import csv
reader = csv.reader(open("some.csv", "rb"))
for row in reader:
    print row
reader = csv.reader(open("passwd", "rb"), delimiter=':', quoting=csv.QUOTE_NONE)
for row in reader:
    print row
writer = csv.writer(open("some.csv", "wb"))
writer.writerows(someiterable)
csv.register_dialect('unixpwd', delimiter=':', quoting=csv.QUOTE_NONE)
reader = csv.reader(open("passwd", "rb"), 'unixpwd')
filename = "some.csv"
reader = csv.reader(open(filename, "rb"))
try:
    for row in reader:
        print row
except csv.Error, e:
    sys.exit('file %s, line %d: %s' % (filename, reader.line_num, e))
for row in csv.reader(['one,two,three']):
    print row

class Line:
  def __init__(self,p1,p2):
    self.start = p1
    self.end = p2
  def __sub__(self,p):
    if isinstance(p,Point):
      if p is self.start:
        return self.end
      if p is self.end:
          return self.start
class Point:
  def __init__(self,x,y):
    self.x = x
    self.x = x
  def __add__(self,p):
    if isinstance(p,Point):
      return Line(self,p)
if __name__ == '__main__':
  p1 = Point(1,2)
  p2 = Point(2,3)
  #两个点相加 通过__add__方法
  line = p1 + p2 
  print l
  #>><__main__.Line instance at 0x02220738>
  #线减去一个点 通过__sub__方法
  print line - p1 
  #>><__main__.Point instance at 0x02220710>