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00:00:02
Sergey Balakirev and in this lesson we
00:00:04
will learn how to create objects in python and define
00:00:06
classes, that is,
00:00:09
instances of these classes, and also
00:00:11
add and delete their attributes, that is,
00:00:13
data. Suppose we want to define a
00:00:16
class for storing the coordinates of points on a
00:00:18
plane for I’ll start by writing it down without
00:00:21
any content, for this we
00:00:24
first write the following keyword class
00:00:26
and then, separated by a space, we define the name of
00:00:29
this class, but let it be called like this
00:00:32
point, but then here we have
00:00:34
the contents of the class, that is, we put: and
00:00:38
y we begin with a block for the class, that is,
00:00:41
everything that we define here inside us
00:00:43
will relate to this class point,
00:00:45
let it be empty for now, I
00:00:48
will put such an operator pass, we all have
00:00:51
defined a class named point and
00:00:54
look in accordance with the
00:00:57
IEC 8 standard name It is customary to start a class with a
00:01:00
capital letter and, of course, name it
00:01:03
so that it reflects the essence of this class.
00:01:06
In the future, I will adhere to this
00:01:08
rule and so we have the
00:01:10
simplest definition of a class, but in this
00:01:13
form it is not particularly useful, so I
00:01:16
will write two attributes in it 1 attribute
00:01:19
let him call the rock, that is, the color and
00:01:21
taking this value ed and the second
00:01:24
requires glasses that will determine
00:01:26
the radius. Well, let it be equal to two. Pay
00:01:30
attention to the variable inside the class, they are usually
00:01:33
called attributes of the class or its
00:01:37
properties. I will
00:01:39
use this terminology in the future.
00:01:40
Now in our class there are two of these
00:01:43
attributes of the glasses, but how to
00:01:46
correctly perceive this construction;
00:01:49
in fact, the class itself forms a
00:01:52
namespace in this case with
00:01:54
the name point and in this namespace
00:01:58
there are two variables cola and secl and
00:02:01
we can access them using
00:02:04
the syntax for the namespace, for example, this is how
00:02:07
I copy this class, go to the
00:02:09
python console and the correspondence is created,
00:02:12
this class is right here
00:02:13
directly in the python console, this is how it
00:02:15
will be It’s more convenient to show here on
00:02:17
the right here we have this class, here
00:02:20
it is point and, accordingly, it contains two of
00:02:22
these from the variable, that is, two
00:02:24
properties of glass and color and now
00:02:27
look, we can write the name of this
00:02:30
class a point, that is, the namespace
00:02:33
point, put a dot and here we
00:02:36
have two of our properties color and sekl, but
00:02:40
let me select color and assign it
00:02:42
some other value, for example,
00:02:44
black even enter and look here on the
00:02:47
right we have this color property
00:02:49
changed from red to black, or
00:02:52
we can read what -a property
00:02:55
from this class, that is, write down
00:02:57
its name again, put a dot, and define,
00:03:01
select some property here, let
00:03:03
the glass, press enter and we have it spinning
00:03:06
the value 2, which is exactly contained in
00:03:09
this property, and to see all
00:03:11
the attributes of the class, you can use
00:03:13
this a special variable
00:03:16
called dict, that is, two
00:03:18
underscores dict and 2 underscores
00:03:21
by pressing enter and we have such a
00:03:23
collection reminiscent of a dictionary and here
00:03:26
we have many, many different attributes and among
00:03:29
them there are two of ours, this is this color with the
00:03:32
value black and falcon with the value 2
00:03:35
Now let's take the next step and
