refering to base classes

[glenn]

hi - Im quite new to python, wondering if anyone can help me understand
something about inheritance here. In this trivial example, how could I
modify the voice method of 'dog' to call the base class 'creatures'
voice method from with in it?

class creature:
def __init__(self):
self.noise=""
def voice(self):
return "voice:" + self.noise

class dog(creature):
def __init__(self):
self.noise="bar k"

def voice(self):
print "brace your self:"

thanks
glenn

[Chaz Ginger]

Re: refering to base classes

glenn wrote:

hi - Im quite new to python, wondering if anyone can help me understand
something about inheritance here. In this trivial example, how could I
modify the voice method of 'dog' to call the base class 'creatures'
voice method from with in it?
>
class creature:
def __init__(self):
self.noise=""
def voice(self):
return "voice:" + self.noise
>
class dog(creature):
def __init__(self):
self.noise="bar k"
>
def voice(self):
print "brace your self:"
>
thanks
glenn
>

Try this:

class dog(creature):
.....
def voice(self):
print "brace your self:"
creature.voice( self)

This should do it.

[Chaz Ginger]

Re: refering to base classes

Chaz Ginger wrote:

glenn wrote:

>hi - Im quite new to python, wondering if anyone can help me understand
>something about inheritance here. In this trivial example, how could I
>modify the voice method of 'dog' to call the base class 'creatures'
>voice method from with in it?
>>
>class creature:
> def __init__(self):
> self.noise=""
> def voice(self):
> return "voice:" + self.noise
>>
>class dog(creature):
> def __init__(self):
> self.noise="bar k"
>>
> def voice(self):
> print "brace your self:"
>>
>thanks
>glenn
>>

Try this:
>
class dog(creature):
.....
def voice(self):
print "brace your self:"
creature.voice( self)
>
This should do it.

I did forget to mention that in 'dog"s' __init__ you had better call
creature's __init__. You might make it look like this:

def __init__(self):
self.noise = 'bark'
creature.__init __(self)

There is another approach - using Superclass - but I will leave that
exercise to the reader.

[Roberto Bonvallet]

Re: refering to base classes

glenn wrote:

[...] In this trivial example, how could I modify the voice method of
'dog' to call the base class 'creatures' voice method from with in it?
>
class creature:
def __init__(self):
self.noise=""
def voice(self):
return "voice:" + self.noise
>
class dog(creature):
def __init__(self):
self.noise="bar k"
>
def voice(self):
print "brace your self:"

If you want dog.voice() to just print "voice: bark", you just have to omit
the voice method for the dog class: it will be inherited from creature.

If you want dog.voice() to do something else, you can call superclass'
method like this:

def voice(self):
creature.voice( self)
print "brace your self"
any_other_magic ()

HTH
--
Roberto Bonvallet

[Bruno Desthuilliers]

Re: refering to base classes

glenn wrote:

hi - Im quite new to python, wondering if anyone can help me understand
something about inheritance here. In this trivial example, how could I
modify the voice method of 'dog' to call the base class 'creatures'
voice method from with in it?
>
class creature:
def __init__(self):
self.noise=""
def voice(self):
return "voice:" + self.noise
>
class dog(creature):
def __init__(self):
self.noise="bar k"
>
def voice(self):
print "brace your self:"

<ot>
It might be better to use newstyle classes if you can. Also, the
convention is to use CamelCase for classes names (unless you have a
strong reason to do otherwise).
</ot>

Here you could use a class attribute to provide a default:

class Creature(object ):
noise = ""

def voice(self):
return "voice:" + self.noise


class Dog(Creature):
noise="bark"

def voice(self):
print "brace your self:"
return Creature.voice( self)
# can also use this instead, cf the Fine Manual
return super(Dog, self).voice()

My 2 cents
--
bruno desthuilliers
python -c "print '@'.join(['.'.join([w[::-1] for w in p.split('.')]) for
p in 'onurb@xiludom. gro'.split('@')])"

[Jason]

Re: refering to base classes

Chaz Ginger wrote:

Chaz Ginger wrote:

glenn wrote:

hi - Im quite new to python, wondering if anyone can help me understand
something about inheritance here. In this trivial example, how could I
modify the voice method of 'dog' to call the base class 'creatures'
voice method from with in it?
>
class creature:
def __init__(self):
self.noise=""
def voice(self):
return "voice:" + self.noise
>
class dog(creature):
def __init__(self):
self.noise="bar k"
>
def voice(self):
print "brace your self:"

>
I did forget to mention that in 'dog"s' __init__ you had better call
creature's __init__. You might make it look like this:
>
def __init__(self):
self.noise = 'bark'
creature.__init __(self)
>

