In my mind all Python variables are some kind of "named pointers", I find that
thinking this way helps me a lot in understanding what I'm doing. I know that
this is not completely technically correct as in the first two examples there
is actually a new a.i/a.arr created that shadows A.i, but thinking like this
helps me. Are there fundamental flaws to think this way?
Example:
>>>class A:
i = 0 ## Class A has a pointer named i pointing to (int 0 object)
## A.i -> (int 0 object)
>>>a = A() ## point a.i to the same thing A.i points to
## A.i -> (int 0 object)
## a.i -> (int 0 object)
>>>b = A() ## point b.i to the same thing A.i points to
## A.i -> (int 0 object)
## a.i -> (int 0 object)
## b.i -> (int 0 object)
>>>a.i = 1 ## point a.i to a new (int object)
## A.i -> (int 0 object)
## b.i -> (int 0 object)
## a.i -> (int 1 object)
>>>class A:
arr = [] ## A.i -> (empty list object)
>>>a = A() ## point a.arr to the same thing A.arr points to
## A.arr -> (empty list object)
## a.arr -> (empty list object)
>>>a.arr.append("haha") ## insert ("haha" string object) into (empty list
>>>object) both a.i and A.i point to
## A.i -> (list object) -> ("haha" string object)
## a.i -> (list object) -> ("haha" string object)
>>>a.arr = ["xixi"] ## point a.arr to a new (list object) pointing to a new
>>>("xixi" string object)
## A.i -> (list object) -> ("haha" string object)
## a.i -> (different list object) -> ("xixi" string
object)
>>>A.arr.append("xx") ## insert ("xx" string object) into (list object) A.i
>>>points to
## A.i -> (list object) -> ("haha" string object),("xx"
string object)
## a.i -> (different list object) -> ("xixi" string
object)
etc. ...
-------------------------------------
>>>class X:
def __init__(self):
self.arr = [] ## instances of Class X have a named pointer arr
pointing to a new (empty list object)
## X.arr does not exist!
>>>m = X() ## creates a new (empty list object) and has m.arr
>>>point to it
## m.arr -> (empty list object)
>>>n = X() ## creates a new (empty list object) and has n.arr
>>>point to it
## m.arr -> (empty list object)
## n.arr -> (different empty list object)
>>>m.arr.append("haha") ## insert ("haha" string object) into (list object) m.i
>>>points to
## m.i -> (list object) -> ("haha" string object)
## n.i -> (different empty list object)
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