truth table: Nullary and Unary Operations

questions about Nullary and Unary Operations

Here are questions you can answer after going through this chapter

what are the Nullary Operations?
How many inputs do Nullary Operations take?
what are the Unary Operations?
How many inputs do Unary Operations take?
what is a function that returns its input as output?
what is a function that returns the negation of its input?
how can I return the opposite of a boolean?

requirements

truth table

Nullary Operations

There are 2 Nullary operations - Logical True and Logical False. They do NOT take input and return True or False

test_logical_true

RED: make it fail

I change the class and method in test_truth_table.py

import unittest
import src.truth_table

class TestNullaryOperations(unittest.TestCase):

    def test_logical_true(self):
        self.assertTrue(src.truth_table.logical_true())

# Exceptions seen

the terminal shows AttributeError

AttributeError: module 'src.truth_table' has no attribute 'logical_true'

I have not added a definition for logical_true to truth_table.py in the src folder

GREEN: make it pass

I add it to the list of Exceptions seen in test_truth_table.py

# Exceptions seen
# AssertionError
# AttributeError

I open truth_table.py from the src folder in the editor of my Integrated Development Environment (IDE), then I add a function
```
1def logical_true():
2    return None
```
the terminal shows AssertionError
```
AssertionError: None is not true
```
I change None to True in the return statement
```
1def logical_true():
2    return True
```
the test passes
Adding the logical_true function to truth_table.py solved the AttributeError
logical_true always returns True
logical_true does not take any input

test_logical_false

RED: make it fail

I add another test in test_truth_table.py

    def test_logical_true(self):
        self.assertTrue(src.truth_table.logical_true())

    def test_logical_false(self):
        self.assertFalse(src.truth_table.logical_false())


# Exceptions seen

the terminal shows AttributeError

AttributeError: module 'src.truth_table' has no attribute 'logical_false'. Did you mean: 'logical_true'?

I have not added a definition for logical_false to truth_table.py, I only added one for logical_true

GREEN: make it pass

I add a function definition in truth_table.py

def logical_true():
    return True


def logical_false():
    return True

the terminal shows AssertionError

AssertionError: True is not false

I change True to False in the return statement
```
5def logical_false():
6    return False
```
the test passes
Adding the logical_true and logical_falsefunction to truth_table.py solved the AttributeError in both cases
logical_true always returns True
logical_false always returns False
both Nullary Operations do not take input

Unary Operations

There are 2 unary operations

Logical Identity and
Logical Negation

they each take one input and return True or False

test_logical_identity

RED: make it fail

I add a new TestCase and a test for Unary Operations to test_truth_table.py

    def test_logical_false(self):
        self.assertFalse(src.truth_table.logical_false())

class TestUnaryOperations(unittest.TestCase):

    def test_logical_identity(self):
        self.assertTrue(src.truth_table.logical_identity(True))

# Exceptions seen

the terminal shows AttributeError

AttributeError: module 'src.truth_table' has no attribute 'logical_identity'

I need to add a definition for it

GREEN: make it pass

I add the function to truth_table.py

def logical_false():
    return False


def logical_identity():
    return False

the terminal shows TypeError

TypeError: logical_identity() takes 0 positional arguments but 1 was given

I need to make the function accept input since the test sends True as input

I add the error to the list of Exceptions seen in test_truth_table.py

# Exceptions seen
# AssertionError
# AttributeError
# TypeError

I add a name in parentheses for logical_identity to take input in truth_table.py

def logical_identity(the_input):
    return False

the terminal shows AssertionError

AssertionError: False is not true

I change the return statement

def logical_identity(the_input):
    return True

the test passes

REFACTOR: make it better

I add another line to test_logical_identity in test_truth_table.py for the case when logical_identity gets False as input

    def test_logical_identity(self):
        self.assertTrue(src.truth_table.logical_identity(True))
        self.assertFalse(src.truth_table.logical_identity(False))

the terminal shows AssertionError

AssertionError: True is not false

I change the return statement of logical_identity in truth_table.py
```
 9def logical_identity(the_input):
10    return False
```
the terminal shows AssertionError
```
AssertionError: False is not true
```
there is a failure for the test that passed before. The expectation of the test is that when True is given, the result is True and when False is given, the result is False

I change the return statement of the function

def logical_identity(the_input):
    return the_input

the test passes.

logical_identity returns its input as output. I think of it as a passthrough function, it does not do anything with what it gets, it only passes it along.

test_logical_negation

RED: make it fail

I add a new test to test_truth_table.py for logical_negation

    def test_logical_identity(self):
        self.assertTrue(src.truth_table.logical_identity(True))
        self.assertFalse(src.truth_table.logical_identity(False))

    def test_logical_negation(self):
        self.assertFalse(src.truth_table.logical_negation(True))


# Exceptions seen

the terminal shows AttributeError

AttributeError: module 'src.truth_table' has no attribute 'logical_negation'

GREEN: make it pass

I add a definition for the function in truth_table.py

def logical_identity(the_input):
    return the_input


def logical_negation(the_input):
    return the_input

the terminal shows AssertionError

AssertionError: True is not false

I change the return statement

def logical_negation(the_input):
    return False

the test passes

REFACTOR: make it better

I add another line to test_logical_negation in test_truth_table.py

    def test_logical_negation(self):
        self.assertFalse(src.truth_table.logical_negation(True))
        self.assertTrue(src.truth_table.logical_negation(False))

the terminal shows AssertionError

AssertionError: False is not true

I change the return statement of the logical_negation function in truth_table.py
```
13def logical_negation(the_input):
14    return True
```
the terminal shows AssertionError
```
AssertionError: True is not false
```
the test fails for the line that passed before
I make the function return its input, remember the identity function
```
13def logical_negation(the_input):
14    return the_input
```
the terminal shows AssertionError
```
AssertionError: True is not false
```
the expectation of the test is that when True is given, the result is False and when False is given, the result is True

how to return the opposite of a boolean

I can make this happen with the “not” keyword which returns the opposite of the boolean after it. I add it to the return statement
```
13def logical_negation(the_input):
14    return not the_input
```
the test passes

I change the name of the test

class TestUnaryOperations(unittest.TestCase):

    def test_logical_identity(self):
        self.assertTrue(src.truth_table.logical_identity(True))
        self.assertFalse(src.truth_table.logical_identity(False))

    def test_logical_negation_aka_not(self):
        self.assertFalse(src.truth_table.logical_negation(True))
        self.assertTrue(src.truth_table.logical_negation(False))


# Exceptions seen

logical_negation also known as not returns the opposite of its input

when it receives True it returns False
when it receives False it returns True

close the project

I close test_truth_table.py and truth_table.py in the editor
I click in the terminal and use q on the keyboard to leave the tests and the terminal goes back to the command line
I change directory to the parent of truth_table
```
cd ..
```
the terminal shows
```
.../pumping_python
```
I am back in the pumping_python directory

review

I ran the following tests for Nullary

test_logical_true
test_logical_false

and

for Unary operations

test_logical_identity
test_logical_negation

How many questions can you answer after going through this chapter?

code from the chapter

Do you want to see all the CODE I typed for the Truth Table?

what is next?

Would you like to test binary operations?

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truth table

truth table: Binary Operations 1