Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Dutchling]

In Python, what is the difference between 'is' and 'is not', and '=' and '!='? Or are they the same?

[Mephisto]

In Python, what is the difference between 'is' and 'is not', and '=' and '!='? Or are they the same?

I'm horrible at explanations, but it's pretty easy to explain in code.

Warning: naive code. Don't do this. Breaks if the rhs of the equality check doesn't have an attribute named 'bar'.

Code: [Select]

>>> class Foo:
...     def __init__(self, bar):
...         self.bar = bar
...     def __eq__(self, other):
...         return self.bar == other.bar
>>> x = Foo(5)
>>> y = Foo(5)
>>> x == y
True
>>> x is y
False
>>> x is not y
True
>>> y = x
>>> x is y
True

Basically, is tests that both sides refer to the same object while == tests whatever __eq__ or __cmp__ methods you've defined.

[Dutchling]

So unless you use those they are the same? I tend to use 'is' and 'is not' with False, None, and True, but otherwise don't really use them.

[GlyphGryph]

Basically, "is" compares the internal object id, while "==" is just a regular method call that uses the defined "==" method for the object and returns the result.

[alexandertnt]

What would be the fastest way to draw isometric tiles in the correct order?

Currently I am using LINQ's OrderBy, which works, but is not very fast for large numbers of tiles...

[Nadaka]

What would be the fastest way to draw isometric tiles in the correct order?

Currently I am using LINQ's OrderBy, which works, but is not very fast for large numbers of tiles...

Why are you using an OrderBy when you could be using a 2 dimensional array?

[MagmaMcFry]

What would be the fastest way to draw isometric tiles in the correct order?

Currently I am using LINQ's OrderBy, which works, but is not very fast for large numbers of tiles...

Why are you using an OrderBy when you could be using a 2 dimensional array?

This here. Remember, view distance ordering only needs to be correct when the tiles overlap (I'm assuming you're using a grid). So you can just draw them in 2d array reading order, as long as you start with the furthest tile.

[miauw62]

@Dutchling

If a is b and a = 5, b == 5 too.
If you add 3 to a, a == 8, and b == 8.

You get this situation if you define b by doing a = b.

(I don't actually remember how to assign b the value of a without causing this.)

[Dutchling]

@Dutchling

If a is b and a = 5, b == 5 too.
If you add 3 to a, a == 8, and b == 8.

You get this situation if you define b by doing a = b.

(I don't actually remember how to assign b the value of a without causing this.)

That's not necessarily right and also not something I was wondering about

Code: [Select]

>>> a = 5
>>> b = a
>>> a += 3
>>> b
5But

Code: [Select]

>>> class CLASS():
True


>>> a = CLASS()
>>> b = a
>>> a.five = 5
>>> b.five
5
>>> a.five += 3
>>> b.five
8

[miauw62]

Welp, fuck me

[SethCreiyd]

In Python, the referenced value of an int is changed when you increment it.  When you have a line like ' x = 5; y = x ', what it means to the interpreter is, 'Make a new int object named x and assign it this literal value, then make a new object named y with a reference to the same value as x.'

The line ' x += 1 ' means 'Change the reference of x to a value equal to the current referenced value plus one.'

Code: [Select]

>>> a = int(255)
>>> b = 255
>>> a += 1
>>> a is b
False
>>> b += 1
>>> a is b
True

>>> # int(a) is int(b) only if (a == b <= 256).
>>> a += 1; b += 1
>>> a is b
False
>>> n = 57
>>> id(57), id(n)
(5393408, 5393408)  # same object
>>> n = 257
>>> id(257), id(n)
(38467464, 38467476)  # different objects

In the CLASS example, by assigning a.five you're changing a value referenced by both a and b.  b is not its own CLASS instance, it's a reference to the same instance that was created with 'a = CLASS()'.  b.five is a.five because b is a.

Code: [Select]

>>> a = SomeClass()
>>> a.text = "I am referenced by a."
>>> b = a
>>> b.text += " I am also referenced by b."
>>> a.text
'I am referenced by a. I am also referenced by b.'


[Dutchling]

Which is why I use a class for my global variables/constants :V

[alexandertnt]

What would be the fastest way to draw isometric tiles in the correct order?

Currently I am using LINQ's OrderBy, which works, but is not very fast for large numbers of tiles...

Why are you using an OrderBy when you could be using a 2 dimensional array?

This here. Remember, view distance ordering only needs to be correct when the tiles overlap (I'm assuming you're using a grid). So you can just draw them in 2d array reading order, as long as you start with the furthest tile.

I forgot to mention that the world is 3d (x, y, z) and certain objects may exist between tiles.

[Rose]

3D doesn't complicate things.  Stonesense is 3D and does the drawing pretty easily.

It's the objects between tiles that complicate things.

[alexandertnt]

3D doesn't complicate things.  Stonesense is 3D and does the drawing pretty easily.

Do you mean easily as in "easy to code" or easy as in "runs fast"?