Python loop seems not to be iterating

Question

The below code is not acting as expected for me.

class stateClass:
  state = 0

states = []
states.append(stateClass)
states.append(stateClass)

def populateStates(states):
  for s in states:
    if s.state == 0
      print 'populating'
      s.state = 1

populateStates(states)

the output is

states array length: 2
populating

this is failing the second time

for s in states:
  if s.state == 0

if conditional is failing the second time although it is a different index in the array and thus the s.state should have been initialized to 0. So I think the loop is not iterating properly.

Anyone know whats wrong?

You are adding the class, not instances to the array. Do you really want this? — user647772
– user647772, Commented Sep 10, 2012 at 10:53

Jon Clements · Accepted Answer · 2012-09-10 11:06:47Z

6

You don't need the ;'s - this isn't C and co. etc...

class stateClass: 
    state = 0

Here you're creating a class level attribute - ie, state is shared by all instances of stateClass.

You're appending to your list stateClass itself - ie, the definition of the class, not an actual instance of a class...

As soon as you change state in one of them, all instances of stateClass now have that changed value.

You most likely want to be creating instances:

class State(object):
    def __init__(self, number):
        self.state = number

Hawaii = State(50)  
Kentucky = State(23) # (making state numbers up here...) 

my_states = []
my_states.append(Hawaii)
my_states.append(Kentucky)

To then show state, do something like:

print Hawaii.state

If you wanted a property so it avoids explicit setting from outside the class then:

class State(object):
    def __init__(self, number):
        self._state = number
    @property
    def state(self):
        return self._state

edited Sep 10, 2012 at 11:06

answered Sep 10, 2012 at 10:54

Jon Clements

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1 Comment

Eoin Murray Over a year ago

How do I access the elements of the state then after initialisation? Hawaii.number isnt working for me?

Daniel Roseman · Accepted Answer · 2012-09-10 10:53:38Z

5

Python is not Java. The loop is fine, the problem is the class.

state is a class variable, not an instance variable. It is shared by all instances of the class. And you're not actually instantiating the class at all.

Do this instead:

class stateClass(object):
  def __init__(self):  
    self.state = 0

states.append(stateClass())

And you don't need the semicolons.

answered Sep 10, 2012 at 10:53

Daniel Roseman

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