Python Variables Definition Creation Casting Getting the Type of a Variable Case Sensitivity Output Local Global Variable Inside a Function Numbers

Definition of Variables

1. Variables are Containers
   • Used for storing data values.

---

Creating Variables

1. No Declaration Command

   • Python does not require a specific command to declare variables.
   • A variable is created when you assign a value to it.

2. Examples:

   • x = 5
     y = "John"
     print(x)
     print(y)
     

3. Dynamic Typing

   • Variables do not need to have a fixed type and can change types after being set.
   • Example:

     x = 4       # x is of type int
     x = "Sally" # x is now of type str
     print(x)
     

---

Casting Variables

1. Specifying Data Type
   • Use casting to define a variable's data type explicitly.
   • Example:

     x = str(3)    # x will be '3'
     y = int(3)    # y will be 3
     z = float(3)  # z will be 3.0
     

---

Getting the Type of a Variable

1. Using type() Function
   • Check the data type of a variable.
   • Example:

     x = 5
     y = "John"
     print(type(x))  # Output: <class 'int'>
     print(type(y))  # Output: <class 'str'>
     

---

Strings and Quotes

1. Single or Double Quotes
   • String variables can use either single (') or double (") quotes interchangeably.
   • Example:

     x = "John"
     y = 'John'
     

---

Case Sensitivity

1. Variable Names are Case-Sensitive
   • Variables with different cases are treated as distinct variables.
   • Example:

     a = 4
     A = "Sally"
     # A will not overwrite a
     

---

Exercise

• Question: What is a correct way to declare a Python variable?
  • Correct Answer: x = 5

---

Definition of Variable Names

1. Short or Descriptive
   • Variable names can be short (e.g., x, y) or descriptive (e.g., age, carname, total_volume).

---

Rules for Python Variable Names

1. Starting Character

   • Must start with a letter or an underscore (_).

2. Cannot Start with a Number

   • A variable name cannot begin with a digit.

3. Allowed Characters

   • Can only contain alphanumeric characters (A-Z, a-z, 0-9) and underscores (_).

4. Case Sensitivity

   • Variable names are case-sensitive. Examples:
     • age, Age, and AGE are treated as different variables.

5. Python Keywords

   • Variable names cannot be any of Python's reserved keywords.

---

Examples of Legal and Illegal Variable Names

Legal Variable Names:

myvar = "John"
my_var = "John"
_my_var = "John"
myVar = "John"
MYVAR = "John"
myvar2 = "John"

Illegal Variable Names:

2myvar = "John"  # Cannot start with a number
my-var = "John"  # Cannot contain special characters like "-"
my var = "John"  # Cannot contain spaces

---

Reminder

• Case Sensitivity:
  • Variable names like myvar, MyVar, and MYVAR are distinct due to Python's case sensitivity.

---

---

Many Values to Multiple Variables

1. Assigning Multiple Values in One Line

   • Python allows assigning multiple values to multiple variables in one line.
   • Example:

     x, y, z = "Orange", "Banana", "Cherry"
     print(x)  # Orange
     print(y)  # Banana
     print(z)  # Cherry
     

2. Matching Variables and Values

   • The number of variables must match the number of values; otherwise, an error will occur.

---

One Value to Multiple Variables

1. Assigning the Same Value to Multiple Variables
   • A single value can be assigned to multiple variables in one line.
   • Example:

     x = y = z = "Orange"
     print(x)  # Orange
     print(y)  # Orange
     print(z)  # Orange
     

---

Unpack a Collection

1. Extracting Values from Collections

   • Python allows extracting values from a collection (like a list or tuple) into variables, called unpacking.
   • Example:

     fruits = ["apple", "banana", "cherry"]
     x, y, z = fruits
     print(x)  # apple
     print(y)  # banana
     print(z)  # cherry
     

2. Learn More About Unpacking

   • You can learn more about unpacking in the Unpack Tuples Chapter.

---

Exercise

Question:
What is the correct syntax to assign the value 'Hello World' to 3 variables in one statement?

