Q:

Click and drag a rectangle with pygame

I'm new to pygame and I'm writing a program that allows the user to click and drag a rectangle around the pygame window, then sends it's coordinates through a socket. I can move the rectangle on mouse click, but I've been messing around with it for a while and still can't figure out how to implement click and drag. Any help would be appreciated. Here's the relevant code:
from pygame.locals import *
import socket, pygame, time 
#define variables
x = y = 0
screen = pygame.display.set_mode((430, 410))
targetRectangle = pygame.draw.rect(screen, (255, 0, 0), (176, 134, 7, 7))
pygame.display.flip()
#define smaller functions
  #define function to start pygame window  
def startPygame():
  pygame.display.set_caption(option + " Tracking System")
  pygame.mouse.set_visible(True)
  screen.fill((255, 255, 255))
  targetRectangle = pygame.draw.rect(screen, (255, 0, 0), (176, 134, 7, 7))
  pygame.display.flip()
  #define function to update pygame window 
def updateWindow():
  screen.fill((255, 255, 255))
  global targetRectangle
  global xPosition
  global yPosition
  targetRectangle = pygame.draw.rect(screen, (255, 0, 0), (xPosition, yPosition, 7, 7))
  pygame.display.flip()
#define main functions
def collectMouseData():
  startPygame()
  print "\n"
  print "mouse tracking system"
    #wait until a mouse button is clicked
  running = 1
  while running == 1:
    event = pygame.event.poll()
    if event.type == pygame.QUIT:
      c.send("quit")
      pygame.quit()
      running = 0
    #see if a mousebutton is down
    elif event.type == pygame.MOUSEBUTTONDOWN:
      xMouse = event.pos[0]
      yMouse = event.pos[1]
      #see if mouse click collides with targetRectangle 
      if targetRectangle.collidepoint(xMouse, yMouse):
        global xPosition
        xPosition = event.pos[0]
        global yPosition
        yPosition = event.pos[1]
        updateWindow()
        global targetRectangle
        sendData(targetRectangle)

A:

You have to use 

MOUSEBUTTONDOWN to check if object was clicked and set drag = True (and remember offset between mouse position and rectangle top-left corner)
MOUSEBUTTONUP to set drag = False
MOUSEMOTION to move object when drag == True using mouse position and offset.

Working example
import pygame

# --- constants --- (UPPER_CASE names)

SCREEN_WIDTH = 430
SCREEN_HEIGHT = 410

#BLACK = (  0,   0,   0)
WHITE = (255, 255, 255)
RED   = (255,   0,   0)

FPS = 30

# --- classses --- (CamelCase names)

# empty

# --- functions --- (lower_case names)

# empty

# --- main ---

# - init -

pygame.init()

screen = pygame.display.set_mode((SCREEN_WIDTH, SCREEN_HEIGHT))
#screen_rect = screen.get_rect()

pygame.display.set_caption("Tracking System")

# - objects -

rectangle = pygame.rect.Rect(176, 134, 17, 17)
rectangle_draging = False

# - mainloop -

clock = pygame.time.Clock()

running = True

while running:

    # - events -

    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False

        elif event.type == pygame.MOUSEBUTTONDOWN:
            if event.button == 1:            
                if rectangle.collidepoint(event.pos):
                    rectangle_draging = True
                    mouse_x, mouse_y = event.pos
                    offset_x = rectangle.x - mouse_x
                    offset_y = rectangle.y - mouse_y

        elif event.type == pygame.MOUSEBUTTONUP:
            if event.button == 1:            
                rectangle_draging = False

        elif event.type == pygame.MOUSEMOTION:
            if rectangle_draging:
                mouse_x, mouse_y = event.pos
                rectangle.x = mouse_x + offset_x
                rectangle.y = mouse_y + offset_y

    # - updates (without draws) -

    # empty

    # - draws (without updates) -

    screen.fill(WHITE)

    pygame.draw.rect(screen, RED, rectangle)

    pygame.display.flip()

    # - constant game speed / FPS -

    clock.tick(FPS)

# - end -

pygame.quit()

EDIT: other examples with many rectangles or circles and buttons on GitHub: 
furas/python-examples/pygame/drag-rectangles-circles

