I'm trying to call a method in a class. I don't know what 'self' refers to, and what is the correct procedure to call such a method inside a class and outside a class.
Could someone explain how to call the move
method with the variable RIGHT
?
The following class works in Scott's Python script which is accessed by a terminal GUI (urwid).
The function I'm working with is a Scott Weston's missile launcher Python script, which I'm trying to hook into a PHP web-server.
class MissileDevice:
INITA = (85, 83, 66, 67, 0, 0, 4, 0)
INITB = (85, 83, 66, 67, 0, 64, 2, 0)
CMDFILL = ( 8, 8,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0)
STOP = ( 0, 0, 0, 0, 0, 0)
LEFT = ( 0, 1, 0, 0, 0, 0)
RIGHT = ( 0, 0, 1, 0, 0, 0)
UP = ( 0, 0, 0, 1, 0, 0)
DOWN = ( 0, 0, 0, 0, 1, 0)
LEFTUP = ( 0, 1, 0, 1, 0, 0)
RIGHTUP = ( 0, 0, 1, 1, 0, 0)
LEFTDOWN = ( 0, 1, 0, 0, 1, 0)
RIGHTDOWN = ( 0, 0, 1, 0, 1, 0)
FIRE = ( 0, 0, 0, 0, 0, 1)
def __init__(self, battery):
try:
self.dev=UsbDevice(0x1130, 0x0202, battery)
self.dev.open()
self.dev.handle.reset()
except NoMissilesError, e:
raise NoMissilesError()
def move(self, direction):
self.dev.handle.controlMsg(0x21, 0x09, self.INITA, 0x02, 0x01)
self.dev.handle.controlMsg(0x21, 0x09, self.INITB, 0x02, 0x01)
self.dev.handle.controlMsg(0x21, 0x09, direction+self.CMDFILL, 0x02, 0x01)
The first argument of all methods is usually called self
. It refers to the instance for which the method is being called.
Let's say you have:
class A(object):
def foo(self):
print('Foo')
def bar(self, an_argument):
print('Bar', an_argument)
Then, doing:
a = A()
a.foo() #prints 'Foo'
a.bar('Arg!') #prints 'Bar Arg!'
There's nothing special about this being called self
, you could do the following:
class B(object):
def foo(self):
print('Foo')
def bar(this_object):
this_object.foo()
Then, doing:
b = B()
b.bar() # prints 'Foo'
In your specific case:
dangerous_device = MissileDevice(some_battery)
dangerous_device.move(dangerous_device.RIGHT)
(As suggested in comments MissileDevice.RIGHT
could be more appropriate here!)
You could declare all your constants at module level though, so you could do:
dangerous_device.move(RIGHT)
This, however, is going to depend on how you want your code to be organized!