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CS1 Python Subgoals

Section 2.16 Assign Booleans

Subgoals for evaluating an assignment statement.

  1. Decide order of operations
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    1. Decompose as necessary
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  2. Determine operator behavior based on operands
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    1. Operator and operands must be compatible
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  3. Solve arithmetic, expression, or operation
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    1. Decompose as necessary
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Subsection 2.16.1

Given the following code snippet, evaluate the final statement (the last line). If invalid, give the reason. If valid, what value is assigned to the variable?
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alpha = 42
beta = 1
gamma = 5
result = beta <= alpha
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Subsection 2.16.2 SG1: Decide order of operations

There is only a single operator, the <= (less than or equal to operator), so that is the only one that needs to be evaluated.
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Subsection 2.16.3 SG2: Determine operator behavior based on operands

The <= operator will determine if one value is less than or equal than the other, and requires that they be compatible types. Integers and floats are compatible with each other, but in this case both alpha and beta are integers, which are definitely compatible. The result will be a boolean value.
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Subsection 2.16.4 SG3: Solve arithmetic, expression, or operation

First, beta is substituted for 1 and alpha is substituted for 42. Then, the <= determines if 1 is less than or equal to 42, which it is. Therefore, the expression evaluates to True, which is assigned to the variable result.
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Subsection 2.16.5 Questions to check understanding

  1. If the > operator was used, would the result still be a boolean variable?
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    Answer.
    Yes, any comparison operator used on two integers will produce a boolean (although that value could be either True or False).
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  2. If alpha was a float, would the result still be a boolean variable?
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    Answer.
    Yes, the comparison operators allow you to combine integers and floats, and the result will still be a boolean value.
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