Learning new stuff

For the past couple of weeks I’m  (re)learning a couple of web frameworks. Namely, Yii for PHP and jQuery for JavaScript.

Almost always, my process when learning something new goes like this:

1. Find an introductory tutorial or book to get a glimpse of what is possible and get a feeling of how it all works.
2. Establish a robust source of documentation, which, at least for OSS stuff, will most probably be the guide found on the developers’ site.
3. Play around with it. For me that almost always means “Make a simple game with it”

And this is what I came up with jQuery after just 2-3 days of getting serious about it:

http://pastehtml.com/view/b6ih9wnt2.html 😉

Such a great and easy framework!!

All code is embedded in the HTML in case you want to take a look.

Nick

Python Object Reference

I have a friend struggling with some code wight now, so I’m copy-pasting an interactive session with some object reference basics that I hope will clarify some things 😉

There’s also a pastie for this in http://paste.lisp.org/+2E0W for easier reading.

>>> # First, lets make a Class to help with tests
>>> class Coco(object):
	def __init__(self, value=0):
		self.value = value

>>> # Lets make a list of instances, the dumb way
>>> a = [Coco()] * 4
>>> a
[<__main__.Coco object at 0xb64c9cac>, <__main__.Coco object at 0xb64c9cac>,
 <__main__.Coco object at 0xb64c9cac>, <__main__.Coco object at 0xb64c9cac>]

>>> # See that the addresses are the same? Lets look values
>>> [i.value for i in a]
[0, 0, 0, 0]

>>> # Now, let's try to change one of them
>>> a[0].value = 1

>>> # We now expect [1, 0, 0, 0], right?
>>> [i.value for i in a]
[1, 1, 1, 1]

>>> # NOPE! All of them changed because it's THE SAME OBJECT
>>> 

>>> # Let's do it again the smart way
>>> a = []
>>> for i in range(4):
	a.append(Coco())

>>> a
[<__main__.Coco object at 0xb64b906c>, <__main__.Coco object at 0xb64d128c>,
 <__main__.Coco object at 0xb64d1c2c>, <__main__.Coco object at 0xb64d1c0c>]

>>> # See that the addresses are different?
>>> [i.value for i in a]
[0, 0, 0, 0]

>>> a[0].value = 1
>>> [i.value for i in a]
[1, 0, 0, 0]

>>> # Pretty cool huh?
>>> 

>>> # Lets also put the list in variable b
>>> b = a
>>> [i.value for i in a]
[1, 0, 0, 0]

>>> [i.value for i in b]
[1, 0, 0, 0]

>>> # And change a value in b
>>> b[0].value = 0
>>> [i.value for i in b]
[0, 0, 0, 0]
>>> [i.value for i in a]
[0, 0, 0, 0]
>>> # a and b are the same object. A no brainer!
>>> 

>>> # Now let's copy once with copy() and once with deepcopy()
>>> from copy import copy, deepcopy
>>> a_copy = copy(a) # You can also do =a[:] for lists and =a.copy() for dicts
>>> a_deepcopy = deepcopy(a)
>>> a
[<__main__.Coco object at 0xb64b906c>, <__main__.Coco object at 0xb64d128c>,
 <__main__.Coco object at 0xb64d1c2c>, <__main__.Coco object at 0xb64d1c0c>]

>>> a_copy
[<__main__.Coco object at 0xb64b906c>, <__main__.Coco object at 0xb64d128c>,
 <__main__.Coco object at 0xb64d1c2c>, <__main__.Coco object at 0xb64d1c0c>]

>>> a_deepcopy
[<__main__.Coco object at 0xb64d1a4c>, <__main__.Coco object at 0xb64d1a2c>,
 <__main__.Coco object at 0xb64d1a0c>, <__main__.Coco object at 0xb64d19ec>]

>>> a_copy[0].value = 4
>>> a_deepcopy[1].value = 6
>>> # Can you foretell what will happen now?
>>> [i.value for i in a_copy]
[4, 0, 0, 0]

>>> [i.value for i in a_deepcopy]
[0, 6, 0, 0]

>>> [i.value for i in a]
[4, 0, 0, 0]

>>> # While a and a_copy are not the same, their contents are shared!
>>> # Here's how to try when in doubt
>>> a is b
True

>>> a is a_copy
False

>>> a[0] is a_copy[0]
True

>>> a[0] is a_deepcopy[0]
False

>>>
>>> # PS. If you make a list the dumb way
>>> a = [Coco()] * 4

>>> # ..you'll have a list of the same objects even after a deepcopy
>>> k = [Coco()] * 4
>>> k_deepcopy = deepcopy(k)
>>> k_deepcopy[0].value = 1
>>> [i.value for i in k_deepcopy]
[1, 1, 1, 1]

>>> k_deepcopy[0] is k_deepcopy[3]
True

>>> # ..although, not the same ones as the originals
>>> [i.value for i in k]
[0, 0, 0, 0]

>>> k_deepcopy[0] is k[0]
False

>>>
>>> # Hope that's helpful ;)
>>>

Nick