Re: Do I need self and other?
In article [EMAIL PROTECTED], Kurda Yon [EMAIL PROTECTED] wrote: Hi, I found one example which defines the addition of two vectors as a method of a class. It looks like that: class Vector: def __add__(self, other): data = [] for j in range(len(self.data)): data.append(self.data[j] + other.data[j]) return Vector(data) In this example one uses self and other. Does one really need to use this words? And, if yes, why? I have replaced self by x and other by y and everything looks OK. Is it really OK or I can have some problem in some cases? What everyone else has said: yes and no. Having said that, it seems to me like this is exactly the sort of situation where 'x' and 'y' make a lot of sense - self means that this is the object on which the method was invoked, and here that seems irrelevant: If you want to calculate x + y you use x.data and y.data... Otoh, I once saw a library (someone's Python arbitrary-precision reals package) where he used x and y, and sure enough I was confused. Otooh, I was't confused by it for long, and I quickly decided that it actually made _that_ code look like it made more sense. Thank you! -- David C. Ullrich -- http://mail.python.org/mailman/listinfo/python-list
Re: Do I need self and other?
On Fri, 27 Jun 2008 20:19:00 -0400, Nick Dumas [EMAIL PROTECTED] wrote: [snip] Example: class Foo(): self.x = 5 Have you tried what you're posting? Python 2.4.3 (#2, Oct 6 2006, 07:52:30) [GCC 4.0.3 (Ubuntu 4.0.3-1ubuntu5)] on linux2 Type help, copyright, credits or license for more information. class Foo(): File stdin, line 1 class Foo(): ^ SyntaxError: invalid syntax class Foo( object ): ... self.x = 5 ... Traceback (most recent call last): File stdin, line 1, in ? File stdin, line 2, in Foo NameError: name 'self' is not defined -- To email me, substitute nowhere-spamcop, invalid-net. -- http://mail.python.org/mailman/listinfo/python-list
Re: Do I need self and other?
Kurda Yon wrote: Hi, I found one example which defines the addition of two vectors as a method of a class. It looks like that: class Vector: def __add__(self, other): data = [] for j in range(len(self.data)): data.append(self.data[j] + other.data[j]) return Vector(data) In this example one uses self and other. Does one really need to use this words? And, if yes, why? I have replaced self by x and other by y and everything looks OK. Is it really OK or I can have some problem in some cases? Thank you! -- http://mail.python.org/mailman/listinfo/python-list The first param self in an instance method is a convention, I would recommend not changing it. The self param is pass automatically when you call the method, like so : self.method(param) and this would have been defines as : def method(self, param): # do something here Self is like this in java, except it is explicitly added to the parameter list as the first parameter. You could name it whatever you want, but python programmers will throw tomatoes at you for naming it something else :-), since it mean myself in if the instance's perspective. Sometimes you have to pass it explicitly, like when calling your parent's method, be you'll see this when you study inheritance. I hope that helps, the self param had mixed me up some the first time I had seen it. Gabriel -- http://mail.python.org/mailman/listinfo/python-list
Re: Do I need self and other?
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Hash: SHA1
Peter Pearson wrote:
On Fri, 27 Jun 2008 20:19:00 -0400, Nick Dumas [EMAIL PROTECTED] wrote:
[snip]
Example:
class Foo():
self.x = 5
Have you tried what you're posting?
Python 2.4.3 (#2, Oct 6 2006, 07:52:30)
[GCC 4.0.3 (Ubuntu 4.0.3-1ubuntu5)] on linux2
Type help, copyright, credits or license for more information.
class Foo():
File stdin, line 1
class Foo():
^
SyntaxError: invalid syntax
class Foo( object ):
self.x = 5
Traceback (most recent call last):
File stdin, line 1, in ?
File stdin, line 2, in Foo
NameError: name 'self' is not defined
Yeah, looking back at that...bleh. Not a smart typo. But I did run the
- -proper- code, and I learned a little bit about Python and classes.
Sorry for the typo, folks.
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Re: Do I need self and other?
Kurda Yon wrote: Hi, I found one example which defines the addition of two vectors as a method of a class. It looks like that: class Vector: def __add__(self, other): data = [] for j in range(len(self.data)): data.append(self.data[j] + other.data[j]) return Vector(data) In this example one uses self and other. Does one really need to use this words? And, if yes, why? I have replaced self by x and other by y and everything looks OK. Is it really OK or I can have some problem in some cases? You can use whichever (valid) names you want, but in general 'self' and 'other' are used for clarity. In this case, they indicate the vector that is operated on (self) and another vector (other). Using 'x' and 'y' would be less clear here. -- Hans Nowak (zephyrfalcon at gmail dot com) http://4.flowsnake.org/ -- http://mail.python.org/mailman/listinfo/python-list
Re: Do I need self and other?