00:03:38
create instances of this class. About our
00:03:42
case, to create an object, that is, an
00:03:44
instance of a class is enough
00:03:47
to put two
00:03:50
parentheses like this after its name, press enter and look on
00:03:53
the right we have this change and
00:03:55
which is just an instance of
00:03:59
this class point and through this
00:04:01
variable there are two such
00:04:03
attributes available, two properties color and circle
00:04:06
that are defined in this
00:04:08
point class, or we can create another
00:04:10
instance using exactly the same
00:04:13
syntax, but example b equals point and
00:04:16
two parentheses, press enter and
00:04:19
we have the second variable b which has a
00:04:22
completely different address, here we are in this
00:04:24
video, this means the address of variable b
00:04:26
and the address of variable a are different, this
00:04:30
means that object a and object b are
00:04:34
completely two times independent objects
00:04:37
and object b also contains these two
00:04:40
properties of glass and color by analogy,
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it can create an arbitrary number of
00:04:45
instances of a class, since variables a
00:04:48
and b refer to objects of the class
00:04:51
point, we can clearly determine this
00:04:54
using such a function type, I write
00:04:56
type and ad, and then at the output we will see that this is nothing more than an
00:05:00
object is a class point,
00:05:02
that is, it belongs to a type of
00:05:04
this class point, and we can even
00:05:07
check it explicitly like this if we write type
00:05:09
from a-two equals and point at the output we get
00:05:13
a container or in this form from
00:05:16
instance a, point in in this case, we
00:05:20
will also get true as an output, that is, the name of the
00:05:23
classes here acts as a
00:05:25
data type, but let’s take a closer look at
00:05:28
what we have here and in
00:05:30
reality what happened is, firstly,
00:05:33
objects a and b form their own namespace, the
00:05:36
namespace of
00:05:39
class instances and, secondly, secondly, it does not contain any
00:05:43
of its own attributes, the color and
00:05:47
circle properties are taken directly from the
00:05:50
point class inside these objects a and b,
00:05:53
these properties do not exist, they do not exist, they
00:05:57
refer to the corresponding properties
00:05:59
attributes of this class point,
00:06:02
so it is not by chance that I call these two
00:06:05
variables
00:06:06
attributes of the class highlights the fact
00:06:09
that these changes are inside the
00:06:13
point class, that is, the attributes of the class are common
00:06:17
to all its instances and we can
00:06:21
easily verify this,
00:06:22
for example, let's change this
00:06:24
property of glass, it now
00:06:26
takes the value 2 and we will set the
00:06:29
value to 1, I press enter and look
00:06:32
here, then automatically in our
00:06:34
objects this value also changed from
00:06:36
two to one, and whether
00:06:40
you look at it or not, but this collection of dict from
00:06:42
this object, and for example, it will be
00:06:45
empty, this just means that the
00:06:47
object itself and now is not contains
00:06:51
no attributes and the same with
00:06:54
object b, it will also be empty, that is,
00:06:56
this dict collection will be empty, that is,
00:06:59
our objects a and b form spaces,
00:07:02
but in this namespace there is
00:07:05
nothing yet, but nevertheless we
00:07:08
can access attributes through them class
00:07:11
point that is, write a. for example,
00:07:15
color then we will see this value black,
00:07:17
that is, this value of the goods was taken
00:07:20
directly from the point class, or
00:07:22
we can write it like this.
00:07:24
respectively, we get the value 1, but
00:07:27
if we execute the following command a .
