17 OOP 4: Data Class, Iterators, Generators, Context Managers

Դադիվանք, լուսանկարի հղումը, Հեղինակ՝ Naré Gevorgyan

📚 Նյութը

Dataclasses

class Person:
    def __init__(self, first_name, last_name, id_number=None):
        self.first_name = first_name
        self.last_name = last_name
        self.id_number = id_number
        
p = Person("John", "Smith", "509")

print(p)

<__main__.Person object at 0x0000023A18696710>

class Person:
    def __init__(self, first_name, last_name, id_number=None):
        self.first_name = first_name
        self.last_name = last_name
        self.id_number = id_number
        
    def __repr__(self):
        return f"Person({self.first_name}, {self.last_name}, {self.id_number})"
    
p = Person("John", "Smith", "509")

print(p)

Person(John, Smith, 509)

from dataclasses import dataclass

@dataclass
class Person:
    first_name: str # type hint
    last_name: str
    id_number: str

p = Person("John", "Smith", "509")

Person(first_name='John', last_name='Smith', id_number='509')

Here, __init__, __repr__, and __eq__ come for free.

from dataclasses import dataclass

@dataclass
class Person:
    first_name: str    # becomes a field
    last_name          # no annotation → ignored by dataclasses
    id_number: str     # becomes a field

p = Person("John", "Smith", "509")

---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
Input In [54], in <cell line: 3>()
      1 from dataclasses import dataclass
      3 @dataclass
----> 4 class Person:
      5     first_name: str    # becomes a field
      6     last_name          # no annotation → ignored by dataclasses

Input In [54], in Person()
      3 @dataclass
      4 class Person:
      5     first_name: str    # becomes a field
----> 6     last_name          # no annotation → ignored by dataclasses
      7     id_number: str

NameError: name 'last_name' is not defined

Default values

datetime.date(2025, 6, 20)

from dataclasses import dataclass, field
from datetime import date

@dataclass
class Person:
    first_name: str
    last_name: str
    id_number: str
    email: str = "չունի"                                # simple default
    signup_date: date = field(default_factory=date.today)  # today by default
    lst: list = field(default_factory=list)  # empty list by default
# Usage
p = Person("John", "Smith", "509")
print(p.email, p.signup_date, p.lst)

չունի 2025-06-20 []

Excluding arguments for the initializer

@dataclass
class Person:
    first_name: str
    last_name: str
    id_number: str
    secret_code: str = field(init=False)  # not passed to __init__

# Usage
p = Person("John", "Smith", "509")

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Input In [60], in <cell line: 9>()
      6     secret_code: str# = field(init=False)  # not passed to __init__
      8 # Usage
----> 9 p = Person("John", "Smith", "509")

TypeError: Person.__init__() missing 1 required positional argument: 'secret_code'

class Person:
    def __init__(self, first_name, last_name, id_number=None):
        self.first_name = first_name
        self.last_name = last_name
        self.id_number = id_number
        
        
        self.full_name = f"{self.first_name} {self.last_name}"  # computed property
        if self.name == "a":
            raise ValueError("Name cannot be 'a'")  # validation
# Usage
p = Person("John", "Smith", "509", "12321")
print(p)

Person(first_name='John', last_name='Smith', id_number='509')

`__post_init__`

@dataclass
class Person:
    first_name: str
    last_name: str
    id_number: str
    full_name: str = field(init=False)

    def __post_init__(self):
        # derive full_name from other fields
        object.__setattr__(self, 'full_name', f"{self.first_name} {self.last_name}")

# Usage
p = Person("John", "Smith", "509")
print(p.full_name)

John Smith

Freezing a data class

@dataclass(frozen=True)
class Person:
    first_name: str
    last_name: str
    id_number: str

# Usage
p = Person("John", "Smith", "509")

p.first_name = "johnny la gente esta muy loca"  # FrozenInstanceError

---------------------------------------------------------------------------
FrozenInstanceError                       Traceback (most recent call last)
Input In [69], in <cell line: 10>()
      7 # Usage
      8 p = Person("John", "Smith", "509")
---> 10 p.first_name = "johnny la gente esta muy loca"  # FrozenInstanceError

