Re: Promoting Python
Op 07-04-16 om 00:03 schreef Marko Rauhamaa:
Once you look up an object method, it doesn't have a self argument. The
self argument is cooked up for the benefit of the function definition in
the class.
IOW, if I have this class:
class A:
def f(self):
print("f")
and this object:
a = A()
then,
a.f
is a function that doesn't have a self argument. That function is
generated on the fly, and it delegates to A.f, providing it with self
argument.
a.f is not a function, A.f is a function.
a.f is an instance method. The function is not generated on the fly,
when the method is called, it calls the function A.f with an extra
argument __self__ (the instance a) inserted before the argument list the
instance method was called with.
So calling a.f() is a convenient way to write A.f(a)
However, a.f itself is just a function that doesn't accept any
arguments.
As i wrote, a.f is an instance method not a function. It accepts any
argument you trow at it, insert 'a' in front of the argument list and
calls the function A.f with this new argument list.
Defining:
def f():
print("f")
a.f = f
simply short-circuits the attribute lookup process; no need to consult
the class when the attribute (method!) is right there in the object's
dict.
Here a.f is a function so Python will treat is as a function. When you
call it, the lookup process will find f in the class instance
dictionary, discover it's a function and run it with the arguments
provided. If you would like to use attributes of the class A or of the
instance 'a' in f, you would need to hard code it in the function since
the function f does not know it was called from 'a', an instance of the
class A.
Marko
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Re: deque is not a subclass of Sequence.
On 2016-04-07 11:12, Peter Otten wrote:
Antoon Pardon wrote:
Second tryal, I hope the formatting doesn't get messed up now
Playing around with the collections and collections.abc modules in
python3.4 I stumbled upon the following:
from collections.abc import Sequence
from collections import deque
isinstance(list(), Sequence)
True
isinstance(deque(), Sequence)
False
This seems strange to me. As far as I understand, the
documentation indicates there is no reason why deque
shouldn't be a subclass of Sequence.
Am I missing something or can this be considered a bug?
from collections import deque
from collections.abc import Sequence
[name for name in set(dir(Sequence)) - set(dir(deque)) if not
name.startswith("_")]
['index']
So the index() method seems to be what is missing.
The index method was added to the deque object in Python 3.5.
Python 3.5.1 (default, ...)
[GCC ...] on linux
>>> import collections
>>> isinstance(collections.deque(), collections.abc.Sequence)
True
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Re: what does 'a=b=c=[]' do
alex23 schreef op wo 21-12-2011 om 16:50 [-0800]:
> On Dec 22, 8:25 am, Eric wrote:
> > This surprises me, can someone tell me why it shouldn't? I figure if
> > I want to create and initialize three scalars the just do "a=b=c=7",
> > for example, so why not extend it to arrays.
>
> The thing to remember is that everything is an object, and that it's
> better to think of variables as labels on an object.
>
> So: a=b=c=7 means that _one_ integer object with the value of 7 can be
> referenced using any of the labels a, b or c. x=y=z=[] means that
> _one_ empty list can be referenced using x, y or z.
>
> The difference is that the value of a number object _cannot be
> changed_ ('immutable') while a list can be modified to add or remove
> items ('mutable'). a=10 just reassigns the label a to an integer
> object of value 10. x.append("foo") _modifies_ the list referred to by
> x, which is the same list known as y & z.
>
> > Also, is there a more pythonic way to do "x=[], y=[], z=[]"?
>
> I'd say that _is_ the most pythonic way, it's very obvious in its
> intent (or would be with appropriate names). If it bothers you that
> much:
>
> def listgen(count, default=[]):
> for _ in xrange(count):
> yield default[:]
>
> x, y, z = listgen(3)
>
I'm afraid it's dangerous to encourage the use of '[]' as assignment to
a parameter in a function definition. If you use the function several
times 'default' always points to the same list.
>>> def return_list(list_ = []):
>>> return list_
>>> a_list = return_list()
>>> a_list
[]
>>> a_list.append(3)
>>> a_list
[3]
>>> b_list = return_list()
>>> b_list
>>> [3] # !!??
>>> def return_list():
>>> return []
>>> a_list = return_list()
>>> a_list
[]
>>> a_list.append(3)
>>> a_list
[3]
>>> b_list = return_list()
>>> b_list
>>> []# OK!
I only use python3 so I don't know how these things work in other
versions.
No problem in your function since you yield a copy, but I've already
seen long threads about this.
I would change your function to (Python3.x):
def empty_lists(count):
for _ in range(count):
yield []
Regards,
Rolf
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plotting in python 3
Hi, What's the easiest way to plot graphs in python 3.x? Ís there a package? Quality doesn't really matter. Thanks, Rolf signature.asc Description: Dit berichtdeel is digitaal ondertekend -- http://mail.python.org/mailman/listinfo/python-list
Re: plotting in python 3
Op dinsdag 06-04-2010 om 14:55 uur [tijdzone -0500], schreef Christopher Choi: > On Tue, 06 Apr 2010 21:23:34 +0200, Rolf Camps wrote: > > > Hi, > > > > What's the easiest way to plot graphs in python 3.x? Ís there a package? > > Quality doesn't really matter. > > > > Thanks, > > > > Rolf > > Hi, > > > > What's the easiest way to plot graphs in python 3.x? Ís there a package? > > Quality doesn't really matter. > > > > Thanks, > > > > Rolf > > I would like to think you have done some home work yourself > but anyways... gnuplot with python seems easy. > . > > http://gnuplot-py.sourceforge.net/doc/ It was after the homework I asked my question. All plot solutions i found where for python2.x. gnuplot_py states on its homepage you need a 'working copy of numpy'. I don't think numpy is ported to python 3.x. Or is it? > > Chris signature.asc Description: Dit berichtdeel is digitaal ondertekend -- http://mail.python.org/mailman/listinfo/python-list
