pyserial

You can set timeout = None, then the read call will block until the requested number of bytes are there. If you want to wait until data arrives, just do a read(1) with timeout None. If you want to check data without blocking, do a read(1) with timeout zero, and check if it returns any data

#Modified code from main loop: 
s = serial.Serial(5)

#Modified code from thread reading the serial port
while 1:
  tdata = s.read()           # Wait forever for anything
  time.sleep(1)              # Sleep (or inWaiting() doesn't give the correct value)
  data_left = s.inWaiting()  # Get the number of characters ready to be read
  tdata += s.read(data_left) # Do the read and combine it with the first character

  ... #Rest of the code

you should set the baud rate in your serial.Serial(...) command, otherwise the camera might not recognize whatever command you're sending there. something along the lines of:

cam = serial.Serial("/dev/ttyUSB0", baudrate=9600)

Also, you may specify the timeout as a parameter, with the possible values:

timeout = None: wait forever
timeout = 0: non-blocking mode (return immediately on read)
timeout = x: set timeout to x seconds

#!/usr/bin/python

import serial, time
#initialization and open the port

#possible timeout values:
#    1. None: wait forever, block call
#    2. 0: non-blocking mode, return immediately
#    3. x, x is bigger than 0, float allowed, timeout block call

ser = serial.Serial()
#ser.port = "/dev/ttyUSB0"
ser.port = "/dev/COM5"
#ser.port = "/dev/ttyS2"
ser.baudrate = 9600
ser.bytesize = serial.EIGHTBITS #number of bits per bytes
ser.parity = serial.PARITY_NONE #set parity check: no parity
ser.stopbits = serial.STOPBITS_ONE #number of stop bits
#ser.timeout = None          #block read
ser.timeout = 1            #non-block read
#ser.timeout = 2              #timeout block read
ser.xonxoff = False     #disable software flow control
ser.rtscts = False     #disable hardware (RTS/CTS) flow control
ser.dsrdtr = False       #disable hardware (DSR/DTR) flow control
ser.writeTimeout = 2     #timeout for write

try: 
    ser.open()
except Exception, e:
    print "error open serial port: " + str(e)
    exit()

if ser.isOpen():

    try:
        ser.flushInput() #flush input buffer, discarding all its contents
        ser.flushOutput()#flush output buffer, aborting current output 
                 #and discard all that is in buffer

        #write data
        ser.write("AT+CSQ")
        print("write data: AT+CSQ")

       time.sleep(0.5)  #give the serial port sometime to receive the data

       numOfLines = 0

       while True:
          response = ser.readline()
          print("read data: " + response)

        numOfLines = numOfLines + 1

        if (numOfLines >= 5):
            break

        ser.close()
    except Exception, e1:
        print "error communicating...: " + str(e1)

else:
    print "cannot open serial port "

import serial

port = serial.Serial("/dev/ttyAMA0", baudrate=115200, timeout=3.0)

while True:
    port.write("\r\nSay something:")
    rcv = port.read(10)
    port.write("\r\nYou sent:" + repr(rcv))

import serial.tools.list_ports
list = serial.tools.list_ports.comports()
connected = []
for element in list:
    connected.append(element.device)
print("Connected COM ports: " + str(connected))

# deu pau por permissao denied
# sudo adduser MyUser dialout
# sudo chmod a+rw /dev/ttyUSB0


ser = serial.Serial(
    port='/dev/ttyUSB0',\
    baudrate=9600,\
    parity=serial.PARITY_NONE,\
    stopbits=serial.STOPBITS_ONE,\
    bytesize=serial.EIGHTBITS,\
    timeout=0, \
    xonxoff=False, \
    dsrdtr=False, \
    rtscts=False)

print "esta aberto:", ser.is_open
ser.write("\r\nDiga algo:")
rcv = ser.readline()
ser.write("\r\nVoce mandou:" + repr(rcv))