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Use of update() for an instantiated object – Artificial Intelligence

I apologize in advance if I’m asking a somewhat obvious question, but I’m somewhat new to Python and am still figuring out the kinks of it.

I’m working on a script to search through a tree, starting at node A and (hopefully) terminating at goal node M. My work is based off of the example code provided in Artificial Intelligence: A Modern Approach, specifically this Python search script.

I run into difficulties when attempting to execute a breadth_first_search, where I get the following error:

...
update(self, state=state, parent=parent, action=action, 
        path_cost=path_cost, depth=0)
NameError: global name 'update' is not defined

I am attempting to use the update() function to update the state, parent, children, etc. of a node, where the code is as follows:

class Node:

    def __init__(self, state, parent=None, action=None, path_cost=0):
        "Create a search tree Node, derived from a parent by an action."
        update(self, state=state, parent=parent, action=action, 
                path_cost=path_cost, depth=0)
        if parent:
            self.depth = parent.depth + 1

I’ve been stuck on this for a while now and am unsure how to proceed. I would greatly appreciate any suggestions to help fix this problem. Thank you!

Tags:

4

Answers


  1. 0

    The link you have given for update is not a global function, but a member of dictionary, so must be called on a dictionary. If your class had one, called e.g. data

    def __init__(self, state, parent=None, action=None, path_cost=0):
    "Create a search tree Node, derived from a parent by an action."
    self.data.update(state=state, parent=parent, action=action, path_cost=path_cost, depth=0)
    # Note the indentation

    Edit

    Furthermore, not the code you link to also has a utils.py here
    This defines a global update function that will do what Node is trying to do:

    def update(x, **entries):
    """Update a dict; or an object with slots; according to entries.
    >>> update({'a': 1}, a=10, b=20)
    {'a': 10, 'b': 20}
    >>> update(Struct(a=1), a=10, b=20)
    Struct(a=10, b=20)
    """
    if isinstance(x, dict):
        x.update(entries)
    else:
        x.__dict__.update(entries)
    return x

    You probably need to get the whole svn repo, with their directory structure in order to get this working.

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  2. 0

    update() is a method of the builtin dict type. Note the section under which that method’s documentation resides. If you were using a dictionary, let’s call it my_dict, you’d do something like this:

    my_dict.update(state=state, parent=parent, action=action, path_cost=path_cost, depth=0)

    But I’m not sure you are using a dictionary for your code. The link you posted does not define the update() function. It must be imported with the line at the top of the example code:

    from utils import *

    This assumes that in utils.py there is a function named update. If that’s the case, you need to include that import statement in your file.

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  3. 0

    update() is an instance method for dictionary objects. Unless you define the same method for your Node:

    class Node:

    ...

    def update(self, ...)

    have a dictionary within the class that can be updated:

    class Node:

    def __init__(self, ...):
        ...
        self.some_dict.update(...)

    or create or import a function that takes a Node object:

    def update(node, ...)

    it will not be available.

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  4. 0

    The update() function you linked is a method of the dict type. If your object is a subclass of dict ( or a subclass of a subclass ), you should be able to call

    self.update()
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