Drilling down in a dict with "complex" objects

[Six]

I am trying to access an objects sub-object attributes. I can boil the
code I am working with down to this problem section:
(snip)
class Pt:
x = None
y = None
def __init__(self, x, y):
self.x, self.y = x, y
pass

class Pts:
curr_point = None
next_point = None
def __init__(self, n, m):
self.next_point = Pt(n, m)
def update(self, point):
self.curr_point = self.next_point
self.next_point = point

class PtManage:
points = {}
def __init__(self):
pass

point = Pts(3,5)
pman = PtManage()
pman.points["odds"] = point
print dir(pman)

print pman["odds"].next_point.x

(snip)

It's this last line that doesn't work. What am I doing wrong? Is this
a failure of the design or am I missing something obvious? How do I
get down and see that "Pt" classes x attribute within the PtManage
dict?

 

[Sean DiZazzo]

I am trying to access an objects sub-object attributes. I can boil the
code I am working with down to this problem section:
(snip)
class Pt:
  x = None
  y = None
  def __init__(self, x, y):
    self.x, self.y = x, y
  pass

class Pts:
  curr_point = None
  next_point = None
  def __init__(self, n, m):
    self.next_point = Pt(n, m)
  def update(self, point):
    self.curr_point = self.next_point
    self.next_point = point

class PtManage:
  points = {}
  def __init__(self):
    pass

point = Pts(3,5)
pman = PtManage()
pman.points["odds"] = point
print dir(pman)

print pman["odds"].next_point.x

(snip)

It's this last line that doesn't work. What am I doing wrong? Is this
a failure of the design or am I missing something obvious? How do I
get down and see that "Pt" classes x attribute within the PtManage
dict?

Don't you mean?

pman.points["odds"].next_point.x

 

[Benjamin Kaplan]

I am trying to access an objects sub-object attributes. I can boil the
code I am working with down to this problem section:
(snip)
class Pt:
 x = None
 y = None
 def __init__(self, x, y):
   self.x, self.y = x, y
 pass

class Pts:
 curr_point = None
 next_point = None

First of all, don't do this. Python doesn't have variable
declarations, only assignments. So this creates a variable called
curr_point for the *class*, not for the instance. What Java calls
static variables. It doesn't matter here but...

 def __init__(self, n, m):
   self.next_point = Pt(n, m)
 def update(self, point):
   self.curr_point = self.next_point
   self.next_point = point

class PtManage:
 points = {}

Here you have a single mutable dict shared by all instances of PtManage.
a = PtManage()
b = PtManage()
a.points["a"] = Pts(3,2)
print b.points

 def __init__(self):
   pass

point = Pts(3,5)
pman = PtManage()
pman.points["odds"] = point
print dir(pman)

print pman["odds"].next_point.x

PtManage doesn't define __getitem__, so pman["odds"] won't work.
pman.points["odds"] should.

 

[Terry Reedy]

[snip]
It's this last line that doesn't work. What am I doing wrong?

When posting such questios, print the traceback if there is one or
otherwise describe 'does not work' in much more detail.

 

[Chris Rebert]

I am trying to access an objects sub-object attributes. I can boil the
code I am working with down to this problem section:
(snip)
class Pt:
 x = None
 y = None
 def __init__(self, x, y):
   self.x, self.y = x, y
 pass

class Pts:
 curr_point = None
 next_point = None
 def __init__(self, n, m):
   self.next_point = Pt(n, m)
 def update(self, point):
   self.curr_point = self.next_point
   self.next_point = point

class PtManage:
 points = {}
 def __init__(self):
   pass

point = Pts(3,5)
pman = PtManage()
pman.points["odds"] = point
print dir(pman)

print pman["odds"].next_point.x

(snip)

It's this last line that doesn't work. What am I doing wrong? Is this
a failure of the design or am I missing something obvious? How do I
get down and see that "Pt" classes x attribute within the PtManage
dict?

I suggest you read the part of Python's tutorial concerning classes
(http://docs.python.org/tutorial/classes.html ). Note that "curr_point
= None" and similar at the class level *does not* declare an object
field, because Python does not have instance variable declarations.
Here is a fixed and normalized version of the classes in your example:

class Pt(object):
def __init__(self, x, y):
self.x, self.y = x, y

class Pts(object):
def __init__(self, n, m):
self.curr_point = None
self.next_point = Pt(n, m)
def update(self, point):
self.curr_point = self.next_point
self.next_point = point

class PtManage(object):
def __init__(self):
self.points = {}


As for why your last line fails:

print pman["odds"].next_point.x

As Sean said, you're missing a ".points":
print pman.points["odds"].next_point.x

Also, is there any reason for PtManage over just using a `points`
dictionary directly?

Cheers,
Chris