Unit 6 - VrosCode

1. What is file? Enlist types of files in Python programming.

In Python, a file is a named location on disk that is used to store data permanently. It can be a text file, binary file, or a standard input/output device. Python provides several functions and modules to work with files, which allows reading and writing data to and from files.

There are several types of files in Python programming, including:

Text files: These are the most common type of files that store data in the form of text. They can be read and written using simple text editors or Python's built-in functions such as open() and read().
Binary files: These files store data in binary format, such as images, audio, or video files. They cannot be read using a simple text editor and require special software to open and view the data.
JSON files: These files store data in JSON (JavaScript Object Notation) format, which is a lightweight data interchange format. They are commonly used to store configuration data or exchange data between web servers and clients.
CSV files: These files store data in comma-separated values format, which is a simple text format for storing tabular data. They are commonly used in data analysis and machine learning applications.
XML files: These files store data in XML (Extensible Markup Language) format, which is a flexible and widely used markup language. They are commonly used to store and exchange data between web services.
SQLite databases: These files store data in a lightweight SQL database format. They can be used for small-scale data storage and manipulation.
Excel files: These files store data in Excel spreadsheet format. They are commonly used for data analysis and reporting.

Overall, Python provides a rich set of tools and libraries for working with different types of files, making it a powerful tool for data analysis, automation, and scientific computing.

2. What is exception?

In Python, an exception is an event that interrupts the normal flow of the program's execution. It is an error that occurs during the execution of a program and can be caused by various reasons such as incorrect input, division by zero, or trying to access an undefined variable. When an exception occurs, it causes the program to stop and Python raises an exception object that contains information about the error, such as the type of the exception and the line number where it occurred. Exception handling is the process of handling these errors gracefully, by taking appropriate actions to recover from the error and continue executing the program.

3. Explain the term exception handling in detail.

Exception handling is a mechanism in programming that enables a program to gracefully handle errors and unexpected situations. When an error occurs during program execution, the program throws an exception which can be caught and handled by the programmer. The process of catching and handling exceptions is known as exception handling.

In Python, exceptions are raised when an error occurs in a program. These errors can occur due to various reasons, such as invalid input, memory allocation issues, or network errors. Python provides a built-in mechanism to handle these exceptions.

The try-except block is used for exception handling in Python. The try block contains the code that might raise an exception. If an exception is raised, it is caught by the except block. The except block contains the code that handles the exception. If no exception is raised, the code in the except block is not executed.

Here is an example of exception handling in Python:

vros.py

try:
    # code that might raise an exception
except ExceptionType:
    # code to handle the exception
finally:
    # code that is always executed

In this example, the code in the try block is executed. If an exception is raised, the code in the except block is executed to handle the exception. The finally block is always executed, whether an exception is raised or not.

Exception handling is an important aspect of programming, as it helps to ensure that a program continues to run even when unexpected errors occur.

4. Explain different modes of opening a file.

In Python, when opening a file, you need to specify the mode in which the file is opened. The mode determines whether you can read, write or append to the file.

There are different modes in which a file can be opened:

Read mode ('r'): This is the default mode. In this mode, you can only read from the file, but you cannot modify it. If the file does not exist, an error will occur.
Write mode ('w'): In this mode, you can write to the file. If the file does not exist, it will be created. If the file already exists, its contents will be truncated (i.e., deleted) before you start writing to it.
Append mode ('a'): In this mode, you can write to the end of the file, without deleting its contents. If the file does not exist, it will be created.
Read and write mode ('r+'): In this mode, you can both read from and write to the file. If the file does not exist, an error will occur.
Write and read mode ('w+'): In this mode, you can both read from and write to the file. If the file does not exist, it will be created. If the file already exists, its contents will be truncated before you start writing to it.
Append and read mode ('a+'): In this mode, you can both read from and write to the end of the file, without deleting its contents. If the file does not exist, it will be created.

