visibility between modules

[max(01)*]

hi.

if i have a single program file, different class instances can share
information in (at least) two fashions:

1. using instance variables:

class AClass:
def __init__(self):
self.att_1 = 42
self.att_2 = "Hello!"

class AnotherClass:
def __init__(self):
self.att_1 = anInstanceOfACl ass.att_1

anInstanceOfACl ass = AClass()
anInstanceOfAno therClass = AnotherClass()
print anInstanceOfAno therClass.att_1 ### This should print out 42

2. using globals:

class AClass:
def __init__(self):
self.att_1 = 42
self.att_2 = "Hello!"

class AnotherClass:
pass

aGlobalString = "No way."
anInstanceOfACl ass = AClass()
anInstanceOfACl ass.att2 = aGlobalString
anInstanceOfAno therClass = AnotherClass()
anInstanceOfAno therClass.att_1 = aGlobalString
print anInstanceOfACl ass.att2 ### This should output "No way."
print anInstanceOfAno therClass.att_1 ### And this too

----

i admit i prefer the fisrt way to do it. i have tried to make it work
even if the "main program" and each class definition reside in different
files, but i could not make it work:

max2@172.17.1.2 01:/tmp$ cat AClass.py
class AClass:
def __init__(self):
self.att_1 = 42
self.att_2 = "Hello!"
max2@172.17.1.2 01:/tmp$ cat AnotherClass.py
class AnotherClass:
def __init__(self):
self.att_1 = anInstanceOfACl ass.att_1
max2@172.17.1.2 01:/tmp$ cat Main.py
from AClass import *
from AnotherClass import *
anInstanceOfACl ass = AClass()
anInstanceOfAno therClass = AnotherClass()
print anInstanceOfAno therClass.att_1 ### This should print out 42
max2@172.17.1.2 01:/tmp$ python Main.py
Traceback (most recent call last):
File "Main.py", line 4, in ?
anInstanceOfAno therClass = AnotherClass()
File "/tmp/AnotherClass.py ", line 3, in __init__
self.att_1 = anInstanceOfACl ass.att_1
NameError: global name 'anInstanceOfAC lass' is not defined
max2@172.17.1.2 01:/tmp$

----

any suggestion?

bye max

[Mike Meyer]

Re: visibility between modules

"max(01)*" <max2@fisso.cas a> writes:
[color=blue]
> hi.
>
> if i have a single program file, different class instances can share
> information in (at least) two fashions:
>
> 1. using instance variables:
>
> class AClass:
> def __init__(self):
> self.att_1 = 42
> self.att_2 = "Hello!"
>
> class AnotherClass:
> def __init__(self):
> self.att_1 = anInstanceOfACl ass.att_1
>
> anInstanceOfACl ass = AClass()
> anInstanceOfAno therClass = AnotherClass()
> print anInstanceOfAno therClass.att_1 ### This should print out 42
>
> 2. using globals:
>
> class AClass:
> def __init__(self):
> self.att_1 = 42
> self.att_2 = "Hello!"
>
> class AnotherClass:
> pass
>
> aGlobalString = "No way."
> anInstanceOfACl ass = AClass()
> anInstanceOfACl ass.att2 = aGlobalString
> anInstanceOfAno therClass = AnotherClass()
> anInstanceOfAno therClass.att_1 = aGlobalString
> print anInstanceOfACl ass.att2 ### This should output "No way."
> print anInstanceOfAno therClass.att_1 ### And this too[/color]


Both these methods actually use globals. In ther first case, the
global is "anInstanceOfAC lass", that is bound to self.att_1 in the
__init__ method of AnotherClass.

The solution is to pass the instance in as a parameter:

class AClass:
def __init__(self):
self.att_1 = 42
self.att_2 = "Hello!"

class AnotherClass:
def __init__(self, instance):
sefl.att_1 = instance

anInstanceOfACl ass = AClass()
anInstanceOfAno therClass = AnotherClass(an InstanceOfAClas s)

or maybe just:

anInstaceOfAnot herClass = AnotherClass(AC lass())


<mike
--
Mike Meyer <mwm@mired.or g> http://www.mired.org/home/mwm/
Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information.