Python Coding challenge - Day 395| What is the output of the following Python Code?

 

Step-by-Step Execution:

Importing SymPy Functions

symbols('x'): Creates a symbolic variable x that can be used in algebraic equations.

solve(eq, x): Finds values of x that satisfy the equation.

Equation Definition

eq = x**2 - 4 represents the quadratic equation:

Solving the Equation

The equation can be factored as:

(x−2)(x+2)=0

Setting each factor to zero:

x−2=0⇒x=2

x+2=0⇒x=−2

Output of solve(eq, x)

solve(eq, x) returns a list of solutions:

[2, -2]

This means the equation has two real roots: x = 2 and x = -2.

Final Output

[2, -2]

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Python Coding challenge - Day 394| What is the output of the following Python Code?

 Step-by-Step Explanation

Create a Black Image

img = np.zeros((100, 100, 3), dtype=np.uint8)

np.zeros((100, 100, 3), dtype=np.uint8) creates a black image of size 100x100 pixels.

The 3 at the end means it has 3 color channels (Blue, Green, Red - BGR).

Since it's all zeros, the image is completely black.

Convert to Grayscale

gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)

cv2.cvtColor(img, cv2.COLOR_BGR2GRAY) converts the BGR image to grayscale.

Grayscale images have only 1 channel instead of 3.

Each pixel in grayscale has an intensity value (0 to 255) instead of 3 separate color values.

Print the Shape

print(gray.shape)

The original image (img) has a shape of (100, 100, 3), meaning 3 color channels.

The converted grayscale image (gray) now has a shape of (100, 100), because it has only one channel (intensity values instead of color).

Final Output

(100, 100)

This confirms that the grayscale image has only height and width dimensions, with no color channels.

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Python Coding challenge - Day 391| What is the output of the following Python Code?

 

Step-by-Step Explanation

1. Importing create_engine

from sqlalchemy import create_engine

create_engine is a function in SQLAlchemy that creates a database engine.

This engine serves as the core interface between Python and the database.

2. Creating an In-Memory SQLite Database

engine = create_engine("sqlite:///:memory:")

"sqlite:///:memory:" tells SQLite to create a temporary, in-memory database.

This means:

The database only exists in RAM.

It disappears once the script stops running.

No .db file is created.

3. Establishing a Connection

conn = engine.connect()

This opens a connection to the SQLite database.

The connection allows you to execute SQL queries.

4. Retrieving Table Names

print(engine.table_names())

Purpose: It attempts to list all tables in the database.

Problem: engine.table_names() is deprecated in SQLAlchemy 1.4+.

Alternative for SQLAlchemy 1.4+

Instead of engine.table_names(), use:

from sqlalchemy import inspect

inspector = inspect(engine)

print(inspector.get_table_names())  # Recommended

This is the correct way to retrieve table names in modern SQLAlchemy versions.

Final Output:

Since we haven't created any tables, the output will be:

[]

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Python Coding challenge - Day 386| What is the output of the following Python Code?

 

Step-by-Step Execution:

1. Import weakref Module

The weakref module in Python allows the creation of weak references to objects.

A weak reference does not prevent an object from being garbage collected.

2. Define the Node Class

The Node class has:

__init__: Initializes self.value with the given argument.

__repr__: Defines a string representation for the object (Node(value)).

3. Create a Node Object

node = Node(10)

Creates an instance of Node with value = 10.

node is now a strong reference to the object.

4. Create a Weak Reference

weak_node = weakref.ref(node)

weak_node is a weak reference to node.

This means weak_node does not increase the reference count of node, and it won't prevent garbage collection.

5. Print the Weak Reference

print(weak_node()) 

Calling weak_node() dereferences it, returning the actual Node(10) object if it is still alive.

Since node is still strongly referenced, the output is:

Node(10)

Final Output:

Node(10)

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Python Coding challenge - Day 384| What is the output of the following Python Code?

 

Explanation:

Class A Definition:

A is a class that has a method show() which returns the string "A".

Class B Definition:

B is a subclass of A (class B(A):), meaning B inherits everything from A.

