Not Defined error in basic code

[Calvin Spealman]

A few notes, Jack:

On Thu, Mar 14, 2019 at 10:32 AM Jack Dangler <tdldev at gmail.com> wrote:

>
> On 3/14/19 10:11 AM, Calvin Spealman wrote:
>
> Where are you seeing something like this? The two lines under `class
> weapon:` are not correct because they are variable names that you've never
> defined.
>
> Maybe you intended this to "declare" the attributes for the class? That
> isn't something you need to do in Python. If you simply remove these lines
> your example should work.
>
> On Thu, Mar 14, 2019 at 10:05 AM Jack Dangler <tdldev at gmail.com> wrote:
>
>> Just getting started with tutorials and such, and don't understand this -
>>
>> <file: class_weapon.py>
>>
>> class weapon:
>>      weaponId
>>      manufacturerName
>>
>>      def printWeaponInfo(self):
>>          infoString = "ID: %d Mfg: %s Model: %s" % (self.weaponId,
>> self.manufacturerName)
>>          return infoString
>>
>> <file: weaponTrack.py>
>>
>> import class_weapon
>>
>> MyWeapon=weapon()
>> MyWeapon.weaponId = 100
>> MyWeapon.manufacturerName = "Glock"
>>
>> print(MyWeapon.printWeaponInfo)
>>
>> executing 'python3 weaponTrack.py' results in this bailing on the first
>> element in the class with "not defined". I've been staring at templates
>> of this exact structure for about an hour trying to figure out why this
>> isn't running at all. Is it simply because it isn't all in one file?
>> Thanks for any guidance. Really appreciate the help.
>>
>>
>> Thanks.
>>
>> --
>> https://mail.python.org/mailman/listinfo/python-list
>>
>
>
> --
>
> CALVIN SPEALMAN
>
> SENIOR QUALITY ENGINEER
>
> cspealma at redhat.com  M: +1.336.210.5107
> <https://red.ht/sig>
> TRIED. TESTED. TRUSTED. <https://redhat.com/trusted>
>
> Calvin
>
> Thank you for the reply. I tried defining them in the form of 'int
> weaponId' but that didn't help. I finally put it in this form 'weaponId=0"
> and it liked that. So, i updated the class file to be as follows -
>
> <file: class_weapon.py>
>
> class weapon:
>      weaponId=0
>      manufacturerName=""
>
Technically this will work, but it won't always work. You're assigning
these values directly to the class (or type) and not to individual objects
of that type.

This will break very badly if you try to do this with any type of value
that can be changed (like a list, which you can add things to) because
you'll accidentally
modify values shared between ALL objects of the same type. Instead, you
want to define a __init__ method, which is called when all objects of this
type are
created, and assign the attributes in there. Like this:

def __init__(self):
    self.weaponId = 0
    self.manufacturerName = ""

Of course, you could make it easier to create the specific objects you want
by passing parameters at the creation of the object:

def __init__(self, weaponId, manufacturerName):
    self.weaponId = weaponId
    self.manufacturerName = manufacturerName

     def printWeaponInfo(self):
>          infoString = "ID: %d Mfg: %s " % (self.weaponId,
> self.manufacturerName)
>          return infoString
>
> The second file now looks like this -
>
> <file: weaponTrack.py>
>
> import class_weapon
> MyWeapon=class_weapon.weapon
> MyWeapon.weaponId = 100
> MyWeapon.manufacturerName = "Glock"
>
If you follow my advice above, you won't need to override the values here.

But you aren't actually creating anything here, because this line:

MyWeapon = class_weapon.weapon

Doesn't create anything. It just assigns the class you made to a new name.
What you probably meant to do, and can do with the
__init__ I suggest above, is create an instance of your weapon class like
this:

MyWeapon = class_weapon.weapon(100, "Glock")

>
> print(MyWeapon.printWeaponInfo)
>
Similarly, you probably meant to call this method but without parenthesis
on the method you just printed the object representing
the method itself, rather than calling it and printing the value it returns.

print(MyWeapon.printWeaponInfo())

> so now, when I run 'python3 weaponTrack.py', I get <function
> weapon.printWeaponInfo at 0x7f2bd3ae7510>, but am expecting
>
> ID: 100 Mfg: Glock ...
>
I hope this helps.

-- 

CALVIN SPEALMAN

SENIOR QUALITY ENGINEER

cspealma at redhat.com  M: +1.336.210.5107
<https://red.ht/sig>
TRIED. TESTED. TRUSTED. <https://redhat.com/trusted>