Python — Basics

Functions, OOP, file handling, calculator, loops. #PurePythonSeries — Episode #17

Explore the basics of Python with this tutorial 
covering essential functions, object-oriented programming, 
and file handling. 

Learn how to create a simple calculator class, 
integrate it into a worksheet, 
and handle common exceptions. 

Plus, discover the difference between 
return and break in loops. 
Perfect for beginners or 
those looking to sharpen their Python skills!

Welcome!

👉️ Colab nb

1 Step — Functions:

def add(a, b):
  return a + b

def subtract(a, b):
  return a - b

def multiply(a, b):
  return a * b

def divide(a, b):
  return a / b

add(1, 2)
3

2 Step — Classes:

# prompt: generating a class from the methods above

class Calculator:
  def add(self, a, b):
    return a + b
    
  def subtract(self, a, b):
    return a - b
    
  def multiply(self, a, b):
    return a * b
    
  def divide(self, a, b):
    return a / b

if __name__ == "__main__":
  calculator = Calculator()
  print(calculator.add(1, 2))
  print(calculator.subtract(1, 2))
  print(calculator.multiply(1, 2))
  print(calculator.divide(1, 2))

3
-1
2
0.5

calculator = Calculator()
calculator.add(1, 2)

3

3Step — Objects:

# prompt: Generating a class Worksheet that use Calculator

class Worksheet:
  def __init__(self):
    self.calculator = Calculator()
    
    
  def perform_operations(self, a, b):
    print("Addition:", self.calculator.add(a, b))
    print("Subtraction:", self.calculator.subtract(a, b))
    print("Multiplication:", self.calculator.multiply(a, b))
    print("Division:", self.calculator.divide(a, b))

# Example usage:
worksheet = Worksheet()
worksheet.perform_operations(10, 5)

Addition: 15
Subtraction: 5
Multiplication: 50
Division: 2.0

worksheet.perform_operations(5, 10)

Addition: 15
Subtraction: -5
Multiplication: 50
Division: 0.5

4Step — Open Files; Use open():

  def open_file(filename):
    try:
      file = open(filename, 'r')
      contents = file.read()
      print(contents)
    except FileNotFoundError:
      print(f"File '{filename}' not found.")
    except Exception as e:
      print(f"An error occurred: {e}")
    finally:
      if 'file' in locals():
        file.close()

or with open():

# prompt: Generating a method to read a file use with open()

def read_file(filename):
    try:
      with open(filename, 'r') as file:
        contents = file.read()
        print(contents)
    except FileNotFoundError:
      print(f"File '{filename}' not found.")
    except Exception as e:
      print(f"An error occurred: {e}")
    finally:
      if 'file' in locals():
        file.close()

read_file("sample_data/worksheet.py")

It will create a file inside in this directory.

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5Step — Input Data:

 def enter_number():
    while True:
      try:
        number = float(input(f"Enter a number: "))      
      except ValueError:
        print("Invalid input.")
        
      except Exception as e:
        print(f"An error occurred: {e}  ")
        continue
      else:
        return number
        break

  enter_number()

Enter a number: w
Invalid input.
Enter a number: 1
1.0

Another without continue/break :

  def enter_number():
    while True:
      try:
        number = float(input(f"Enter a number: "))      
      except ValueError:
        print("Invalid input. Enter a number:")
      except Exception as e:
        print(f"An error occurred: {e}  ")
      else:
        return number

enter_number()

Enter a number: w
Invalid input. Enter a number:
Enter a number: 
Invalid input. Enter a number:
Enter a number: w
Invalid input. Enter a number:
Enter a number: 1
1.0

6Step — Diff Return x Break:

# Difference between Return and Break statements:
# https://stackoverflow.com/questions/6620949/difference-between-return-and-break-statements

# break is used to exit (escape) the for-loop, while-loop, 
# switch-statement that you are currently executing.

# return will exit the entire method you are currently executing 
#  (and possibly return a value to the caller, optional).

def f():
  while True:
    if x == 0:
      break # escape while() and jump to execute code after the loop
    elif x == 1:
      print("Returning imediatelly")
      print("Outside the f()")
      return # will end the function f() immediately
    # no further code inside this method will be executed.
    # ... other code to execute within the loop ...
  
  # Code to execute after the loop (if x == 0)
  print("Loop exited from while with break.")
  print("Inside the f()")
  print("You can now write a function (f()) to define its purpose")

x = 1
f()

Returning imediatelly
Outside the f()

x = 0
f()

Loop exited from while with break.
Inside the f()
You can now write a function (f()) to define its purpose

print("That's it folks!")

That's it folks!

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