• open() function opens the file and returns a file object.
• tell() function tells the current cursor position.
• seek() function allows us to change the cursor position.
• close() function closes the file.
• The program will also run perfectly if we don’t close a file. But closing a file is a good practice.

f = open('File1.txt')
print(f"Curser position is - {f.tell()}")
print(f.read())
print(f"Curser position is - {f.tell()}")
print(f"Before seek method, cursor position was at - {f.tell()}")
f.seek(0)
print(f"After seek method, cursor position is at - {f.tell()}")
print(f.read())
f.close()

OUTPUT :

Curser position is - 0
Hey, I'm Sayan Dey.
I'm from Chandannagar.
My emai id is - d.sayan1998@gamil.com.
There's a big pandemic situation in the world. Hope everyone is okay.
Stay at home.
Stay safe.
Use sanitizers.
Use hand gloves.
Use handwashes.
Curser position is - 233
Before seek method, cursor position was at - 233
After seek method, cursor position is at - 0
Hey, I'm Sayan Dey.
I'm from Chandannagar.
My emai id is - d.sayan1998@gamil.com.
There's a big pandemic situation in the world. Hope everyone is okay.
Stay at home.
Stay safe.
Use sanitizers.
Use hand gloves.
Use handwashes.

CONTENT OF MY FILE :

Hey, I’m Sayan Dey.
I’m from Chandannagar.
My emai id is – d.sayan1998@gamil.com.
There’s a big pandemic situation in the world. Hope everyone is okay.
Stay at home.
Stay safe.
Use sanitizers.
Use hand gloves.
Use handwashes.

• l – Basically a pointer that points which line is current being executed.
• n – Executes the line.
• c – Continues the code without further debugging.
• q – Quits debugging.

import pdb

pdb.set_trace()
name = input("Enter your name : ")
age = input("Enter your age : ")
print(f"You have entered {name} and {age}")
age = age + 5
print("You'll be {age} in the after 5 years")





P.S : THIS CODE IS WRONG. THIS CODE IS INTENTIONALLY WRITTEN WRONG TO DEBUG IT. DON'T COPY. THE CORRECT CODE IS PROVIDED BELOW THE OUTPUT.

OUTPUT :

> c:\users\dsaya\onedrive\desktop\pythonpractise\oop\debuggin_in_python.py(4)<module>()
-> name = input("Enter your name : ")
(Pdb) l
  1     import pdb
  2
  3     pdb.set_trace()
  4  -> name = input("Enter your name : ")
  5     age = input("Enter your age : ")
  6     print(f"You have entered {name} and {age}")  
  7     age = age + 5
  8     print("You'll be {age} in the after 5 years")
[EOF]
(Pdb) n
Enter your name : Sayan
> c:\users\dsaya\onedrive\desktop\pythonpractise\oop\debuggin_in_python.py(5)<module>()
-> age = input("Enter your age : ")
(Pdb) n
Enter your age : 22
> c:\users\dsaya\onedrive\desktop\pythonpractise\oop\debuggin_in_python.py(6)<module>()
-> print(f"You have entered {name} and {age}")
(Pdb) n
You have entered Sayan and 22
> c:\users\dsaya\onedrive\desktop\pythonpractise\oop\debuggin_in_python.py(7)<module>()
-> age = age + 5
(Pdb) n
TypeError: can only concatenate str (not "int") to str
> c:\users\dsaya\onedrive\desktop\pythonpractise\oop\debuggin_in_python.py(7)<module>()
-> age = age + 5
(Pdb) q
Traceback (most recent call last):
  File "c:/Users/dsaya/OneDrive/Desktop/PythonPractise/OOP/Debuggin_In_Python.py", line 7, in <module>
    age = int(age) + 5
  File "C:\Python385\lib\bdb.py", line 94, in trace_dispatch
    return self.dispatch_exception(frame, arg)
  File "C:\Python385\lib\bdb.py", line 174, in dispatch_exception
    if self.quitting: raise BdbQuit
bdb.BdbQuit

CORRECT CODE :

import pdb

pdb.set_trace()
name = input("Enter your name : ")
age = input("Enter your age : ")
print(f"You have entered {name} and {age}")
age = age + 5
print("You'll be {age} in the after 5 years")

class NameTooShort(ValueError):
    pass
def check(name):
    if len(name)<5:
        raise NameTooShort("Your name is too short")
    
name = input("Enter the name : ")
check(name)
print(f"Hello {name}")

def divide(a, b):
    try:
        return a/b
    except ZeroDivisionError:
        return("Division by zero isn't possible")
    except TypeError:
        return("Unsupported type error")

print(divide(10, 3))