Options:

1. x, y, z = 'Hello World'
2. x = y = z = 'Hello World' ✅
3. x|y|z = 'Hello World'

---

Output Variables

1. Using print() to Output Variables

   • The print() function can be used to display the value of a variable.
   • Example:

     x = "Python is awesome"
     print(x)
     

2. Outputting Multiple Variables

   • Multiple variables can be output using commas within the print() function.
   • Example:

     x = "Python"
     y = "is"
     z = "awesome"
     print(x, y, z)  # Python is awesome
     

3. Using the + Operator to Output Variables

   • The + operator can be used to concatenate strings.
   • Example:

     x = "Python "
     y = "is "
     z = "awesome"
     print(x + y + z)  # Python is awesome
     

   • Note: If there are no spaces within the string variables, the result will appear as a single concatenated string (e.g., "Pythonisawesome").

---

Working with Numbers

1. Mathematical Operation with +

   • The + operator adds numbers when used with numeric variables.
   • Example:

     x = 5
     y = 10
     print(x + y)  # 15
     

2. Error When Combining Strings and Numbers

   • Combining a string and a number with the + operator will result in a TypeError.
   • Example:

     x = 5
     y = "John"
     print(x + y)  # Error
     

3. Using Commas for Different Data Types

   • Using commas in the print() function allows you to combine different data types.
   • Example:

     x = 5
     y = "John"
     print(x, y)  # 5 John
     

---

Exercise

Question:
Consider the following code:

print('Hello', 'World')

What will be the printed result?

Options:

1. Hello, World
2. Hello World ✅
3. HelloWorld

Global Variables

---

Definition of Global Variables

1. Global Variables are created outside of a function and can be used both inside and outside of functions.

---

Using Global Variables Inside Functions

2. A global variable can be accessed directly within a function.
   • Example:

     x = "awesome"
     
     def myfunc():
         print("Python is " + x)
     
     myfunc()  # Output: Python is awesome
     

---

Local Variables with the Same Name as Global Variables

3. If a variable with the same name as a global variable is defined inside a function, it becomes a local variable and does not affect the global variable.
   • Example:

     x = "awesome"
     
     def myfunc():
         x = "fantastic"  # Local variable
         print("Python is " + x)
     
     myfunc()              # Output: Python is fantastic
     print("Python is " + x)  # Output: Python is awesome
     

---

The global Keyword

4. Definition: The global keyword is used to define or modify a global variable inside a function.

---

Creating a Global Variable Inside a Function

5. Using global within a function creates a global variable that can be accessed outside of the function.
   • Example:

     def myfunc():
         global x
         x = "fantastic"
     
     myfunc()
     print("Python is " + x)  # Output: Python is fantastic
     

---

Modifying a Global Variable Inside a Function

6. To change the value of an existing global variable inside a function, use the global keyword.
• Example:

  x = "awesome"
  
  def myfunc():
      global x
      x = "fantastic"
  
  myfunc()
  print("Python is " + x)  # Output: Python is fantastic
  

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Python script to develop a simple Student Exam Result Sheet App

If you're a beginner and want a simple way to handle subjects without using functions or loops, you can write the script like this:

Simplified Script:

# Welcome message
print("Welcome to the Student Exam Result Sheet App!")

# Input student details
name = input("Enter Student's Name: ").strip()
student_class = input("Enter Student's Class: ").strip()

# Input marks for each subject
math = float(input("Enter marks for Math: "))
science = float(input("Enter marks for Science: "))
history = float(input("Enter marks for History: "))
geography = float(input("Enter marks for Geography: "))
it = float(input("Enter marks for IT: "))

# Calculate total marks
total_marks = math + science + history + geography + it

# Print the result sheet
print("\n---- Student Exam Result Sheet ----")
print(f"Name: {name}")
print(f"Class: {student_class}")
print("\nSubjects and Marks:")
print(f"Math: {math}")
print(f"Science: {science}")
print(f"History: {history}")
print(f"Geography: {geography}")
print(f"IT: {it}")
print("\nTotal Marks:", total_marks)
print("-----------------------------------")

How It Works:

1. Input Student Details:

   • Asks for the student's name and class.