On Jun 27, 6:32 pm, Hans Nowak [EMAIL PROTECTED] wrote: Kurda Yon wrote: Hi, I found one example which defines the addition of two vectors as a method of a class. It looks like that: class Vector: def __add__(self, other): data = [] for j in range(len(self.data)): data.append(self.data[j] + other.data[j]) return Vector(data) In this example one uses self and other. Does one really need to use this words? And, if yes, why? I have replaced self by x and other by y and everything looks OK. Is it really OK or I can have some problem in some cases? You can use whichever (valid) names you want, but in general 'self' and 'other' are used for clarity. In this case, they indicate the vector that is operated on (self) and another vector (other). Using 'x' and 'y' would be less clear here. -- Hans Nowak (zephyrfalcon at gmail dot com)http://4.flowsnake.org/ OK, I see. In the given example self is just a name which can be replace by whichever (valid) name. Is that always like that? I mean, does slef have a special meaning in some cases or it is always just a name like any other? I am asking that because self is highlighted in my text editor, so I assume that it can have a special meaning. I also heard that self refers to a object and I am not sure what that refers means. -- http://mail.python.org/mailman/listinfo/python-list
Re: Do I need self and other?
Kurda Yon wrote: OK, I see. In the given example self is just a name which can be replace by whichever (valid) name. Is that always like that? I mean, does slef have a special meaning in some cases or it is always just a name like any other? Yes. A method is a function bound to a class or instance thereof. Def statements create functions. Parameter names are arbitrary, as long as they do not conflict with any global names you want to access from within the function. Self (and other) are simply community conventions. They do have they advantage that if they are only used as function/method parameter names, then they will not conflict with any module globals. tjr -- http://mail.python.org/mailman/listinfo/python-list
Re: Do I need self and other?
Terry Reedy wrote: Kurda Yon wrote: OK, I see. In the given example self is just a name which can be replace by whichever (valid) name. Is that always like that? I mean, does slef have a special meaning in some cases or it is always just a name like any other? Yes. A method is a function bound to a class or instance thereof. Def statements create functions. Parameter names are arbitrary, as long as they do not conflict with any global names you want to access from within the function. Self (and other) are simply community conventions. They do have they advantage that if they are only used as function/method parameter names, then they will not conflict with any module globals. It's worth noting that 'self' for the first parameter of a method is an extremely strong convention. I highly encourage you to follow it. In particular, classmethods and staticmethods don't take an instance of the class as the first argument, so using 'self' for instance methods, 'cls' for classmethods, and nothing in particular for staticmethods (since the first argument isn't special at all), helps distinguish them when reading. You risk annoying your reader by using something other than 'self' in an instance method. By contrast, using 'other' for the other argument to a binary __mathoperation__ method is not a particularly strong convention. No one will be annoyed if you use something else. -- Robert Kern I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth. -- Umberto Eco -- http://mail.python.org/mailman/listinfo/python-list
Re: Do I need self and other?
On Friday 27 June 2008 06:41:22 pm Kurda Yon wrote: OK, I see. In the given example self is just a name which can be replace by whichever (valid) name. Is that always like that? I mean, does slef have a special meaning in some cases or it is always just a name like any other? I am asking that because self is highlighted in my text editor, so I assume that it can have a special meaning. I also heard that self refers to a object and I am not sure what that refers means. It's a name, like any other. It only has special meaning on the minds of most python programmers. That name is used, by convention (and only because of convention) to refer the the ... erm... 'self' object. That said, of all python conventions, it is perhaps the one most zealously followed. That's why your editor highlights it. So, code will not break if you use any other valid name instead of self. But you shouldn't. Everything will work perfectly - except the readability. Cheers, -- Luis Zarrabeitia (aka Kyrie) Fac. de Matemática y Computación, UH. http://profesores.matcom.uh.cu/~kyrie -- http://mail.python.org/mailman/listinfo/python-list
Re: Do I need self and other?