00:07:30
color and assign some other color,
00:07:32
for example green, then look what we
00:07:34
get, I press enter and on the right
00:07:38
here, object a of the color properties
00:07:41
takes Gorin and object b of the
00:07:44
color properties remains good, why did this happen, the
00:07:48
thing is that when we do
00:07:51
this command then through a
00:07:54
we access this namespace
00:07:57
to the namespace of the object a and then
00:08:00
this assignment operator
00:08:03
creates a variable named color in the
00:08:07
current namespace despite the fact
00:08:11
that we can take this
00:08:12
variable from another namespace
00:08:15
from an external space from the point class,
00:08:17
but this assignment operator
00:08:20
works like this: if the variable
00:08:23
color is not present in this current
00:08:26
namespace, then it is a variable, that
00:08:29
is, in this case, the attribute is created in
00:08:32
this current namespace and as a result,
00:08:36
object a already contains its own
00:08:39
attribute, then properties with this name
00:08:42
color, but object b still
00:08:45
refers to the color of this
00:08:48
point class, and we can also verify this
00:08:50
if we print the collection for this
00:08:54
object a, that is, we write a.a. dict and
00:08:58
look here we have these
00:09:00
local properties with the name color and the
00:09:03
value green, this is a point you need to
00:09:06
know and understand very well. On
00:09:09
this principle in python the
00:09:11
formation of class attributes and
00:09:14
local attributes of their instances is built. By
00:09:16
the way, by analogy we can create
00:09:19
new attributes and in the point class, to do
00:09:22
this, just write down the name of the class,
00:09:24
put a dot, but also come up with
00:09:27
some new property for us product
00:09:29
type pt and assign some
00:09:33
value to let the value be disk,
00:09:35
press enter and look, we have
00:09:38
these new objects here
00:09:40
properties type t with the value disk
00:09:43
and if we look at the point to class, in
00:09:46
this point class these
00:09:49
new properties have also appeared, that is, like this
00:09:51
we can dynamically add new
00:09:55
properties to this class, that is, a new
00:09:57
attribute or the same thing we can
00:09:59
do it using a special
00:10:01
function called set and tatar,
00:10:04
as the first argument we indicate
00:10:06
the namespace with which we want to
00:10:09
work, let it be the point class, and
00:10:11
then through the beaten second argument in the
00:10:14
form of a string, pay attention to the form of a
00:10:16
string, we must register that property
00:10:19
someone an attribute to which we want to assign
00:10:22
this or that value,
00:10:23
here I have written a completely new
00:10:25
probe attribute which is not yet in the
00:10:28
point class and let it take it, it
00:10:31
requires the value 1, that is, here are three such
00:10:34
arguments by pressing enter and look,
00:10:37
this attribute has appeared in the point class a
00:10:40
property of samples with a value of 1, that is,
00:10:43
if there is no attribute in the class to
00:10:47
which we want to assign a
00:10:49
value, then it is dynamically added to it,
00:10:52
and if we write here
00:10:55
some already existing
00:10:57
euro attribute like type t and assign new
00:10:59
values ​​to press quar then Let’s just
00:11:02
change the value of disk, which is here,
00:11:05
to the new values ​​of square, that is, this is how
00:11:08
we can work with class attributes,
00:11:11
dynamically adding them and changing
00:11:14
the value; if we want to read
00:11:16
any attribute value from a class,
00:11:19
then for this we just need to write the
00:11:21
class name or name again instance of a class, it doesn’t
00:11:24
matter, well, and accordingly indicate
00:11:27
the attribute that we want to access,
00:11:30
for example, glass at the output will get
00:11:32
this value 1, but or we can assign the
00:11:35
result of this attribute to some variable
00:11:37
and the corresponding variable
00:11:39
will contain the
00:11:40
value of this attribute, but when accessing a
00:11:45
non-existent class attribute, for example
00:11:47
but it doesn’t exist, we’ll get an error.