• If try throws an error then except executes.
• If try doesn’t throw an error then else part executes.
• The finally block executes always. Error doesn’t matter here.

while True:
    try:
        age = int(input("Enter the age to check eligibility : "))
        break
    except ValueError:
        print("Please enter an integer")
    except:
        print("Unexpected error")
    else:
        print(f"User has entered {age}")
    finally:
        print("This is a program to verify age")

if age>18:
    print("You are eligible to play")
else:
    print("You aren't eligible to play")

while True:
    try:
        age = int(input("Enter the number to check eligibility : "))
        break
    except ValueError:
        print("You might have entered string. Try integer value. Try again please...")
    except:
        print("Unexpected error")

if(age>18):
    print("You are eligibile to play the game!!")
else:
    print("You are not eligible to play the game!!")

• There are no abstract methods in Python.
• The name came from JAVA Programming Language. But we can raise error to implement that kind of methods in Python too.

class Phone:
    def __init__(self, brand, model):
        self.brand = brand
        self.model = model

    def cameraa(self):
        raise NotImplementedError("This method must be defined in each and every subclass")

class SmartPhone(Phone):
    def __init__(self, brand, model, camera):
        super().__init__(brand, model)
        self.camera = camera

class FlagshipPhone(Phone):
    def __init__(self, brand, model, front_camera, rear_camera):
        super().__init__(brand, model)
        self.front_camera = front_camera
        self.rear_camera = rear_camera

S = SmartPhone("POCO", "X2", "64MP")
print(S.cameraa())

OUTPUT :

Traceback (most recent call last):
  File "c:/Users/dsaya/OneDrive/Desktop/PythonPractise/OOP/RaiseError.py", line 21, in <module>
    print(S.cameraa())
  File "c:/Users/dsaya/OneDrive/Desktop/PythonPractise/OOP/RaiseError.py", line 7, in cameraa  
    raise NotImplementedError("This method must be defined in each and every subclass")        
NotImplementedError: This method must be defined in each and every subclass

class Phone:
    def __init__(self, brand, model_name, price):
        self.brand = brand
        self.model_name = model_name
        self.price = price
        
    def full_name(self):
        return f"This phone is {self.brand} {self.model_name}"
    
    def make_a_call(self, number):
        return f"Dialling {number}..."

class Smartphone(Phone):
    def __init__(self, brand, model_name, price, ram, internal_memory, rear_camera):
        super().__init__(brand, model_name, price)
        # Phone.__init__(self, brand, model_name, price)
        self.ram = ram
        self.internal_memory = internal_memory
        self.rear_camera = rear_camera

    def full_name(self):
        return f"This phone is {self.brand} {self.model_name} and it has a rear camera of {self.rear_camera}"

class Flagshipphone(Smartphone):
    def __init__(self, brand, model_name, price, ram, internal_memory, rear_camera, front_camera):
        super().__init__(brand, model_name, price, ram, internal_memory, rear_camera)
        self.front_camera = front_camera

    def full_name(self):
        return f"This phone is {self.brand} {self.model_name} and it has a front camera of {self.front_camera}"

    def __str__(self):
        return f"{self.brand} {self.model_name}"

    def __repr__(self):
        return f"{self.brand} {self.model_name}" 

    def __len__(self):
        return len(self.full_name())

    def __add__(self, other):
        return int(self.price) + int(other.price)



S1 = Flagshipphone("OnePlus", "8 Pro", "75000", "8GB", "256GB", "64MP", "32MP")
S2 = Flagshipphone("OnePlus", "7 Pro", "76000", "8GB", "256GB", "64MP", "32MP")
# S2 = Flagshipphone("OnePlus", "8 Pro", "75000", "8GB", "256GB", "64MP", "32MP")
# print(S2.full_name())
# print(help(Smartphone))
# print(S1.__repr__())
# print(str(S1))
print(S1.__len__())
print(S1 + S2)

• This is something that is mostly not used by developers due to the confusion it causes.
• It has a main problem with order. In the order, which comes first will be called first.
• As in the example below, if we want to print the hello method of Class B, we need to inherit the B class first from the C class.

class A:
    def class_a_method(self):
        return "This is a method of Class A"
    
    def hello(self):
        return "Returning from Class A"

class B:
    def class_a_method(self):
        return "This is a method of Class A"
    
    def hello(self):
        return "Returning from Class B"

class C(A, B):
    pass

objC = C()

print(objC.hello())

print((help(C))

OUTPUT:

Returning from Class A
Help on class C in module __main__:

class C(A, B)
 |  Method resolution order:
 |      C
 |      A
 |      B
 |      builtins.object
 |
 |  Methods inherited from A:
 |
 |  class_a_method(self)
-- More  --