There's a problem with Chaz's __init__() method. Notice that the
creature class's __init__ sets self.noise to the empty string. In this
case, the superclass's __init__() method should be called first:

class dog(creature):
def __init__(self):
creature.__init __(self)
self.noise = "bark"
def voice(self):
print "brace your self:"
creature.voice( self)

--Jason

[Chaz Ginger]

Re: refering to base classes

Jason wrote:

Chaz Ginger wrote:

>Chaz Ginger wrote:

>>glenn wrote:
>>>hi - Im quite new to python, wondering if anyone can help me understand
>>>something about inheritance here. In this trivial example, how could I
>>>modify the voice method of 'dog' to call the base class 'creatures'
>>>voice method from with in it?
>>>>
>>>class creature:
>>> def __init__(self):
>>> self.noise=""
>>> def voice(self):
>>> return "voice:" + self.noise
>>>>
>>>class dog(creature):
>>> def __init__(self):
>>> self.noise="bar k"
>>>>
>>> def voice(self):
>>> print "brace your self:"

>I did forget to mention that in 'dog"s' __init__ you had better call
>creature's __init__. You might make it look like this:
>>
>def __init__(self):
> self.noise = 'bark'
> creature.__init __(self)
>>

>
There's a problem with Chaz's __init__() method. Notice that the
creature class's __init__ sets self.noise to the empty string. In this
case, the superclass's __init__() method should be called first:
>
class dog(creature):
def __init__(self):
creature.__init __(self)
self.noise = "bark"
def voice(self):
print "brace your self:"
creature.voice( self)
>
--Jason
>

Very true....I was showing him in "spirit only"...lol.


Chaz.

[glenn]

Re: refering to base classes


Chaz Ginger wrote:

Chaz Ginger wrote:

glenn wrote:

hi - Im quite new to python, wondering if anyone can help me understand
something about inheritance here. In this trivial example, how could I
modify the voice method of 'dog' to call the base class 'creatures'
voice method from with in it?
>
class creature:
def __init__(self):
self.noise=""
def voice(self):
return "voice:" + self.noise
>
class dog(creature):
def __init__(self):
self.noise="bar k"
>
def voice(self):
print "brace your self:"
>
thanks
glenn
>

Try this:

class dog(creature):
.....
def voice(self):
print "brace your self:"
creature.voice( self)

This should do it.

I did forget to mention that in 'dog"s' __init__ you had better call
creature's __init__. You might make it look like this:
>
def __init__(self):
self.noise = 'bark'
creature.__init __(self)
>
There is another approach - using Superclass - but I will leave that
exercise to the reader.

first tip worked - funny thing was I =thought= I done that, but clearly
not - so thanks was going mad.
Superclass?... ok will look into this
thanks for reply(s)
Glenn

[glenn]

Re: refering to base classes


Bruno Desthuilliers wrote:

glenn wrote:

hi - Im quite new to python, wondering if anyone can help me understand
something about inheritance here. In this trivial example, how could I
modify the voice method of 'dog' to call the base class 'creatures'
voice method from with in it?

class creature:
def __init__(self):
self.noise=""
def voice(self):
return "voice:" + self.noise

class dog(creature):
def __init__(self):
self.noise="bar k"

def voice(self):
print "brace your self:"

>
>
<ot>
It might be better to use newstyle classes if you can. Also, the
convention is to use CamelCase for classes names (unless you have a
strong reason to do otherwise).
</ot>
>
Here you could use a class attribute to provide a default:
>
class Creature(object ):
noise = ""
>
def voice(self):
return "voice:" + self.noise
>
>
class Dog(Creature):
noise="bark"
>
def voice(self):
print "brace your self:"
return Creature.voice( self)
# can also use this instead, cf the Fine Manual
return super(Dog, self).voice()
>
My 2 cents

ohh - interesting. Thanks for the camelCase tip - dont have a good
reason to do otherwise, just bad habits.
so for your $.02 do you see this as being, umm, superior in anyway to
creature.voice( )?

glenn

--
bruno desthuilliers
python -c "print '@'.join(['.'.join([w[::-1] for w in p.split('.')]) for
p in 'onurb@xiludom. gro'.split('@')])"

[glenn]

Re: refering to base classes

Hi Roberto

If you want dog.voice() to just print "voice: bark", you just have to omit
the voice method for the dog class: it will be inherited from creature.
>

I would have thought this would be correct, but in this case, plus in
others im playin with, I get this issue:
-----------------------
given animal.py is:
class creature:
def __init__(self):
self.noise=""
def voice(self):
return "voice:" + self.noise

class dog(creature):
def __init__(self):
self.noise="bar k"

then I get this outcome...