The syntax for opening a file in a specific mode is as follows:

vros.py

file_object = open('file_name', 'mode')

Here, file_name is the name of the file you want to open, and mode is the mode in which you want to open the file. After you finish working with the file, you should close it using the close() method.

vros.py

file_object.close()

It is a good practice to close the file after you have finished working with it, so that you can free up system resources.

5. Write the syntax of fopen() with example.

6. What are various modes of file object? Explain any five of them.

In Python, a file object can be opened in different modes to specify how the file should be opened or used. The various modes of file object in Python are:

"r" - Read Mode: This is the default mode of opening a file. It is used for reading the contents of a file. If the specified file does not exist, it will raise an error.

Syntax: file_object = open("filename", "r")

Example:

vros.py

file = open("example.txt", "r")
print(file.read())
file.close()

"w" - Write Mode: This mode is used for writing to a file. If the specified file does not exist, it will create a new file. If the file already exists, it will truncate the file to zero length.

Syntax: file_object = open("filename", "w")

Example:

vros.py

file = open("example.txt", "w")
file.write("This is some text.")
file.close()

"a" - Append Mode: This mode is used for appending to an existing file. If the specified file does not exist, it will create a new file.

Syntax: file_object = open("filename", "a")

Example:

vros.py

file = open("example.txt", "a")
file.write("This is some more text.")
file.close()

"x" - Exclusive Creation Mode: This mode is used to create a new file, but it raises an error if the file already exists.

Syntax: file_object = open("filename", "x")

Example:

vros.py

file = open("example.txt", "x")
file.write("This is some text.")
file.close()

"b" - Binary Mode: This mode is used to open a file in binary mode. It is used for non-text files like images, audio, and video files.

Syntax: file_object = open("filename", "b")

Example:

vros.py

file = open("example.jpg", "rb")
file_content = file.read()
file.close()

7. Explain exception handling with example using try, except, raise keywords.

Exception handling is a process in which the program can handle the errors or exceptions that occur during the execution of the program. Python provides a simple and powerful mechanism to handle exceptions using the try, except, and raise keywords.

The try block contains the code that might raise an exception, and the except block contains the code that handles the exception if it occurs.

Here's an example of using try, except, and raise to handle exceptions in Python:

vros.py

try:
    x = int(input("Enter a number: "))
    if x < 0:
        raise ValueError("The number cannot be negative.")
    else:
        print("The number is:", x)
except ValueError as ve:
    print("Error: ", ve)

In the above example, we take input from the user and check if it is a negative number or not. If it is negative, we raise a ValueError exception. The except block catches the exception and prints an error message.

If the user enters a non-negative number, the code in the else block is executed and the number is printed.

Note that in the except block, we are using the as keyword to assign the exception object to a variable ve. This allows us to access the error message and other details of the exception.

8. Explain try...except blocks for exception handling in Python.

In Python, the try...except block is used for exception handling. The try block contains the code that may raise an exception. If an exception is raised, it is caught by the except block, which handles the exception and prevents the program from crashing.

The basic syntax for try...except block in Python is as follows:

vros.py

try:
    # code that may raise an exception
except ExceptionType:
    # code to handle the exception

Here, the try block contains the code that may raise an exception. If an exception of type ExceptionType is raised, it is caught by the except block. The except block contains the code to handle the exception.

For example, consider the following code that attempts to divide two numbers and handles the ZeroDivisionError exception that may occur:

vros.py

try:
    num1 = int(input("Enter the first number: "))
    num2 = int(input("Enter the second number: "))
    result = num1 / num2
    print("Result:", result)
except ZeroDivisionError:
    print("Error: division by zero")

In this code, the try block contains the code to take two numbers from the user, perform the division operation, and print the result. If the user enters 0 as the second number, a ZeroDivisionError exception is raised. This exception is caught by the except block, which prints an error message indicating that division by zero is not possible.

Using try...except blocks in Python can help in handling errors and exceptions gracefully, and can prevent the program from crashing due to unexpected errors.