File <string>:4, in __setattr__(self, name, value)

FrozenInstanceError: cannot assign to field 'first_name'

Regular staff

@dataclass(frozen=True)
class Person:
    first_name: str
    last_name: str
    id_number: str

    def get_paniramid(self):
        for i in range(15):
            print("🧀"*i)

p = Person("John", "Smith", "509")

p.get_paniramid()


🧀
🧀🧀
🧀🧀🧀
🧀🧀🧀🧀
🧀🧀🧀🧀🧀
🧀🧀🧀🧀🧀🧀
🧀🧀🧀🧀🧀🧀🧀
🧀🧀🧀🧀🧀🧀🧀🧀
🧀🧀🧀🧀🧀🧀🧀🧀🧀
🧀🧀🧀🧀🧀🧀🧀🧀🧀🧀
🧀🧀🧀🧀🧀🧀🧀🧀🧀🧀🧀
🧀🧀🧀🧀🧀🧀🧀🧀🧀🧀🧀🧀
🧀🧀🧀🧀🧀🧀🧀🧀🧀🧀🧀🧀🧀
🧀🧀🧀🧀🧀🧀🧀🧀🧀🧀🧀🧀🧀🧀

Generators

Լավ նյութեր 1. https://realpython.com/introduction-to-python-generators/ 2. https://www.youtube.com/watch?v=bD05uGo_sVI


print(type(range(1,3)))
print(range(1,3))

<class 'range'>
range(1, 3)

a = [i**2 for i in range(-3, 3)]
print(a)
a = {i**2 for i in range(-3, 3)}
print(a)
a = (i**2 for i in range(-3, 3))
print(a)
a = tuple(i**2 for i in range(-3, 3))
print(a)

[9, 4, 1, 0, 1, 4]
{0, 9, 4, 1}
<generator object <genexpr> at 0x0000023A186F35A0>
(9, 4, 1, 0, 1, 4)

for i in [1,2,3,4,5,6,7,8,9,10]:
    print(i**2)

for i in range(1,11):
    print(i**2)

print([1,2,3,4,5,6,7,8,9,10].__sizeof__())
print(range(1,11).__sizeof__())

120
48

print([1,2,3,4,5,6,7,8,9,10,11].__sizeof__())
print(range(1, 1000000000000000000000000000000000000000).__sizeof__())


# # start = 1
# end = 10
# step = 3
# start = 4 + 3 = 7 
for i in range(1, 10, 3):
    start, stop, step

136
48

քառակուսի բարձրացնելու օրինակ

def qarakusi_bardzracnel(tver):
    qarakusiner = []
    for i in tver:
        qarakusiner.append(i**2)
    return qarakusiner

tver = list(range(-5, 5))
print(qarakusi_bardzracnel(tver))

[25, 16, 9, 4, 1, 0, 1, 4, 9, 16]

def qarakusi_bardzracnel(tver):
    for i in tver:
        yield i**2

tver = list(range(-5, 5))
print(qarakusi_bardzracnel(tver))

<generator object qarakusi_bardzracnel at 0x0000023A18715F50>

generator = qarakusi_bardzracnel(tver)

next(generator)

for i in generator:
    print(i)

next(generator) # .__next__()
next(generator)
next(generator)
next(generator)
next(generator)
next(generator)
next(generator)

---------------------------------------------------------------------------
StopIteration                             Traceback (most recent call last)
Input In [89], in <cell line: 1>()
----> 1 next(generator)
      2 next(generator)
      3 next(generator)

StopIteration:

Comprehension-ի տեսքով

qarakusiner = [i**2 for i in range(-5, 5)]
print(qarakusiner)

[25, 16, 9, 4, 1, 0, 1, 4, 9, 16]

qarakusiner = (i**2 for i in range(-5, 5))
print(qarakusiner)