>>>import animal
>>beagle=animal .dog
>>beagle.voice( )

Traceback (most recent call last):
File "<input>", line 1, in ?
TypeError: unbound method voice() must be called with dog instance as
first argument (got nothing instead)

>>>

------------------------
So I guess it wants something in position of self?

any idea what Im doing wrong? - this would be very handy as its a point
Im stymied on a couple of 'projects'
thanks
Glenn

If you want dog.voice() to do something else, you can call superclass'
method like this:
>
def voice(self):
creature.voice( self)
print "brace your self"
any_other_magic ()
>

HTH
--
Roberto Bonvallet

[Ben Finney]

Naming conventions (was: Re: refering to base classes)

"glenn" <glenn@tangelos oftware.netwrit es:

Bruno Desthuilliers wrote:

It might be better to use newstyle classes if you can. Also, the
convention is to use CamelCase for classes names (unless you have
a strong reason to do otherwise).

Note that this style is more correctly called TitleCase, since the
first letter of *every* word is capitalised, like in a headline (or
title). "camel case" is different -- see below.

ohh - interesting. Thanks for the camelCase tip - dont have a good
reason to do otherwise, just bad habits.

The style called camelCase (all words run together, capitalise first
letter of every word except the first) is prevalent in Java, where it
denotes the name of an *instance*, in contrast to a *class* which is
named with TitleCase.

The camelCase style is less popular in the Python world, where (as per
PEP 8) instances are named with all lower case, either joinedwords or
separate_by_und erscores.

--
\ "Crime is contagious ... if the government becomes a |
`\ lawbreaker, it breeds contempt for the law." -- Justice Louis |
_o__) Brandeis |
Ben Finney

[Steve Holden]

Re: refering to base classes

glenn wrote:

Hi Roberto
>

>>If you want dog.voice() to just print "voice: bark", you just have to omit
>>the voice method for the dog class: it will be inherited from creature.
>>

>
I would have thought this would be correct, but in this case, plus in
others im playin with, I get this issue:
-----------------------
given animal.py is:
class creature:
def __init__(self):
self.noise=""
def voice(self):
return "voice:" + self.noise
>
class dog(creature):
def __init__(self):
self.noise="bar k"
>
then I get this outcome...
>

>>>>import animal
>>>>beagle=anim al.dog

[...]

Shouldn't that be

beagle = animal.dog()

to create an instance?

We've all done it ...

regards
Steve
--
Steve Holden +44 150 684 7255 +1 800 494 3119
Holden Web LLC/Ltd http://www.holdenweb.com
Skype: holdenweb http://holdenweb.blogspot.com
Recent Ramblings http://del.icio.us/steve.holden

[Bruno Desthuilliers]

Re: Naming conventions

Ben Finney wrote:

"glenn" <glenn@tangelos oftware.netwrit es:
>

>Bruno Desthuilliers wrote:

>>It might be better to use newstyle classes if you can. Also, the
>>convention is to use CamelCase for classes names (unless you have
>>a strong reason to do otherwise).

>
Note that this style is more correctly called TitleCase, since the
first letter of *every* word is capitalised, like in a headline (or
title). "camel case" is different -- see below.

Oops, sorry - my mistake.

--
bruno desthuilliers
python -c "print '@'.join(['.'.join([w[::-1] for w in p.split('.')]) for
p in 'onurb@xiludom. gro'.split('@')])"

[Bruno Desthuilliers]

Re: refering to base classes

glenn wrote:

Bruno Desthuilliers wrote:
>

(snip)

>>
>Here you could use a class attribute to provide a default:
>>
>class Creature(object ):
> noise = ""
>>
> def voice(self):
> return "voice:" + self.noise
>>
>>
>class Dog(Creature):
> noise="bark"
>>
> def voice(self):
> print "brace your self:"
> return Creature.voice( self)
> # can also use this instead, cf the Fine Manual
> return super(Dog, self).voice()
>>

(snip)

so for your $.02 do you see this as being, umm, superior in anyway to
creature.voice( )?

I suppose "this" refers to the use of super() ? If so, I wouldn't say
it's "superior", but it can be helpful with complex inheritence scheme
(something that does'nt happen very frequently in Python), and more
specifically with multiple inheritance. You may want to read this for
more infos:

http://www.python.org/download/releases/2.2.3/descrintro/#mro

HTH
--
bruno desthuilliers
python -c "print '@'.join(['.'.join([w[::-1] for w in p.split('.')]) for
p in 'onurb@xiludom. gro'.split('@')])"

[glenn]

Re: refering to base classes

>

Shouldn't that be
>
beagle = animal.dog()
>
to create an instance?
>
We've all done it ...

lol - actually Im confused about this - there seem to be cases where
instantiaing with:
instance=module .classname()
gives me an error, but
instance=module .classname
doesnt - so I got into that habit, except for where I had a constructor
with parameters - except now Im feeling foolish because I cant
replicate the error - which suggests I didnt understand the error
message properly in the first place... arrgh
I guess thats just part of the process of gaining a new language.

glenn