9. Explain various built in functions and methods.

In Python, built-in functions and methods are pre-defined functions that are available in the Python standard library. These functions and methods can be called from anywhere in the program without having to define them first. Here are some of the commonly used built-in functions and methods in Python:

print(): This function is used to display output on the console. It takes one or more arguments and prints them on the console. For example, print("Hello World") will print the text "Hello World" on the console.
len(): This function returns the length of a sequence, such as a string or a list. For example, len("Hello World") will return 11, which is the length of the string "Hello World".
range(): This function is used to generate a sequence of numbers. It takes one, two, or three arguments: start, stop, and step. For example, range(1, 6, 2) will generate the sequence 1, 3, and 5.
str(): This function converts any object to a string. For example, str(123) will convert the number 123 to the string "123".
int(): This function converts a string or a number to an integer. For example, int("123") will convert the string "123" to the integer 123.
append(): This method is used to add an element to the end of a list. For example, my_list.append("apple") will add the string "apple" to the end of the list my_list.
sort(): This method is used to sort a list in ascending order. For example, my_list.sort() will sort the elements in the list my_list in ascending order.
join(): This method is used to join a list of strings into a single string. For example, "-".join(["apple", "orange", "banana"]) will return the string "apple-orange-banana".
split(): This method is used to split a string into a list of substrings. It takes one argument, which is the separator. For example, "apple-orange-banana".split("-") will return the list ["apple", "orange", "banana"].
type(): This function returns the data type of a variable or an object. For example, type("Hello World") will return the data type "str".

10. Explain open() and close() methods for opening and closing a file.

In Python, open() and close() methods are used for opening and closing a file, respectively.

The open() method is used to open a file and return a file object. It takes two arguments: the path to the file and the mode in which the file should be opened. The path can be either an absolute path or a relative path. The mode specifies the purpose for which the file is being opened. Some common modes include:

'r': read mode, used for reading data from a file
'w': write mode, used for writing data to a file (overwrites the file if it already exists)
'a': append mode, used for appending data to a file (does not overwrite the file)

Here is an example of using the open() method to read a file:

vros.py

file = open('example.txt', 'r')
content = file.read()
print(content)
file.close()

In this example, the open() method is used to open a file named example.txt in read mode. The contents of the file are then read using the read() method and stored in the content variable. Finally, the close() method is called to close the file.

It's important to remember to always close a file after you're done using it, to prevent data loss or corruption. If you don't close a file, any changes you've made to the file may not be saved.

Here's an example of using the open() method to write to a file:

vros.py

file = open('example.txt', 'w')
file.write('This is a test.')
file.close()

In this example, the open() method is used to open a file named example.txt in write mode. The write() method is then used to write the string 'This is a test.' to the file. Finally, the close() method is called to close the file.

11. Explain any three methods associated with files in Python.

Here are three commonly used methods associated with files in Python:

open(): This method is used to open a file and return a file object. It takes two arguments: the path to the file and the mode in which the file should be opened (e.g. 'r' for read mode, 'w' for write mode). For example:
vros.py
```
file = open('example.txt', 'r')
```
read(): This method is used to read the contents of a file. It takes an optional argument that specifies how many characters to read (if not specified, it will read the entire file). For example:
vros.py
```
content = file.read()
```
write(): This method is used to write data to a file. It takes a string as an argument and writes it to the file. If the file does not exist, it will be created. If it does exist, the contents will be overwritten. For example:
vros.py
```
file.write('Hello, world!')
```

These are just a few examples of the many methods associated with files in Python. Other methods include close(), seek(), and tell(). It's important to remember to close files when you are done using them to prevent data loss or corruption.