00:11:50
This error can be avoided if
00:11:54
we use a special function
00:11:56
called get to the top, it
00:11:59
allows you to read an attribute from the
00:12:01
specified namespace. In this
00:12:04
case, I specify a class, but you can also specify
00:12:06
objects of the class, it doesn’t matter, I specify
00:12:09
the class and given, separated by a comma, I will indicate a
00:12:12
non-existent attribute, and if we
00:12:15
write it like this, we will again get an error, but
00:12:19
here you can also enter a third argument, I will enter it like this:
00:12:22
fall and this third
00:12:25
argument will be returned if the
00:12:28
specified attribute is not detected, but what
00:12:31
if we indicate existing
00:12:34
properties here, for example color then it
00:12:36
corresponds to the return and you can
00:12:39
write off this goto top function in this form,
00:12:41
or you can
00:12:43
not write this third argument; in this case,
00:12:46
green will also be the result, but if this
00:12:48
color attribute is not in the point
00:12:51
to class with a plumb line, we will get an error
00:12:53
finally, we can not only add but
00:12:56
also remove any attributes from the class, and
00:12:58
this can be done in at least two
00:13:00
ways, the first is to use the article
00:13:03
about the dl operator, but also
00:13:05
indicate which attribute from which
00:13:07
namespace is being removed, in this
00:13:09
case we want to remove from the point class
00:13:12
here Let’s say this is the sample attribute by pressing
00:13:15
enter and look in our point class,
00:13:18
now this sample attribute is not there, we
00:13:21
have deleted it, but if we try to repeat
00:13:23
this command, we will already have an error
00:13:26
because we cannot delete a non-existent
00:13:29
kite sport attribute, the del command is impossible,
00:13:31
so before we emphasize this
00:13:34
or of another attribute, in theory, it would be
00:13:36
good to check whether it exists or
00:13:39
not, for this you can call
00:13:42
this special function called so
00:13:44
tomorrow, and accordingly, here
00:13:46
we indicate the namespace, that is, in
00:13:49
this case, I will indicate the class, and the
00:13:51
property that we are going to remove
00:13:53
samples for in the output it will give a fall because
00:13:59
there is no such property of such an attribute in the class, if it were there we will see
00:14:02
either the value true, but let me write it
00:14:04
here and press enter and we
00:14:07
have the value true because
00:14:09
such a property exists in the point class,
00:14:11
so here’s the first one the way to delete an attribute
00:14:14
is the dl operator and the second way is
00:14:17
to use a function called
00:14:19
del a tatar, here we indicate with the first
00:14:22
argument the namespace from which the
00:14:24
attribute is deleted, well, given this attribute
00:14:27
that we are going to delete, for
00:14:29
example, this is type pt, press
00:14:32
enter and look at
00:14:34
This attribute, etc., was indeed removed from our classes.
00:14:36
Of course, if we call the
00:14:40
same function again for the same
00:14:42
attribute, we will get an error, that is,
00:14:45
only those attributes that
00:14:47
are present in the class can be deleted, so before
00:14:50
deleting anything, we need to check whether
00:14:52
such an attribute exists in the class or not,
00:14:55
and the same thing with objects, whether
00:14:57
such an attribute exists in the object or does
00:15:00
not exist, and look, if we
00:15:02
now call this
00:15:04
swizer function for the point class and specify an attribute
00:15:08
that exists, let’s say color, then of
00:15:11
course we will get the value true, and if
00:15:13
we specify the name of the object here, for example, we
00:15:16
also see true yes, I forgot that we
00:15:19
created this color property
00:15:21
directly in this instance,
00:15:23
so of course we see a corpse here,
00:15:25
let’s write glass instead of color,
00:15:27
press enter, we see the same trope, that is,
00:15:30
this function and but it says
00:15:33
that we can, in principle, get
00:15:35
through the namespace and access from to
00:15:38
this attribute is called, but it does not say
00:15:41
that this attribute is located
00:15:44
directly from in this
00:15:47
namespace, but pay attention to this, that
00:15:50
is, if we are here, we see a
00:15:51
collection of dictates, look,
00:15:54
there is only one attribute in it and these are the
00:15:57
2 attributes of the falcon, there are no here,
00:16:00
however, the gas function from r returns
00:16:03
the value true that we, in principle,
00:16:05
through and we can access this
00:16:07
attribute of glass, that is, the functions is at
00:16:09
our work and this is exactly the way, but the
00:16:12
removal of attributes occurs
00:16:14
directly in the current space of the
00:16:16
honey fraer, if we write for and here
00:16:19
we indicate glass, that is, this is the