2. Input Marks for Each Subject:

   • Collects marks for "Math," "Science," "History," "Geography," and "IT" directly without using a loop.

3. Calculate Total Marks:

   • Adds the marks of all subjects using simple arithmetic.

4. Display the Result Sheet:

   • Prints the student details, each subject's marks, and the total marks in a readable format.

Example Input/Output:

Input:

Enter Student's Name: John Doe
Enter Student's Class: Grade 6
Enter marks for Math: 85
Enter marks for Science: 90
Enter marks for History: 75
Enter marks for Geography: 80
Enter marks for IT: 88

Output:

---- Student Exam Result Sheet ----
Name: John Doe
Class: Grade 6

Subjects and Marks:
Math: 85.0
Science: 90.0
History: 75.0
Geography: 80.0
IT: 88.0

Total Marks: 418.0
-----------------------------------

Why It’s Beginner-Friendly:

1. No Functions or Loops: The script directly asks for each subject's marks and calculates the total.
2. Step-by-Step: Each part of the script is written in a straightforward, sequential manner.
3. Easily Expandable: To add more subjects, just add another input line and include it in the total.

Let me know if you'd like further simplifications or explanations!

========

Here's a Python script to develop a simple Student Exam Result Sheet App. The script will:

1. Take input for the student's name and class.
2. Take input for marks in each subject (Math, Science, History, Geography, IT).
3. Calculate the total marks.
4. Print the result sheet with the student's details, marks for each subject, and total marks.

Here's the complete Python script:

# Student Exam Result Sheet App

def get_student_details():
    """Get student's name and class"""
    name = input("Enter Student's Name: ").strip()
    student_class = input("Enter Student's Class: ").strip()
    return name, student_class

def get_subject_marks():
    """Get marks for all subjects"""
    subjects = ["Math", "Science", "History", "Geography", "IT"]
    marks = {}
    
    print("\nEnter marks for the following subjects:")
    for subject in subjects:
        while True:
            try:
                mark = float(input(f"{subject}: "))
                if 0 <= mark <= 100:  # Validating mark range
                    marks[subject] = mark
                    break
                else:
                    print("Marks should be between 0 and 100. Please try again.")
            except ValueError:
                print("Invalid input! Please enter a valid number.")
    return marks

def calculate_total_marks(marks):
    """Calculate the total marks"""
    return sum(marks.values())

def display_result_sheet(name, student_class, marks, total_marks):
    """Display the result sheet"""
    print("\n---- Student Exam Result Sheet ----")
    print(f"Name: {name}")
    print(f"Class: {student_class}")
    print("\nSubjects and Marks:")
    for subject, mark in marks.items():
        print(f"{subject}: {mark:.2f}")
    print("\nTotal Marks:", total_marks)
    print("-----------------------------------")

def main():
    """Main function to run the app"""
    print("Welcome to the Student Exam Result Sheet App!")
    name, student_class = get_student_details()
    marks = get_subject_marks()
    total_marks = calculate_total_marks(marks)
    display_result_sheet(name, student_class, marks, total_marks)

if __name__ == "__main__":
    main()

How to Use the Script

1. Copy and paste the script into a Python IDE or a text editor (e.g., VS Code, PyCharm, or a simple text editor).
2. Save the file with a .py extension, e.g., student_result_sheet.py.
3. Run the script in your terminal or Python environment.
4. Follow the prompts to enter:
   • The student's name and class.
   • Marks for each subject (input between 0 and 100).
5. The script will display the result sheet.

Features

• Input validation ensures marks are between 0 and 100.
• Clear formatting for the result sheet.
• Easy-to-modify script (e.g., add more subjects).

You can extend this script by saving the results to a file (CSV or JSON) or using a database for persistent storage. Let me know if you'd like to add any advanced features!