Using for-loops for cursors

When writing Python scripts to automate ArcGIS you often encounter all kind of cursors. Cursors are returned mostly returned by the gp object when calling functions like listtables, listfeatureclasses, listrasters, listfields, searchcursor, updatecursor, ... Usually cursors are used in the following way :

    import arcgisscripting
    gp = arcgisscripting.create()
    inputFC = r'path to a feature class'

    inRows = gp.searchcursor(inputFC)
    inRow = inRows.next()
    while inRow:
        ...do something
    inRow = inRows.next()

This is quiet a verbose way to loop through the rows. Fortunately there is a way to turn the cursor into an iterator that can be used in a for loop. This can be done by adding the following short class to your code.

    class CursorIterator(object):
        def __init__(self, cursor):
            self.cursor = cursor
            self.cursor.reset()
        def next(self):
            n = self.cursor.next()
            if n is None:
                self.cursor.reset()
                raise StopIteration
            return n
        def __iter__(self):
            return self

As it is nicely explained in Expert Python Programming by Tarek Ziadé we just created an iterator class. This is a container class with two methods namely next and __iter__. Usage of the CursorIterator class looks like this.

    rows = gp.searchcursor(inputFC)
    rowsIterator = CursorIterator(rows)
    for row in rowsIterator:
        ... do something

or shorter

    for row in CursorIterator(gp.searchcursor(inputFC)):
        ... do something

I hope you enjoyed my first post. Have fun.

Update : As Jason Schreider points out in his comment the CursorIterator class can be easily replaced by the following :

    rows = gp.searchcursor(inputFC)
    for row in iter(rows.next, None):
        ... do something