00:16:21
glass attribute, it is missing in the secant
00:16:24
namespace, then we will get an error,
00:16:26
but we can completely remove color
00:16:30
because it is present in this object,
00:16:32
execute this line pay attention
00:16:35
in our object and this color property
00:16:38
takes the value garena now we
00:16:41
will remove this property from the object and I
00:16:44
press enter and we get the following
00:16:47
in this object and this color property
00:16:50
remains but already takes the value black
00:16:54
I think you guessed why this
00:16:57
happened in then after removing the
00:16:59
color attribute from the object, and this color
00:17:02
became a brother directly from the
00:17:05
point class, that is, the search for one or another
00:17:08
attribute is performed as follows:
00:17:10
first, it is searched in the current space
00:17:13
honey, and if it is not here, then it is taken
00:17:17
from the next external one, which
00:17:20
corresponds to this one. here is the
00:17:22
internal space in this case, the
00:17:24
external space for any object is the class from
00:17:27
which it was formed, but in this
00:17:30
case from the point class, so this
00:17:32
color attribute for object a is taken
00:17:35
from the point class, this point
00:17:38
should also be well understood when working with
00:17:40
local properties objects and
00:17:42
class attributes, and so now that we
00:17:45
have figured out how attributes are created,
00:17:48
let’s return to our task of creating
00:17:50
point objects on the plane. I will again
00:17:53
define this point class again and
00:17:56
also re-create two objects object a
00:17:59
and object b. For these two objects we
00:18:03
automatically get these are two
00:18:05
common properties of glass and color, but
00:18:08
the coordinates of the points of these objects must
00:18:11
exclusively belong to this
00:18:14
instance, so we will write these coordinates
00:18:17
as follows, we will indicate the
00:18:19
namespaces, that is, of the object, and we
00:18:22
will put a point, I will write the first
00:18:24
coordinate as x and assign the value 1
00:18:27
accordingly you are here about so in object
00:18:30
and we have a new local
00:18:33
property with the name x and
00:18:36
value 1, and the same for the second
00:18:39
coordinate y, I’ll just write the value 2
00:18:42
as a result, object a contains two of its
00:18:46
own local properties x and y with
00:18:49
values ​​1 and 2 and that is, the coordinate of
00:18:52
the point, well, we can
00:18:54
write the same thing for object b, let there
00:18:57
be coordinates 10 and 20, that is, these are the
00:19:00
x y property that we defined in
00:19:02
this way, that is, we
00:19:04
dynamically created them for the
00:19:07
corresponding instances of the class, they
00:19:10
are independent between As a
00:19:13
result, each object
00:19:15
represents a point with independent
00:19:18
coordinates on the plane, but the colors and their
00:19:22
size are like common data for
00:19:25
all these objects, that is, in this
00:19:27
way we can create a local
00:19:30
individual property for each
00:19:32
object, and at the end of this lesson,
00:19:35
I’ll note that in any class of the python language
00:19:38
we can define its description in the form of
00:19:41
this starting line, if we
00:19:43
now define in the console just
00:19:46
such a class with this 1 line,
00:19:48
look, this class has
00:19:51
this change, it’s called dogs 2
00:19:53
underscores long 2 underline and
00:19:56
this variable doc just contains
00:19:59
that line, the description that we
00:20:01
write here at the beginning usually
00:20:03
does this when creating large programs
00:20:05
when they create such descriptions in key classes
00:20:08
so that in the
00:20:10
future it would be more convenient to return to
00:20:13
them, correct them and use them without
00:20:15
referring to special documentation and
00:20:17
so from this lesson you should have a good
00:20:19
idea of ​​how python classes are defined
00:20:21
and how class objects are created,
00:20:24
what a class attribute and an
00:20:27
object attribute represent themselves be able to access this
00:20:31
attribute using attacks from the function
00:20:34
adding read check for the presence
00:20:37
and removal of attributes and also know
00:20:40
what are these two changes responsible for?
00:20:42
If all this is clear to you, then feel free
00:20:44
to move on to the next lesson
00:20:46
[music]

Description:

Курс по Python ООП: https://stepik.org/course/116336/promo Узнаете, что такое класс и как создавать экземпляры классов. Функции type и isinstance для объектов класса. Создание атрибутов классов и объектов. Функции: getattr(), hasattr(), setattr(), delattr(). Свойства: __doc__ и __dict__. Инфо-сайт: https://proproprogs.ru/python_oop Telegram-канал: https://t.me/python_selfedu

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