arcpy Array methods

Question

Has anyone else had problems with the Array class? I'm trying to do a sort on line segments that I have stored as arrays of points. All the Array methods seem to work fine except for insert and clone. Every time I use the insert method it appends.

Also does anybody have a working example of how to use the clone method?

KimOllivier · Answer

Maybe it is because we are all too casual with the difference between immutable and mutable objects in Python. The arrays are mutable, so assigning a new value does not work as expected.
# classic example of mutabilty in action
a = ['spam', 'eggs', 100, 1234]
b = a
b.append("abc")

print a
# ['spam','eggs',100,1234,'abc'] # << note that a is altered when we only appended to b
print b
# ['spam','eggs',100,1234,'abc']

RobFlemming · Answer

Another bug, I think:

import arcpy
p = arcpy.Point()
a = arcpy.Array()
a.add(p)
a.add(p)
a.add(p)
p.X=11
a.replace(0,p) #so far so good
p.X=12
a.replace(2,p) #but, they are both replaced
p2 = arcpy.Point() #however, if you make a new point...
p2.X=42
a.replace(2,p2)#...it goes only where expected

If you change an attribute of an existing point object, even the id, and then replace it somewhere, it will replace all the old instances in the array with the new attribute.
(So maybe it's not a bug?)
(just a little annoying)

Anonymous User · Answer

The only workaround I've found is to redraw the array of point arrays in the order I want. I know that the Array insert and replace methods expect a point or array object, and the clone method expects a point object. I can only think that the problem is that these methods aren't accepting the parameters as array or point objects, even though I built the arrays using arcpy.Array(), array.add(), and pntArray.add(), and I've built the points using arcpy.Point(). I'm passing the objects based as addresses retrieved by using the getObject method. It almost seems like the methods will only accept static objects and not dynamic objects, but isn't the array just a set of pointers?