105 lines
4.6 KiB
HTML
105 lines
4.6 KiB
HTML
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<html>
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<title>GFESuite Documentation - Python Programming Guidelines</title>
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<body>
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<h1 align=center>
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<a NAME="Guidelines"></a>Programming Guidelines</h1>
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<div CLASS="2Heading"> <a href="#StyleSuggestions">Style
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Suggestions</a></div>
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<div CLASS="2Heading"> <a href="#Trouble-shootingIdeas">Trouble-shooting
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Ideas</a></div>
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<hr width="100%">
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<h2 align=center>
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<a NAME="StyleSuggestions"></a>Style Suggestions</h2>
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<ul>
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<li>
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Comment your code -- it really makes a difference, not only to others trying
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to understand your code, but to you when you're trying to debug it.</li>
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<li>
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Name your variables meaningfully. A variable named "threshold"
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versus "x" makes code much easier to read.</li>
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<li>
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Simple or Compound Statements</li>
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<br>There are many ways to write software. You can separate each
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step in a calculation on a separate line and assign it to variables, or
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you can combine everything on one line. It all amounts to readability.
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<p>Take this example of a compound statement, which computes a convective
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/ total precipitation ratio, then creates a boolean grid which is based
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on total precipitation from 0 to 0.02", and then creates a grid with ProbPrecip
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values if there is precipitation (precipMask) and the ratio (precipRatio)
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is less than 10%:
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<p><tt> precipRatio = cp_SFC
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/ (tp_SFC + 0.0001)</tt>
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<br><tt> precipMask = logical_and(greater(tp_SFC,
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0.0), less(tp_SFC, 0.02*25.4))</tt>
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<br><tt> grid = where(logical_and(precipMask,
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less(precipRatio, 0.1)), ProbPrecip, 0.0)</tt>
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<p>This same code fragment may be written in the following way. The precipRatio
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is the calculated cp/tp ratio; precipPositive is a boolean grid where tp
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> 0; precipLess2 is a boolean grid where tp < 0.02" (which includes
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zero); precipBetweenZeroAnd2 is a boolean grid where tp > 0 and tp <
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0.02"; precipRatioLess10 is a boolean grid where the precipRatio is less
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than 10%, precipRatioAndLowPrecip is a boolean grid where tp > 0 and less
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than 0.02", and where the cp/tp ratio is less than 0.1:
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<p><tt> precipRatio = cp_SFC
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/ (tp_SFC + 0.0001)</tt>
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<br><tt> precipPositive = greater(tp_SFC,
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0.0)</tt>
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<br><tt> precipLess2 = less(tp_SFC,
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0.02*25.4)</tt>
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<br><tt> precipBetweenZeroAnd2
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= logical_and(precipPositive, precipLess2)</tt>
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<br><tt> precipRatioLess10 =
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less(precipRatio, 0.1)</tt>
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<br><tt> precipRatioAndLowPrecip
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= logical_and(precipRatioLess10, precipBetweenZeroAnd2)</tt>
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<br><tt> grid = where(precipRatioAndLowPrecip,
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ProbPrecip, 0.0)</tt>
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<p>The second fragment, though longer, is composed of simpler statements
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and is easier to follow and read. Note also, that we have named the
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variables to reflect the concepts and improve readability.</ul>
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<h2 align=center>
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<a NAME="Trouble-shootingIdeas"></a>Trouble-shooting Ideas</h2>
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<ul>
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<li>
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Error Messages: Make sure you are running the GFE from
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a terminal window so that you will see any Python error messages that occur
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when you run your Smart Tool or Procedure. These messages will
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give line numbers and descriptions that help you trace the origin of the
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problem.</li>
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<li>
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Print Statements: Using the Python "print" statement within
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your Smart Tool or Procedure is one of the quickest ways to determine where
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a problem is occurring and what might be causing it. Simply interspersing
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"progress" statements such as the following throughout your tool can help:</li>
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</ul>
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print "Made it to this point"
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<p> Here are some other
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example "print" statements:
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<p> print "myVariable
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=", myVariable
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<p> # To print
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Python Numeric array information:
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<br> print
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"Dimensions of array T:", T.shape, "Value of T at point
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20, 20: ", T[20][20]
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<ul>
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<li>
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Simplify: If the problem is within a complicated method, simplify
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it by commenting out the code and gradually introducing pieces of it.
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Go back to something you know works and then start adding functionality
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to it.</li>
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</ul>
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</div>
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</body>
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</html>
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