PyChecker does STATIC analysis?

[Skip Montanaro]

    beliavsky> If I run PyChecker on the following program, stored in xtry.py, 

    beliavsky> m = 10000000
    beliavsky> k = 0
    beliavsky> for i in xrange(m):
    beliavsky>     k = k + i
    beliavsky> print k
    beliavsky> x = range(3)
    beliavsky> print x[3]

    beliavsky> the output is

    beliavsky> 49999995000000

    beliavsky> Warnings...

    beliavsky> xtry:1: NOT PROCESSED UNABLE TO IMPORT
    ...

    beliavsky> I am surprised that PyChecker actually needs to execute the
    beliavsky> code block

    beliavsky> for i in xrange(m):
    beliavsky>     k = k + i
    beliavsky> print k

    beliavsky> before finding the out-of-bounds error. 

Try modifying your code to this:

    if __name__ == "__main__":
        m = 10000000
        k = 0
        for i in xrange(m):
            k = k + i
        print k
        x = range(3)
        print x[3]

PyChecker simply imports your module.  Importing a module causes the code at
the top level to be executed.

    beliavsky> The Lahey/Fujitsu Fortran 95 compiler is able to catch the
    beliavsky> out-of-bounds error at COMPILE time for an analogous Fortran
    beliavsky> program.

Python is just slightly more dynamic than Fortran, and I'm sure the
Lahey/Fujitsu compiler has had a few more man-years of development put into
it than PyChecker.  As an example of the former point, note that PyChecker
can't assume that the output of range(3) is a list of 3 elements.  Another
module may have modified builtins before the code was executed.

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