Programming Guidelines

Style Suggestions

• Comment your code -- it really makes a difference, not only to others trying to understand your code, but to you when you're trying to debug it.
• Name your variables meaningfully. A variable named  "threshold" versus "x" makes code much easier to read.
• Simple or Compound Statements

There are many ways to write software.  You can separate each step in a calculation on a separate line and assign it to variables, or you can combine everything on one line.  It all amounts to readability.

Take this example of a compound statement, which computes a convective / total precipitation ratio, then creates a boolean grid which is based on total precipitation from 0 to 0.02", and then creates a grid with ProbPrecip values if there is precipitation (precipMask) and the ratio (precipRatio) is less than 10%:

        precipRatio = cp_SFC / (tp_SFC + 0.0001)
        precipMask = logical_and(greater(tp_SFC, 0.0), less(tp_SFC, 0.02*25.4))
        grid = where(logical_and(precipMask, less(precipRatio, 0.1)), ProbPrecip, 0.0)

This same code fragment may be written in the following way. The precipRatio is the calculated cp/tp ratio; precipPositive is a boolean grid where tp > 0; precipLess2 is a boolean grid where tp < 0.02" (which includes zero); precipBetweenZeroAnd2 is a boolean grid where tp > 0 and tp < 0.02"; precipRatioLess10 is a boolean grid where the precipRatio is less than 10%, precipRatioAndLowPrecip is a boolean grid where tp > 0 and less than 0.02", and where the cp/tp ratio is less than 0.1:

        precipRatio = cp_SFC / (tp_SFC + 0.0001)
        precipPositive = greater(tp_SFC, 0.0)
        precipLess2 = less(tp_SFC, 0.02*25.4)
        precipBetweenZeroAnd2 = logical_and(precipPositive, precipLess2)
        precipRatioLess10 = less(precipRatio, 0.1)
        precipRatioAndLowPrecip = logical_and(precipRatioLess10, precipBetweenZeroAnd2)
        grid = where(precipRatioAndLowPrecip, ProbPrecip, 0.0)

The second fragment, though longer, is composed of simpler statements and is easier to follow and read.  Note also, that we have named the variables to reflect the concepts and improve readability.

Trouble-shooting Ideas

•  Error Messages:   Make sure you are running the GFE from a terminal window so that you will see any Python error messages that occur when you run your  Smart  Tool or Procedure. These messages will give line numbers and descriptions that help you trace the origin of the problem.
•  Print Statements:  Using the Python "print" statement within your Smart Tool or Procedure is one of the quickest ways to determine where a problem is occurring and what might be causing it.  Simply interspersing "progress" statements such as the following throughout your tool can help:

         Here are some other example "print" statements:

           print "myVariable =",   myVariable

           # To print Python Numeric array information:
           print   "Dimensions of array T:",  T.shape,   "Value of T at point 20, 20: ", T[20][20]

• Simplify:  If the problem is within a complicated method, simplify it by commenting out the code and gradually introducing pieces of it.  Go back to something you know works and then start adding functionality to it.