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  1. PO
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    <p>When I run your code, the stack trace I get is:</p> <pre><code>Traceback (most recent call last): File "md.py", line 22, in &lt;module&gt; analyze_the_shape([(0, 0), (0, 4.0), (4.0, 4.0), (4.0, 0)]) File "md.py", line 18, in analyze_the_shape angle = math.degrees(math.acos(cos_angle)) ValueError: math domain error </code></pre> <p>I know <code>math.acos</code> only accepts values such that <code>-1.0 &lt;= x &lt;= 1.0</code>. If I print out <code>cos_angle &lt; -1.0</code> right before the line <code>angle = math.degrees(math.acos(cos_angle))</code>, it prints <code>True</code>. If I print out <code>cos_angle</code>, it prints <code>-1.0</code>.</p> <p>I'm guessing the issue here is that the way Python stores <code>cos_angle</code> isn't perfect, and that the value you generate for <code>cos_angle</code> is just barely less than <code>-1.0</code>.</p> <p>Perhaps it would be better, if, instead of checking <code>abs(angle - 90.0) &lt; 0.001</code>, you checked if <code>abs(cos_angle) &lt; 0.001</code>.</p> <p><strong>Edit</strong>:</p> <p>I think you have an error in this line:</p> <pre><code>cos_angle = float((hypo**2 - (d3)**2 + (d4)**2) / ((-2.0)*(d4)*(d3))) </code></pre> <p>It probably should be:</p> <pre><code>cos_angle = float((hypo**2 - ((d3)**2 + (d4)**2)) / ((-2.0)*(d4)*(d3))) </code></pre> <p>Note the extra parens around <code>(d3)**2 + (d4)**2</code>. This makes sure that addition is done <em>before</em> you subtract that quantity from <code>hypo**2</code>.</p>
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    1. POWhy do I get ValueError : math domain error?
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    1. USSam Mussmann
    1. USSam Mussmann
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    1. CO`abs(angle - 90.0) < 0.001` and `abs(cos_angle + 1) < 0.001` do not mean the same. If `angle=90`, `cos_angle=0`. If `cos_angle=-1`, `angle=180`.
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      1. USJulien Vivenot
    2. COGood catch! I think there's an error where the OP sets `cos_angle` -- I've pointed that out in my answer.
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      1. USSam Mussmann
    3. CO"the way Python stores `cos_angle` isn't perfect". This should the "the way floating point numbers are represented on a computer is not perfect, and thus computational errors are unavoidable". Python has absolutely nothing to do with this.
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      1. USBakuriu
 

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