<generator object <genexpr> at 0x0000023A18717C30>

next(qarakusiner)

# print(range(3,5))
# print(list(range(3,5)))

list(qarakusiner)

[16, 9, 4, 1, 0, 1, 4, 9, 16]

list(range(-5,5))

# [next(), StopIteration

[-5, -4, -3, -2, -1, 0, 1, 2, 3, 4]

Iterators, iterables

Նյութեր

https://realpython.com/python-iterators-iterables/#iterating-through-iterables-with-for-loops
https://www.programiz.com/python-programming/iterator
https://www.youtube.com/watch?v=jTYiNjvnHZY
https://www.youtube.com/watch?v=C3Z9lJXI6Qw

եկեք հիմա էլ նայենք ոնցա աշխատում for loopը

lst = [1, 2, 3]

for i in lst:
    print(i)
    
# lst[0] # lst.__getitem__(0)
# print(lst) # lst.__str__()

# {1,2,3}[0]
# lst -> for loop

1
2
3

lst = [1, 2, 3]

next(lst) # a.__next__()

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Input In [97], in <cell line: 3>()
      1 lst = [1, 2, 3]
----> 3 next(lst) # a.__next__()

TypeError: 'list' object is not an iterator

type(lst)

list

iter(lst)

<list_iterator at 0x23a186ecf70>

print(type(lst))
a_iter = iter(lst) # __iter__()
print(type(a_iter))

<class 'list'>
<class 'list_iterator'>

next(a_iter) # a_iter.__next__()

---------------------------------------------------------------------------
StopIteration                             Traceback (most recent call last)
Input In [105], in <cell line: 1>()
----> 1 next(a_iter)

StopIteration:

class VrazList:
    def __init__(self, lst):
        self.lst = lst

    def __iter__(self):
        pass

a = VrazList([1,2,3,4,5])
print(a)
print(type(a))
print(a.lst)

<__main__.VrazList object at 0x0000023A186EEB00>
<class '__main__.VrazList'>
[1, 2, 3, 4, 5]

for i in a:
    print(i)

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Input In [108], in <cell line: 1>()
----> 1 for i in a:
      2     print(i)

TypeError: iter() returned non-iterator of type 'NoneType'

class VrazList:
    def __init__(self, lst):
        self.lst = lst
        self.index = 0

    def __iter__(self):
        return self

    def __next__(self):
        current = self.lst[self.index]
        self.index += 2
        return current

for i in [1, 2, 3, 4, 5]:
    print(i)

a = VrazList([1,2,3,4,5])

# a_iter = iter(a)
# next(a_iter)
print(type(a))

for i in a:
    print(i)
    
# a -> iter(a)
# next(a)
# next(a)
# while StopIteration:

<class '__main__.VrazList'>
1
3
5

---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
Input In [110], in <cell line: 7>()
      3 # a_iter = iter(a)
      4 # next(a_iter)
      5 print(type(a))
----> 7 for i in a:
      8     print(i)

Input In [109], in VrazList.__next__(self)
      9 def __next__(self):
---> 10     current = self.lst[self.index]
     11     self.index += 2
     12     return current

IndexError: list index out of range

class VrazList:
    def __init__(self, lst):
        self.lst = lst
        self.index = 0

    def __iter__(self):
        return self

    def __next__(self):
        if self.index >= len(self.lst):
            raise StopIteration

        current = self.lst[self.index]
        self.index += 2
        return current

a = VrazList([1,2,3,4,5])

for i in a:
    print(i)

1
3
5

a = VrazList([1,2,3,4,5])

while True:
    try:
        i = next(a)
        print(i)

    except StopIteration:
        break

1
3
5

Context managers (with)

լավ նյութ՝ https://www.youtube.com/watch?v=-aKFBoZpiqA

f = open("panir.txt", "w")
f.write("պանիր պանիր պանիր")

print(f.closed)  # False

f.close()
print(f.closed)  # True

False
True

with open("panir.txt", "w") as f:
    f.write("պանիր պանիր պանիր")