12. List and explain any five exceptions in Python.

Here are five common exceptions in Python and their explanations:

SyntaxError: This exception is raised when there is a syntax error in the code, such as a missing or incorrect keyword or a mismatched parenthesis.
NameError: This exception is raised when a variable or function is referenced before it has been defined or when a variable or function name is misspelled.
TypeError: This exception is raised when there is a mismatch between the type of object that is expected and the type of object that is received, such as trying to add a string and an integer.
ValueError: This exception is raised when there is an error with the value of an argument or input, such as trying to convert a string to an integer when the string contains non-numeric characters.
FileNotFoundError: This exception is raised when a file is not found at the specified path.

These are just a few examples of the many exceptions that can be raised in Python. It's important to handle exceptions in your code to prevent your program from crashing and to provide helpful error messages to users.

13. List out keywords used in exception handling.

Here are the keywords used in exception handling in Python:

try: This keyword is used to start a try-except block. The code that is being monitored for exceptions is placed inside the try block.
except: This keyword is used to define the code that should be executed when an exception is raised. It is always followed by the type of exception that is being handled.
finally: This keyword is used to define a block of code that will be executed after the try and except blocks have finished executing, regardless of whether an exception was raised or not.
raise: This keyword is used to explicitly raise an exception.
assert: This keyword is used to verify that a condition is true, and raise an AssertionError if it is false.
else: This keyword is used to define a block of code that should be executed if no exceptions are raised.
with: This keyword is used to simplify the management of resources (such as files) by automatically closing them when they are no longer needed.

Note that some of these keywords (such as try, except, and finally) are specific to exception handling, while others (such as assert and with) have broader applications.

14. How python handles the exception? Explain with an example program.

Python handles exceptions using a try-except block. A try-except block is used to catch and handle exceptions that occur during the execution of a program. The try block contains the code that is being monitored for exceptions, and the except block contains the code that is executed when an exception is raised.

Here is an example program that demonstrates how Python handles exceptions:

vros.py

try:
    num1 = int(input("Enter a number: "))
    num2 = int(input("Enter another number: "))
    result = num1 / num2
    print("The result is:", result)
except ValueError:
    print("Invalid input! Please enter a valid number.")
except ZeroDivisionError:
    print("Cannot divide by zero!")
except Exception as e:
    print("An error occurred:", e)
finally:
    print("Execution complete.")

In this example, the program asks the user to input two numbers, then divides the first number by the second number and prints the result. However, the program is designed to handle exceptions that may occur during execution.

The try block contains the code that may raise an exception. In this case, it is the division operation. The except blocks contain the code that is executed when an exception of a specific type is raised. The first except block handles the ValueError that may occur if the user inputs an invalid number. The second except block handles the ZeroDivisionError that may occur if the user inputs a zero as the second number. The last except block handles any other type of exception that may occur, and prints the error message to the user.

Finally, the finally block is executed after the try and except blocks have completed, regardless of whether an exception was raised or not. In this case, the finally block simply prints a message to indicate that the program has completed execution.

Overall, the try-except block is a powerful tool in Python for handling exceptions and making your code more robust and reliable.

15. Differentiate between an error and exception.

ERROR

An error is a problem that occurs before the code is executed.
These can be syntax errors, such as missing or misplaced punctuation, or logical errors, such as referring to a variable that has not been defined.
These errors are detected by the Python interpreter when the code is compiled, and the program will not be executed until the errors are fixed.
Example of an error:

vros.py

print("Hello World)

In this code, there is a syntax error because the closing quotation mark is missing at the end of the string. This will raise a SyntaxError because the program cannot be executed until the error is fixed.

EXCEPTION

An exception is a problem that occurs during the execution of the code.
These can be caused by various factors, such as invalid user input or unexpected conditions that were not anticipated by the programmer.
When an exception occurs, the program stops executing at that point and raises an exception object, which can be handled by the program to avoid termination or provide additional information to the user.
Example of an exception:

vros.py

x = 5
y = 0
z = x/y

In this code, a ZeroDivisionError will occur because it is not possible to divide any number by zero. This is an exception because the program is executing properly up to this point, but it cannot continue because of the error. The exception can be handled using a try-except block to display an appropriate error message to the user.