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 Kurda Yon wrote: Hi, I found one example which defines the addition of two vectors as a method of a class. It looks like that: class Vector: def __add__(self, other): data = [] for j in range(len(self.data)): data.append(self.data[j] + other.data[j]) return Vector(data) In this example one uses self and other. Does one really need to use this words? And, if yes, why? I have replaced self by x and other by y and everything looks OK. Is it really OK or I can have some problem in some cases? Thank you! In Python, when defining the methods of a class, you pass self as an argument to these methods so that they can have access to the class's variables and methods. Example: class Foo(): self.x = 5 def bar(self): print self.x def baz(): print self.x #This raises an error. -BEGIN PGP SIGNATURE- Version: GnuPG v1.4.9 (MingW32) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iEYEARECAAYFAkhlg3QACgkQLMI5fndAv9gQZgCfRV15fQwGb9+n7Lz6JYmfXdeZ 0fYAn0fK90XfR7in/B9TjflwBRFcsgSS =qyXG -END PGP SIGNATURE- -- http://mail.python.org/mailman/listinfo/python-list
Re: Do I need self and other?
In article [EMAIL PROTECTED], Kurda Yon [EMAIL PROTECTED] wrote: Hi, I found one example which defines the addition of two vectors as a method of a class. It looks like that: class Vector: def __add__(self, other): data = [] for j in range(len(self.data)): data.append(self.data[j] + other.data[j]) return Vector(data) In this example one uses self and other. Does one really need to use this words? And, if yes, why? I have replaced self by x and other by y and everything looks OK. Is it really OK or I can have some problem in some cases? Technically, Python doesn't care what you call them. You could write: def __add__(luxury_yacht, throat_warbler_mangrove): etc, etc, etc and it would run exactly the same. That being said, don't do that. The use of self and other are pretty much de rigueur. Experienced Python programers will instantly understand what they mean. If you use anything else, they will have to spend more time trying to understand your code. -- http://mail.python.org/mailman/listinfo/python-list
Re: Do I need self and other?
In article [EMAIL PROTECTED], Kurda Yon [EMAIL PROTECTED] wrote: OK, I see. In the given example self is just a name which can be replace by whichever (valid) name. Is that always like that? I mean, does [self] have a special meaning in some cases or it is always just a name like any other? It has absolutely no special meaning. Use of the name self is pure convention. I am asking that because self is highlighted in my text editor, so I assume that it can have a special meaning. I use emacs, and the Python mode in emacs highlights it too, as if it were a keyword. But, that's just an external tool, which is free to do whatever it wants. -- http://mail.python.org/mailman/listinfo/python-list
Re: Do I need self and other?
Le Saturday 28 June 2008 00:17:33 Kurda Yon, vous avez écrit : class Vector: def __add__(self, other): data = [] for j in range(len(self.data)): data.append(self.data[j] + other.data[j]) return Vector(data) In this example one uses self and other. Does one really need to use this words? Yes, he does, because one really need to follow the conventions of a language, which belong to the language even they don't belong to its syntax. You should have a look to the PEP 8 : http://www.python.org/dev/peps/pep-0008/ self is the good name for the implicit argument of instancemethod. other is the name widely used for rvalue in binary operators definition. As for convention, your constructor, Vector(iterable), is expected to be a copy constructor, that means the Vector's __init__ method is somewhat like this : def __init__(self, iterable=()) : self.data=list(iterable) # create a copy of the parmeter First, self.data should be renamed to self._data, see PEP 8 for details, because data will probably not be part of the API of your object. Then, this make your code a bit curious, you create a list to add the two vectors, then copy it to create the resultiing vector, consuming two times the memory needed. Finally, you would probably gain in inheriting directly from the builtin type list. Here is my proposal for your Vector class (wth some other enhancements) : class Vector(list) : def __init__(self, iterable=()) : def __init__(self, iterable=()) : list.__init__(self, iterable) def __repr__(self) : return 'Vector(%s)' % list.__repr__(self) def __add__(self, other) : res = Vector() for i, elt in enumerate(self) : res.append(elt + other[i]) return res Note that I don't know how you want to deal vectors of different dimensions, you should probably raise a ValueError. Also use enumerate, i in xrange(len(iterable)) was required before enumerate was done a builtin but is rather ugly. Finally, to come to a more functionnal style the method could have been written like this : from itertools import izip ... def __add__(self, other) : return Vector(x + y for x, y in izip(self, other)) -- _ Maric Michaud -- http://mail.python.org/mailman/listinfo/python-list
