Metaprogramming

ILists

Module to provide an ‘intelligent’ list class

ILists are useful, if you have a number of simular objects, on which you would like to access the same properties and store these properties in a new list, which basically means:

IList.<name> == IList([obj.<name> for obj in IList])

Example

>>> l = IList([complex(3, 4), complex(6)])
>>> l.real
[3.0, 6.0]

You can also use callable attributes of your objects:

>>> l = IList([complex(3, 4), complex(6)])
>>> l
[(3+4j), (6+0j)]
>>> l.conjugate()
[(3-4j), (6-0j)]

You can add callbacks, for appending and removing objects. These callbacks must accept two positional arguments - the list and the object. The callbacks are called _after_ executing append or remove:

>>> def on_append(l, x):
...     print("Adding %s to %s." % (x, l))
>>> def on_remove(l, x):
...     print("Removing %s from %s." % (x, l))
>>> l = IList(on_append=on_append, on_remove=on_remove)
>>> l.append(3)
Adding 3 to [3].
>>> l.remove(3)
Removing 3 from [].
>>> def invalid_callback(l):
...     print(l)
>>> l = IList(on_append=invalid_callback)
Traceback (most recent call last):
...
TypeError: on_append and on_remove must accept 2 positional arguments
>>> l = IList(on_append=3)
Traceback (most recent call last):
...
TypeError: on_append and on_remove must accept 2 positional arguments

>>> def valid_callback(l=[], x=5):
...     pass
>>> def valid_callback2(l, x=5, y=3):
...     pass
>>> l = IList(on_append=valid_callback, on_remove=valid_callback2)

ILists implement the __abs__ special method:

>>> l = IList([complex(3, 4), complex(6)])
>>> abs(l)
[5.0, 6.0]

Be aware, that only attribute names, that are not used by the list class are overwritten, so if list implemented a attribute name, you can’t use it with ILists (unless you subclass them and overwrite the attribute name). The following code doesn’t work, because list implements ‘__add__’ (so the result is NOT [4, 5] as one could expect):

>>> l = IList([1, 2])
>>> l + 3
Traceback (most recent call last):
...
TypeError: can only concatenate list (not "int") to list

class mtoolbox.ilist.IList(iterable=None, on_append=None, on_remove=None)

Bases: list

‘intelligent’ list object

Parameters:

• iterable (iterable) – The
• on_append (callable) – callback(list, item) for append()
• on_remove (callable) – callback(list, item) for remove()

Returns:

An IList instance

Return type:

IList

Note

Both callbacks must accept two positional arguments

append(obj)

Add obj to IList

Parameters:obj (object) – object to append to list Returns:None

Usage:

>>> l = IList()
>>> l
[]
>>> l.append(3)
>>> l
[3]

remove(obj)

Remove obj from IList

Parameters:obj (object) – object to remove from list Returns:None

Usage:

>>> l = IList([8])
>>> l
[8]
>>> l.remove(8)
>>> l
[]
>>> l.remove(6)
Traceback (most recent call last):
...
ValueError: list.remove(x): x not in list