16. How to create a user defined exception?

In Python, you can create a user-defined exception by creating a new class that inherits from the Exception class or one of its subclasses. Here is an example:

vros.py

class MyException(Exception):
    pass

In this example, we have defined a new exception class called MyException that inherits from the built-in Exception class. You can add any additional functionality to this class as needed.

To raise this exception in your code, you simply need to create an instance of the MyException class and raise it using the raise statement. Here is an example:

vros.py

def my_function():
    # Some code here
    if some_condition:
        raise MyException('An error occurred')
    # Some more code here

In this example, we have defined a function called my_function() that checks for a condition and raises the MyException exception if the condition is true. Note that when raising the exception, we pass a string message that describes the error.

17. Give the syntax and significance of input() method.

The input() function is a built-in function in Python that allows you to read a line of text input from the user. The syntax of the input() function is simple:

vros.py

input([prompt])

The prompt parameter is an optional string that is displayed to the user before the input is requested. If the prompt is not specified, the function will not display any message.

Here's an example of using the input() function to get user input:

vros.py

name = input("What is your name? ")
print("Hello, " + name + "!")

In this example, the input() function prompts the user with the message "What is your name?". The user can then type in their name, and the input() function will return that value as a string. The program then uses string concatenation to create a personalized greeting for the user.

The input() function is useful for creating interactive Python programs that require user input. It can be used to prompt the user for input in a variety of situations, such as asking for a password, a username, or any other type of text input.

18. Give syntax of the methods which can be used to take input from the user in Python program.

There are two main methods to take input from the user in Python:

Using the input() method:

Syntax:

vros.py

input([prompt])

Example:

vros.py

name = input("Enter your name: ")
print("Hello, " + name + "!")

Using command line arguments with the sys module:

Syntax:

vros.py

import sys
 
arg_value = sys.argv[index]

Example:

vros.py

import sys
 
name = sys.argv[1]
print("Hello, " + name + "!")

In the second method, the user needs to pass the input as a command line argument when running the program. The input can be accessed using the sys.argv list, where the first argument (sys.argv[0]) is the name of the script file and the subsequent arguments can be accessed using their index (sys.argv[1], sys.argv[2], etc.).

19. Write a Python program which will throw exception if the value entered by user is less than zero.

vros.py

try:
    num = int(input("Enter a number: "))
    if num < 0:
        raise ValueError("Number should be greater than or equal to zero")
    print("Number entered:", num)
except ValueError as ve:
    print("Error:", ve)

Explanation:

The program prompts the user to enter a number using input() function.
It then converts the user input to an integer using int() function.
If the user enters a number less than zero, it raises a ValueError exception with a custom error message.
The try block is used to catch any exception that might occur while executing the code in the block.
The except block catches the ValueError exception raised in the try block and prints a custom error message.

Sample Output:

vros.py

Enter a number: -5
Error: Number should be greater than or equal to zero

If the user enters a non-negative number, the program will print the number entered.

20. Write a Python program to accept an integer number and use try/except to catch the exception if a floating point number is entered.

vros.py

while True:
    try:
        num = int(input("Enter an integer number: "))
        print("You entered:", num)
        break
    except ValueError:
        print("Invalid input. Please enter an integer.")

In this program, we use a while loop to continuously ask the user to enter an integer until a valid input is received. The try block attempts to convert the user input to an integer using the int() function. If the input is a valid integer, the program prints the number and breaks out of the loop. If the input is not a valid integer (e.g., a floating-point number), a ValueError exception is raised, and the program prints an error message prompting the user to enter a valid integer. The except block catches this exception and continues the loop until a valid input is received.

