

from pprint import pprint
pprint(a)

It is prettier, isn't it?

{u'response': {u'face': [{u'attribute': {u'age': {u'range': 9,
                                                  u'value': 23},
                                         u'gender': {u'confidence': 99.7639,
                                                     u'value': u'Male'},
                                         u'race': {u'confidence': 99.9662,
                                                   u'value': u'White'},
                                         u'smiling': {u'value': 13.909}},
                          u'face_id': u'42dd2bdec1f8fae250a8d4c6b5f11837',
                          u'position': {u'center': {u'x': 59.537037,
                                                    u'y': 46.730245},
                                        u'eye_left': {u'x': 58.625,
                                                      u'y': 44.727248},
                                        u'eye_right': {u'x': 60.493333,
                                                       u'y': 44.922616},
                                        u'height': 7.356948,
                                        u'mouth_left': {u'x': 58.412037,
                                                        u'y': 47.659401},
                                        u'mouth_right': {u'x': 60.201481,
                                                         u'y': 47.838692},
                                        u'nose': {u'x': 59.463519,
                                                  u'y': 46.782834},
                                        u'width': 5.0},
                          u'tag': u''}],
               u'img_height': 367,
               u'img_id': u'2081892e329727f350337509ff939a29',
               u'img_width': 540,
               u'session_id': u'd6fdce4b591e43dabbd8d31f68db0a46',
               u'url': u'http://www.faceplusplus.com/static/img/demo/9.jpg'}}

Windows DOS Batch: Rename all the folders numerically

The following snippet renames all folders in current directory to numbers starting from 0.

set i=0
for %f in (*) do (set /A "i=i+1")

References

• SS64 NT For Loop

Python: Call Function From String

Somehow there is a need to make calls from string, i.e. I have the name of the functions in string, now I need to call that function from that string.

import inspect

class API:
    def f1(self):
        print "f1 is called from",self.__class__.__name__
        
def f1():
    print "f1 is called from",inspect.stack()[0][3]
        
api = API()
a = "f1"

globals()[a]()
getattr(api,a)()

The results should be

f1 is called from f1
f1 is called from API

Windows cmd: Create Incrementing Folders With For Loop

Bring up Windows console with Win+R and cmd, type

for /l %i in (1,1,100);do mkdir %i

Syntax

      FOR /L %%parameter IN (start,step,end) DO command 

Notice that, double percentage symbol is used for batch file, and on the command line

%%parameter : A replaceable parameter:
                 in a batch file use %%i (on the command line %i)

References

• For Loop - Windows Console