Similar to the parsing tree example in class, there is not much usefulness in parsing and evaluating statements without an operator. Therefore, it is safe to assume that any input to your parsing tree will contain an operator.
Examples of valid inputs are:
- ( T AND F )
- ( ( T OR M_0.3 ) AND P_0.8 )
- ( P_0.9 OR M_0.4 )
Example of inputs that are not expected (and that you don’t need to account for):
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Also, if you haven’t started, and want a clean slate to start with, use this skeleton code in MS Teams: mp_parse.py (Links to an external site.)
What is the assignment?
- To implement functions to build, evaluate, and print expressions using our (made-up) maybe-probably logic
What to hand in?
- One (and only one) *.py file should be handed in. All your checks, unit tests should be inside of this file (similar to last assignment).
- Note that your program should be able to be run at console/terminal (e.g. $ python your_file.py). If it does not, then the execution portion of the assignment will be 0.
- Also note that you do not need to hand in binarytree.py nor stack.py; and you do *not* need to copy them into your file. Just import them. (For Peer Reviewers, ensure you put the code you will review in the same directory as
What needs to be done?
The primary tasks in this fourth assignment are to implement the following three functions.
1. buildMPLogicParseTree(s) – this function should take a string as input (e.g. s=”( T OR P_0.9 )”) and should return the binary tree representing the parse tree as described in class
2. evaluateMPLogicParseTree(t) – this function should take a binary tree as input and should return a T or an F that is based on the on the input statement
3. printMPLogicExpression(t) – this function should take a binary tree as input and should return the string that looks like the original string (perhaps with extra parentheses)
4. create some examples of how your functions work (inside of def main()), and test that each of the functions works correctly (using unittest)
Note: Those exact function names above should be used. If those name are not used 10pts will be automatically deducted.
- you should use the file parsetree.py for inspiration (located in MS Teams -> General -> Files -> Code); note: that file is for building entirely different types of parse trees so only parts of it will be relevant to this assignment
- you will also want to download the files binarytree.py and stack.py, and import them from your *.py file (all three files will need to exist in the same directory/folder)
- as with the last assignment, your *.py file will be run through a test script
When you submit your assignment, it will be graded in large part based on whether it successfully runs when using different input strings. The tests will roughy look like the following:
pt = buildMPLogicParseTree('( ( T AND F ) OR M_0.3 )')
ans = evaluateMPLogicParseTree(pt)
exp = printMPLogicExpression(pt)
# pt, ans, and exp will all be checked to ensure they are correct
Again, several different input strings will be also be tested.
When an M_x or P_x is present then the test will confirm that your tree evaluates to the correct average.
For example, the above input string will evaluate to T roughly 30% of the time.
What does maybe-probably logic look like again, exactly?
The symbols of our maybe-probably Boolean logic are:
- T – denotes True
- F – denotes False
- M_x is a maybe symboled that evaluates to true with probability x, 0.0 <= x <= 0.75 Ø
- P_x is a probably symbol that evaluates to true w/ probability x, 0.75 <= x < 1.0 Ø
- AND, OR – the two operators (note, these are binary operators)
- (, ) – parentheses are to be used in the same way as with the parse tree.py example we saw in class
Some additional examples of statements in this language are:
- ( T AND F ) a should evaluate to F for False
- ( T OR F ) a should evaluate to T for False
- ( M_0.7 ) a should evaluate to T for True 70% of the time
- ( M_0.9 ) invalid since parameter x is greater than 0.75!!
- ( ( P_0.8 AND T ) OR ( M_0.25 ) ) a should evaluate to true 85% of the time
As with other assignments, the final code should be your own work. However, discussing the general approach, or specific Python issues/functions, with others (e.g. on MSU Discord server), is acceptable, and encouraged! Of course, don’t hesitate to ask questions in MS Teams, by email, and in class. Again, note that the tree should include x, and that M_x or P_x terms should evaluate only inside of the evaluate function.