21. Write a Python program to read contents of ‘first.txt’ file and write same content in second.txt file.

vros.py

try:
    # Open the first file for reading
    with open('first.txt', 'r') as file1:
        # Read the contents of the file
        contents = file1.read()
 
    # Open the second file for writing
    with open('second.txt', 'w') as file2:
        # Write the contents to the second file
        file2.write(contents)
 
    # Print a message to indicate that the operation was successful
    print('File contents copied successfully!')
 
except FileNotFoundError:
    print('One or both of the files do not exist!')

In this program, we use a try-except block to catch the FileNotFoundError that might occur if the "first.txt" file is not found. Within the try block, we first open the "first.txt" file in read mode and read its contents using the read() method. Then, we open the "second.txt" file in write mode and write the contents using the write() method. Finally, we print a message to indicate that the operation was successful.

22. Write a Python program to append data to an existing file 'python.py'. Read data to be appended from the use. Then display the contents of entire file.

vros.py

# open file in append mode
with open('python.py', 'a') as f:
    # get data to append from user
    data = input("Enter data to append: ")
    # write data to file
    f.write(data)
 
# open file in read mode
with open('python.py', 'r') as f:
    # read and display contents of entire file
    contents = f.read()
    print(contents)

In this program, we first open the file 'python.py' in append mode using the open() function with the mode 'a'. Then we get the data to append from the user using the input() function and write it to the file using the write() method of the file object.

Next, we open the file again, but this time in read mode using the open() function with the mode 'r'. We then read the contents of the entire file using the read() method of the file object and store it in the contents variable. Finally, we print the contents of the file using the print() function.

23. Write a Python program to read a text file and print number of lines, words and characters.

vros.py

# Open the file in read mode
with open('myfile.txt', 'r') as file:
    # Initialize variables
    lines = 0
    words = 0
    characters = 0
 
    # Read the contents of the file line by line
    for line in file:
        # Count the number of lines
        lines += 1
 
        # Split the line into words
        words_list = line.split()
 
        # Count the number of words
        words += len(words_list)
 
        # Count the number of characters
        characters += len(line)
 
# Print the results
print(f'Number of lines: {lines}')
print(f'Number of words: {words}')
print(f'Number of characters: {characters}')

In this program, we first open the file using the open() function and initialize variables to count the number of lines, words, and characters. We then use a for oop to read the contents of the file line by line. For each line, we increment the lines variable, split the line into words using the split() method, and increment the words variable by the number of words in the line. We also increment the characters variable by the length of the line. Finally, we print the results using f-strings. Note that we use the with statement to ensure that the file is automatically closed after we are done with it.

24. Describe the term file I/O handling in detail.

File I/O (Input/Output) handling refers to the process of reading data from and writing data to files in a computer's file system using the Python programming language. In Python, there are two types of files that can be handled:

Text files: These are files that contain printable characters and are usually used to store textual data, such as plain text documents or source code files.
Binary files: These are files that contain non-printable characters and are used to store non-textual data, such as images, audio files, or executables.

Python provides built-in functions and modules to perform various file I/O operations, such as opening, reading, writing, and closing files. The general workflow for handling files in Python is as follows:

Open the file: The first step in file I/O handling is to open the file using the open() function. This function takes two arguments - the file name and the mode in which the file will be opened (read, write, append, etc.). If the file is successfully opened, a file object is returned, which can be used to perform file operations.
Read or write data: Once the file is opened, you can read or write data to/from the file using the methods of the file object. For example, you can use the read() method to read the contents of a file, or the write() method to write data to a file.
Close the file: Once you are done with the file, you should close it using the close() method. This ensures that any changes made to the file are saved and any resources used by the file are released.

Here's an example of reading the contents of a text file using Python:

vros.py

# Open the file in read mode
file = open('myfile.txt', 'r')
 
# Read the contents of the file
contents = file.read()
 
# Close the file
file.close()
 
# Print the contents of the file
print(contents)

And here's an example of writing data to a file:

vros.py

# Open the file in write mode
file = open('myfile.txt', 'w')
 
# Write data to the file
file.write('Hello, world!')
 
# Close the file
file.close()

Unit 5