The keyword pass is used, which means B does not introduce any new attributes or methods—it simply inherits from A.

Creating an Instance of B:

B() creates an object of class B.

Calling show() on an Instance of B:

print(B().show()):

Since B does not have its own show() method, it looks up the method in its parent class (A).

The show() method of A is executed, returning "A".

Output:

A

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Python Coding challenge - Day 383| What is the output of the following Python Code?

 

Step by Step Explanation:

Step 1: Define Class A

A class named A is created.

Inside A, we define a method show():

When called, this method returns the string "A".

Any object of A can call show() and get "A".

class B(A):

    pass

Step 2: Define Class B (Inheritance)

B is inheriting from A, meaning B gets all the attributes and methods of A.

The keyword pass means no additional methods or properties are added to B.

Since B does not have its own show() method, it will inherit the method from A.

print(B().show())

Step 3: Create an Object of B and Call show()

B() creates an instance of class B.

B().show() calls the show() method.

Since B does not have a show() method, it looks in class A (its parent class).

The show() method in A is executed, returning "A".

The print() function prints the returned value.

Final Output

A

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Python Coding challenge - Day 382| What is the output of the following Python Code?

 

Step by Step Explanation:

def decorator(cls):

    cls.value = 42  # Adds a new attribute `value` to the class

    return cls  # Returns the modified class

Step 1: Define a Class Decorator

def decorator(cls):

This defines a function named decorator that takes a class (cls) as its parameter.

When applied, it will modify the class by adding new attributes or methods.

cls.value = 42

This adds a new attribute value to the class passed to the decorator.

Every class that uses @decorator will automatically have value = 42.

return cls

The modified class is returned.

This ensures that the original class remains functional but now has additional modifications.

@decorator  # Applying the decorator to the class

class Test:

    pass

Step 2: Apply the Decorator

@decorator

This applies the decorator function to the Test class.

Equivalent to manually writing:

class Test:

    pass

Test = decorator(Test)  # Modifies `Test` by adding `value = 42`When Test is passed into decorator(), it modifies Test by adding value = 42.

print(Test.value)  # Accessing the modified class attribute

Step 3: Print the New Attribute

Test.value

Since the decorator added value = 42, this now exists in the class.

print(Test.value) prints 42.

Final Output:

42

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Python Coding challenge - Day 381| What is the output of the following Python Code?

Code Explanation:

Importing Required Modules

from abc import ABC, abstractmethod  

ABC (Abstract Base Class) is imported from the abc module.

@abstractmethod is used to define an abstract method.

Defining an Abstract Class (P)

class P(ABC):  

    @abstractmethod  

    def calc(self, x):  

        pass  

P is an abstract class because it inherits from ABC.

calc(self, x) is an abstract method (it has no implementation).

Any subclass of P must override calc() before being instantiated.

Creating a Subclass (Q)

class Q(P):  

    def calc(self, x):  

        return x * 2  

Q inherits from P and provides an implementation for calc().

Since calc() is now implemented, Q is no longer abstract and can be instantiated.

Instantiating Q and Calling calc()

print(Q().calc(5))  

An object of Q is created: Q().

The calc(5) method is called, which returns 5 * 2 = 10.

Final Output

10

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Python Coding challenge - Day 380| What is the output of the following Python Code?

 

Code Explanation:

Importing Required Modules

from abc import ABC, abstractmethod  

ABC (Abstract Base Class) is imported from the abc module.

@abstractmethod is used to define an abstract method.

Defining an Abstract Class (A)

class A(ABC):  

    @abstractmethod  

    def show(self):  

        pass  

A is an abstract class because it inherits from ABC.

show(self) is an abstract method, meaning any subclass must override it before being instantiated.

Since show() has no implementation (pass), A cannot be instantiated directly.

Creating a Subclass (B)

class B(A):  

    pass  

B is a subclass of A, but it does not implement the show() method.

Because show() is still missing, B remains an abstract class.

Python does not allow instantiating an abstract class, so obj = B() causes an error.

Attempting to Instantiate B

obj = B()  

Final Output:

Implement show() in B

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Python Coding challenge - Day 379| What is the output of the following Python Code?