# f.__exit__(None, None, None)  # f.close() is called automatically

print(f.closed)
# ոնցա՞ հասկանում որ պետքա close անի վերջում

True

Իրականում մենք ճկունություն ունենք ոչ միայն ընդգծելու թե ինչ պետք ա աշխատեի էդ f.write("պանիր պանիր պանիր")-ից հետո (էս դեպքում՝ f.close()), բայց նաև ինչ աշխատի մինչև էդ with-ի մեջ եղած կոդը

class Bacich:
    def __init__(self, name, mode):
        self.name = name
        self.mode = mode

    def __enter__(self):
        print(f"\nհեսա փորձելու ենք բացել {self.name}-ը {self.mode} նպատակով")
        self.file = open(self.name, self.mode)
        return self.file

    def __exit__(self, exc_type, exc_val, traceback):
        print("\nփակենք")
        self.file.close()

a = Bacich("panir.txt", "r")
a.__enter__()


հեսա փորձելու ենք բացել panir.txt-ը r նպատակով

<_io.TextIOWrapper name='panir.txt' mode='r' encoding='UTF-8'>

a.file

<_io.TextIOWrapper name='panir.txt' mode='r' encoding='UTF-8'>


with Bacich("panir.txt", "r") as f:
    # some code
    print(f.read())

# print(f.closed)
# # Bacich("panir.txt", "r") -> __enter__()
# enter's returns -> f

# print(f.read())

# f.__exit__(None, None, None)  # __exit__ is called automatically


# f = Bacich("panir.txt", "r").__enter__()
# # some code
# Bacich("panir.txt", "r").__exit__()


հեսա փորձելու ենք բացել panir.txt-ը r նպատակով
պանիր պանիր պանիր

փակենք

f.closed

True

աշխատեց enter-ը հետո with-ի մեջի կոդը, հետո exit-ը

# exc_type ...

class Bacich:
    def __init__(self, name, mode):
        self.name = name
        self.mode = mode

    def __enter__(self):
        print("\nհեսա փորձելու ենք բացել {self.name}ը {self.mode} նպատակով\n")
        self.file = open(self.name, self.mode)
        return self.file

    def __exit__(self, exc_type, exc_val, traceback):
        print("\nփակենք")
        print("exc_type =", exc_type) # exception type
        print("exc_val =", exc_val)
        print("traceback = ", traceback)
        self.file.close()

with Bacich("panir.txt", "r") as f:
    print("ա")
    print(f.read())

print(f.closed)


հեսա փորձելու ենք բացել {self.name}ը {self.mode} նպատակով

ա
պանիր պանիր պանիր

փակենք
exc_type = None
exc_val = None
traceback =  None
True

with Bacich("panir.txt", "r") as f:
    print("ա")
    print(lav_katakner_haykic)
    print(f.read())
    
# ...
# f.__exit__(Errort, ...., traceback)


հեսա փորձելու ենք բացել {self.name}ը {self.mode} նպատակով

ա

փակենք
exc_type = <class 'NameError'>
exc_val = name 'lav_katakner_haykic' is not defined
traceback =  <traceback object at 0x0000023A1873C180>

---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
Input In [134], in <cell line: 1>()
      1 with Bacich("panir.txt", "r") as f:
      2     print("ա")
----> 3     print(lav_katakner_haykic)
      4     print(f.read())

NameError: name 'lav_katakner_haykic' is not defined

ԻՆչ-որ հարցրեք - հլը մի րոպե բայց, բայց open-ը ֆունցկիա ա ոչ թե class, էս ո՞նց ա աշխատում

Ֆունկցիաների համար - contextmanager decorator

type(open)

builtin_function_or_method

from contextlib import contextmanager

@contextmanager
def bacich(name, mode):
    # __enter__ method
    print(f"հեսա փորձելու ենք բացել {name}ը {mode} նպատակով\n")
    file = open(name, mode)
    yield file # return
    # __exit__ method
    print("\nժամանակն է փակելու ֆայլը")
    file.close()


