Artificial Intelligence (CS 5300/CS 6300)

CS 5300/CS 6300 Frequently Asked Questions

Graphics won't work in pacman.py under CADE!
If you get an error that says something about "No module named _tkinter", then please follow the instructions below. Basically what happened is the CADE opers remove the Tcl/Tk (graphics) support this semester and I didn't notice!
I've installed a copy of Tcl/Tk and Python 2.6 in the ~cs5350 directory (yes, 5350, not 5300: this is because I have a much larger quota in 5350 than 5300 and this stuff wouldn't fit in 5300).
First, you need to set your library path so that it looks in the ~cs5350/lib directory for dynamic libraries. If you're running a csh-style shell, you'll need to say setenv LD_LIBRARY_PATH /home/cs5350/lib:$LD_LIBRARY_PATH; if you're using a bash-style shell, you'll need to say export LD_LIBRARY_PATH=/home/cs5350/lib:$LD_LIBRARY_PATH. (You can check which shell you're running by saying echo $SHELL.) Note, if you don't currently have a LD_LIBRARY_PATH defined, remove the ":$LD_LIBRARY_PATH" from these expressions (the shell will complain about an undefined variable in this case).
Next, when you invoke python, you'll need to run the version in ~cs5350/bin/python. This is version 2.6. So, for instance, you can run pacman with: ~cs5350/bin/python pacman.py if you're in the search directory.
It's probably a bit of a pain to do this every time, so here's some stuff to do it automatically. If you're running a csh shell, then you'll want to add the following two lines to your .cshrc file that's in your home directory:
```
setenv LD_LIBRARY_PATH /home/cs5350/lib:$LD_LIBRARY_PATH
alias python /home/cs5350/bin/python
```
On the other hand, if you're running a bash shell, you'll want to add the following lines to your .bashrc file that's in your home directory:
```
export LD_LIBRARY_PATH=/home/cs5350/lib:$LD_LIBRARY_PATH
alias python='/home/cs5350/bin/python'
```
Again, if you don't currently have a LD_LIBRARY_PATH defined, remove the ":$LD_LIBRARY_PATH" from these expressions (the shell will complain about an undefined variable in this case when you log back in).
Now, you should just be able to log out from CADE, log back in, and run pacman via:
```
python pacman.py
```
without any extra magic.
Do I have to use CADE?
You do not have to do your development on CADE machines. You are free to develop on your own machine (Mac, Windows, Linux, etc.). However, we need to run your code, which we will do on CADE machines. So for safety's sake, it's probably best if you try to run your code at least a few times on the CADE machines before submitting it. CADE has a good set of FAQs on doing remote access.
Python and Indentation
Since Python is sensitive to indentation, it's important to keep the indentation consistent across functions and methods. One common error is to use spaces as indentation for one function and then use tabs elsewhere; this will result in a fairly cryptic compiler error. To avoid this, we recommend against using tabs for indentation, or to set you editor to use soft tabs,
I wrote a function in filename.py. How do I execute it from the Python interpreter?
If you start Python from the same directory that filename.py is in (or if it's in the Python path...), then you can import the contents of filename.py as a module:
>>> import filename >>> filename.function(arguments)
With this kind of import statement, you must reference the module name followed by the function name. Alternatively, you can import the contents of filename.py into the local namespace:
>>> from filename import * >>> function(arguments)
With this kind of import statement, you no longer need to reference the module name.
Why are dictionary keys in such a strange order? Should I worry about the order?
Dictionaries in Python (like HashMaps in Java) are implemented using hash tables. The order of the keys depends on how exactly the hashing algorithm maps keys to buckets, and will usually seem arbitrary. Your code should not rely on key ordering, and you should not be surprised if even a small modification to how your code uses a dictionary results in a new key ordering.
Problem:
ImportError: No module named py

Solution:
When using import, do not include the ".py" from the filename.
For example, you should say: import shop
NOT: import shop.py
Problem:
NameError: name 'MY VARIABLE' is not defined
Even after importing you may see this.

Solution:
To access a member of a module, you have to type MODULE NAME.MEMBER NAME, where MODULE NAME is the name of the .py file, and MEMBER NAME is the name of the variable (or function) you are trying to access.
Problem:
TypeError: 'dict' object is not callable

Solution:
Dictionary looks up are done using square brackets: [ and ]. NOT parenthesis: ( and ).
Problem:
ValueError: too many values to unpack

Solution:
Make sure the number of variables you are assigning in a for loop matches the number of elements in each item of the list. Similarly for working with tuples.
For example, if pair is a tuple of two elements (e.g. pair =('apple', 2.0)) then the following code would cause the "too many values to unpack error":
(a,b,c) = pair

Here is a problematic scenario involving a for loop:
```
pairList = [('apples', 2.00), ('oranges', 1.50), ('pears', 1.75)]
for fruit, price, color in pairList:
    print '%s fruit costs %f and is the color %s' % (fruit, price, color)
```
Problem:
AttributeError: 'list' object has no attribute 'length' (or something similar)

Solution:
Finding length of lists is done using len(NAME OF LIST).
Problem:
Changes to a file are not taking effect.

Solution:
1. Make sure you are saving all your files after any changes.
2. If you are editing a file in a window different from the one you are using to execute python, make sure you reload(YOUR_MODULE) to guarantee your changes are being reflected. reload works similar to import.