 

Code Explanation:

Importing Required Modules

from abc import ABC, abstractmethod  

ABC (Abstract Base Class) is imported from the abc module.

@abstractmethod is used to define an abstract method.

Defining an Abstract Class (X)

class X(ABC):  

    @abstractmethod  

    def display(self):  

        pass  

X is an abstract class because it inherits from ABC.

display(self) is marked as an abstract method using @abstractmethod.

Since display() has no implementation (pass), any subclass of X must override it to be instantiated.

Creating a Subclass (Y)

class Y(X):  

    pass  

Y is a subclass of X, but it does not implement the display() method.

Because display() is still missing, Y remains abstract and cannot be instantiated.

Attempting to Instantiate Y

obj = Y()  

Since Y does not provide an implementation for display(), it remains an abstract class.

Python does not allow instantiating an abstract class, so this line raises a TypeError.

Final Output:

TypeError

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Python Coding challenge - Day 377| What is the output of the following Python Code?

Code Explanation 

class Meta(type):

    pass

Defines a custom metaclass Meta, which inherits from type.

In Python, metaclasses control how classes are created.

Meta is now a metaclass, meaning it can be used to define new classes.

class A(metaclass=Meta):

    pass

Defines a new class A using Meta as its metaclass.

Normally, Python uses type as the default metaclass.

Here, A is created using Meta instead of type, meaning:

Meta is responsible for handling the creation of A.

A is now an instance of Meta, instead of type.

print(type(A))

Prints the type of A

Since A was created using Meta, the result will be:

Final Output:

<class '__main__.Meta'>

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Python Coding challenge - Day 376| What is the output of the following Python Code?

 

Code Explanation 

class Meta(type):

    def __init__(cls, name, bases, dct):

        print("Initializing:", name)

Defines a custom metaclass Meta, which inherits from type.

__init__ is a special method that is called when a class is created.

Parameters of __init__:

cls → The class being created (e.g., A).

name → Name of the class being created ("A" in this case).

bases → Tuple of base classes (() since A has no parent class).

dct → Dictionary containing class attributes and methods.

The print() statement executes when the class is created, not when an object is instantiated.

class A(metaclass=Meta):

    pass

Defines class A using Meta as its metaclass.

Since Meta is the metaclass, Python calls Meta.__init__ to initialize A.

The print() statement inside Meta.__init__ runs immediately.

Output:

Initializing: A

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Python Coding challenge - Day 375| What is the output of the following Python Code?

Code Explanation 

class Meta(type):

    pass

Defines a custom metaclass Meta

Meta inherits from type, which means it is a metaclass.

A metaclass is a class that defines how other classes are created.

class A(metaclass=Meta):

    pass

Defines a class A using Meta as its metaclass.

Normally, Python uses type as the default metaclass.

Here, Meta replaces type, meaning Meta controls the creation of A.

print(type(A))

Prints the type of A

Since A was created using Meta, type(A) will return Meta.

Final Output:

<class '__main__.Meta'>

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Python Coding challenge - Day 374| What is the output of the following Python Code?

 

Code Explanation 

import weakref

Imports the weakref module, which allows creating weak references and proxies to objects.

class A:  

    x = 10

Defines a class A with a class attribute x = 10.

This means any instance of A will have access to x.

obj = A()

Creates an instance obj of class A, which is a strong reference to the object.

Since obj is a strong reference, the object will not be garbage collected yet.

proxy = weakref.proxy(obj)

Creates a weak reference proxy proxy to obj using weakref.proxy(obj).

Unlike weakref.ref(), which requires calling (wref()),

a proxy behaves like the original object (i.e., proxy.x is the same as obj.x).

del obj

Deletes the strong reference obj.

Since there are no strong references left, the object is garbage collected.

The weak reference proxy (proxy) is now pointing to a deleted object.

print(proxy.x)

Now, proxy.x raises an error because obj no longer exists.

Since proxy is just a reference, it does not keep obj alive.

Accessing attributes of a deleted object causes a ReferenceError.