# class Bacich:
#     def __init__(self, name, mode):
#         self.name = name
#         self.mode = mode

#     def __enter__(self):
#         print("\nհեսա փորձելու ենք բացել {self.name}ը {self.mode} նպատակով\n")
#         self.file = open(self.name, self.mode)
#         return self.file

#     def __exit__(self, exc_type, exc_val, traceback):
#         print("\nփակենք")
#         print("exc_type =", exc_type)
#         print("exc_val =", exc_val)
#         print("traceback = ", traceback)
#         self.file.close()

with bacich("panir.txt", "r") as f:
    print("a")
    print(f.read())

print(f.closed)

հեսա փորձելու ենք բացել panir.txtը r նպատակով

a
պանիր պանիր պանիր

ժամանակն է փակելու ֆայլը
True

Աշխատումա բացիչ ֆունկցիայի բոլոր տողերը մինչև yield
yield արած արժեքը վերագրվումա fին
աշխատումա withի միջի կոդը
աշխատումա yieldից հետո գրվածը

with bacich("panir.txt", "r") as f:
    print("a")
    print(lav_katakner_haykic_2)
    print(f.read())

---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
Input In [45], in <cell line: 1>()
----> 1 with bacich("panir.txt", "r") as f:
      2     print("a")
      3     print(lav_katakner_haykic_2)

NameError: name 'bacich' is not defined

f.closed

True

from contextlib import contextmanager

@contextmanager
def bacich(name, mode):
    try:
        print(f"հեսա փորձելու ենք բացել {name}ը {mode} նպատակով\n")
        file = open(name, mode)
        yield file
    finally: # որ միշտ աշխատի
        print("\nժամանակն է փակելու ֆայլը")
        file.close()

with bacich("panir.txt", "r") as f:
    print("a")
    print(lav_katakner_haykic_2)
    print(f.read())

հեսա փորձելու ենք բացել panir.txtը r նպատակով

a

ժամանակն է փակելու ֆայլը

---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
Input In [139], in <cell line: 1>()
      1 with bacich("panir.txt", "r") as f:
      2     print("a")
----> 3     print(lav_katakner_haykic_2)
      4     print(f.read())

NameError: name 'lav_katakner_haykic_2' is not defined

print(f.closed)

True

Օրինակ - timer

import time
from contextlib import contextmanager

@contextmanager
def timer():
    start_time = time.time()
    yield
    end_time = time.time()
    print(f"Duration: {end_time - start_time} seconds")

with timer():
    print("սկսենք երգել")
    print("շուդադի շուդադա վիզաութ յոռ լավ")
    time.sleep(2)
    print("պակլոն "*3)

սկսենք երգել
շուդադի շուդադա վիզաութ յոռ լավ
պակլոն պակլոն պակլոն 
Duration: 2.0101306438446045 seconds

Պրոեկտի համար թիմերի բաժանվել

import random

TEAM_SIZE = 3
teams = []
lst = [f"Մարդ {i}" for i in range(1, 11)]
# 3 player teams
random.shuffle(lst)

num_players = len(lst)
num_teams = num_players / 3

print(f"Num players: {len(lst)}")
print(f"Num teams: {num_teams}")

if num_players % num_teams != 0:
    num_teams = int(num_teams) + 1

print(num_players % num_teams)
if num_players % TEAM_SIZE == 1:
    num_teams -= 2
    
print(num_teams)
for i in range(num_teams):
    print(lst[3*i:3*(i+1)])
    
if num_players % TEAM_SIZE == 1:
    print(lst[-4:-2])
    print(lst[-2:])

Num players: 10
Num teams: 3.3333333333333335
2
2
['Մարդ 5', 'Մարդ 6', 'Մարդ 3']
['Մարդ 8', 'Մարդ 7', 'Մարդ 10']
['Մարդ 9', 'Մարդ 1']
['Մարդ 2', 'Մարդ 4']