Final Output: 

C: Raises ReferenceError

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Python Coding challenge - Day 373| What is the output of the following Python Code?

 

Code Explanation 

import weakref

Imports the weakref module, which allows creating weak references to objects.

class A: pass

Defines a simple class A with no attributes or methods.

obj = A()

Creates an instance obj of class A, which is a strong reference to the object.

Since obj is a strong reference, the object will not be garbage collected while obj exists.

wref = weakref.ref(obj)

Creates a weak reference wref to obj using weakref.ref(obj).

A weak reference does not prevent garbage collection of the object.

wref is a callable weak reference, meaning we must call wref() to access the original object.

print(wref() is obj)

Checks if wref() returns the same object as obj.

wref() calls the weak reference and returns the original object (obj).

Since obj is still alive, wref() returns the same object as obj

Final Answer:

True

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Python Coding challenge - Day 372| What is the output of the following Python Code?

 

Code Explanation 

import weakref  

Imports the weakref module, which allows creating weak references to objects.

Weak references let Python track an object without preventing garbage collection (i.e., if there are no strong references left, the object is deleted).

class MyClass:  

    pass  

 Defines a simple class MyClass with no attributes or methods.

This is just a placeholder class to create objects.

obj = MyClass()  

Creates an instance obj of MyClass.

obj is a strong reference, meaning it keeps the object alive.

weak_obj = __________(obj)  

Creates a weak reference to obj using a function from the weakref module.

Final Output:

B) weakref.ref()

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Python Coding challenge - Day 371| What is the output of the following Python Code?

Step-by-Step Execution:

Importing nullcontext from contextlib:

nullcontext is a do-nothing context manager.

It is useful when you need a placeholder for a context manager but don’t actually need to manage any resources.

Using with nullcontext():

The nullcontext() context manager does not change the execution flow.

It behaves as if the with statement isn't there.

Executing print("Inside block"):

Since nullcontext() does nothing, "Inside block" is printed normally.

Expected Output:

Inside block

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Python Coding challenge - Day 370| What is the output of the following Python Code?

Step-by-Step Execution:

Importing suppress from contextlib:

suppress is a context manager that allows us to ignore specific exceptions.

Using with suppress(ZeroDivisionError):

The with block will execute normally, and if a ZeroDivisionError occurs inside it, it will be suppressed.

Executing print("No Error"):

This simply prints "No Error", which does not raise any exception.

Since no exception occurs, the suppress block has no effect.

If there were a ZeroDivisionError, it would be ignored, but no such error happens here.

Executing print("After block"):

The program continues execution and prints "After block".

Expected Output:

No Error

After block

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Python Coding challenge - Day 369| What is the output of the following Python Code?

 

Step-by-Step Execution:

Importing suppress from contextlib:

suppress is a context manager that is used to ignore specified exceptions.

Using with suppress(FileNotFoundError):

The with block executes normally.

If a FileNotFoundError occurs inside the block, it is silenced (ignored) instead of raising an error.

Attempting to Open a Non-Existent File (open("non_existent.txt")):

Since "non_existent.txt" does not exist, Python normally raises a FileNotFoundError.

However, because of suppress(FileNotFoundError), the error is ignored, and execution continues.

Executing print("After with block"):

Since the exception is suppressed, the program does not crash.

The statement "After with block" is printed.

Output:

After with block

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Python Coding challenge - Day 368| What is the output of the following Python Code?

 

Step-by-Step Execution:

Opening the File (open("test.txt", "w")):

The open() function is used to open the file "test.txt" in write mode ("w").

If the file "test.txt" doesn't exist, it will be created.

If the file already exists, its content will be overwritten.

Writing to the File (file.write("Hello!")):

The write() method writes "Hello!" to the file.

This does not automatically close the file.

Closing the File (file.close()):

The close() method closes the file.

Closing a file releases system resources and ensures the data is properly saved.

Checking if the File is Closed (print(file.closed))

file.closed is a boolean attribute that returns True if the file is closed, False otherwise.

Since we explicitly closed the file with file.close(), file.closed will return True.

Output:

True

This confirms that the file is successfully closed.

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