Bioinfo Lab

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Important

Please create a new PPT file, document every subsequent step you take with screenshots, save it as a PDF upon completion of all steps, and submit it to the “Weekly Report Assignment”.

This is an important part of your “General Performance”. Please ensure timely submission!!!

Recommended: 3, 5, 6, 7, 9, 10, 12, 14, 15, 16

Tips

tab type the first few letters of a file name or command, then press the Tab key. Linux will automatically complete the rest for you.
history You can see all the commands you have run before.
In Python interactive mode, use help() or ? to view documentation for errors and exceptions.
Try ai, aiw, and aid for AI assistance.

1. Log into the remote Linux Server

Linux Server:

IP: click

Port: 13579

User Name: dt + Student ID (e.g. dt2023000001)

Password: dt + Student ID + @biuh2025 (e.g. dt2023000001@biuh2025)

2. Create Practice Directory and Files

cd ~
mkdir w10_error_handling
cd w10_error_handling

3. Common Python Errors Practice

Create a script to demonstrate the five most common errors:

nano common_errors.py

Type the following code:

# 1. SyntaxError
# while True

# 2. NameError
# print(new_variable)

# 3. TypeError
# 1+'a'

# 4. FileNotFoundError
# fi=open('okokokokok.txt','r')

# 5. IndentationError
# while True:
# print('yes')

# Uncomment each line one by one to see the errors
print("Step 1: Uncomment the SyntaxError line")

Save: Ctrl + O Exit: Ctrl + X

Run the script:

python3 common_errors.py

4. Understanding Error Messages

Create a script to generate a NameError and analyze the traceback:

nano traceback_demo.py

Type the following code:

print(undefined_var)

Save and exit, then run:

python3 traceback_demo.py

You will see:

Traceback (most recent call last):
  File "traceback_demo.py", line 1, in <module>
    print(undefined_var)
NameError: name 'undefined_var' is not defined

Error breakdown:

Traceback: Error roadmap showing the call stack
File “traceback_demo.py”: Location of the error
line 1: Exact line number
NameError: Error type
name ‘undefined_var’ is not defined: Specific error message

5. Basic Exception Handling

Create a script with try-except structure:

nano basic_try_except.py

Type the following code:

try:
    # Code that might fail
    result = 10 / 0
except ZeroDivisionError:
    print("Oops! Can't divide by zero!")

Save and run:

python3 basic_try_except.py

Expected output: Oops! Can't divide by zero!

6. BMI Calculator with Error Handling

Create a practical BMI calculator:

nano bmi_calculator.py

Type the following code:

try:
    weight = float(input("Enter weight (kg): "))
    height = float(input("Enter height (m): "))
    bmi = weight / height
except ZeroDivisionError:
    print("Alert! Did you enter height as zero?")
except ValueError:
    print("Please enter valid numbers!")

Save and run:

python3 bmi_calculator.py

Test with height = 0 to trigger ZeroDivisionError.

7. File Handling with Exception Handling

Create a file detective script:

nano file_detective.py

Type the following code:

try:
    with open("ghost_file.txt") as f:
        print(f.read())
except FileNotFoundError:
    print("Pssst... this file doesn't exist!")

Save and run:

python3 file_detective.py

Expected output: Pssst... this file doesn't exist!

8. Catch-All Exception Handler

Create a script to catch any unexpected error:

nano catch_all.py

Type the following code:

try:
    magic_number = "100" + 5
except Exception as e:
    print("Error details:", e)

Save and run:

python3 catch_all.py

Expected output shows the TypeError details.

9. User-Friendly Error Messages

Create an age input validator:

nano friendly_errors.py

Type the following code:

try:
    user_age = int(input("Enter age: "))
except ValueError:
    print("Hey! Numbers only please :)")

Save and run:

python3 friendly_errors.py

Test with non-numeric input.

10. Handling Multiple Exception Types

Create a script with multiple except blocks:

nano multiple_exceptions.py

Type the following code:

try:
    age = int(input("Age: "))
    print(str(100/age))
except ValueError:
    print("Numbers only!")  
except ZeroDivisionError:
    print("Age can't be zero!") 

Save and run:

python3 multiple_exceptions.py

Test with:

Input 0 → ZeroDivisionError
Input string → ValueError
Input 4 → Successful division

11. Tuple-Style Exception Catching

Create a script catching multiple exceptions together:

nano tuple_catch.py

Type the following code:

try:
    with open("grades.txt") as f:
        print(f.read())
except (FileNotFoundError, PermissionError):
    print("File problem! Check if:")
    print("- File exists")
    print("- You have access")

Save and run:

python3 tuple_catch.py

12. Grade Calculator Exercise

Create a grade calculator:

nano grade_calculator.py

Type the following code:

try:
    total = float(input("Total points: "))
    earned = float(input("Earned points: "))
    percentage = (earned/total)*100
    print(f"Percentage: {percentage}%")
except ValueError:
    print("Numbers only!")
except ZeroDivisionError:
    print("Total can't be zero!")

Question: Modify this to use tuple-style catching.

13. Pet Age Calculator

Create a pet age calculator:

nano pet_age.py

Type the following code:

try:
    human_years = int(input("Dog's age: "))
    dog_years = human_years * 7
    print(f"Dog age: {dog_years}")
except ValueError:
    print("Enter whole number!")
except Exception:
    print("Something unexpected happened!")

Question: Change it into tuple-style. Do we really need to do that?

14. The `finally` Clause

Create a script demonstrating finally:

nano finally_demo.py

Type the following code:

try:
    file = open("diary.txt", "r")
    print(file.read())
except FileNotFoundError:
    print("Diary not found!")
finally:
    print("This always runs - cleanup completed")

Save and run:

python3 finally_demo.py

The finally block executes regardless of whether an exception occurs.

15. The `else` Clause

Create a script demonstrating else:

nano else_demo.py

Type the following code:

try:
    num = float(input("Enter a number: "))
    result = 10 / num
except ZeroDivisionError:
    print("Can't divide by zero!")
else:
    print(f"Result is {result}")  # Only runs if no exception

Save and run:

python3 else_demo.py

The else block runs only when the try block succeeds.

16. Complete Exception Handling Pattern

Create a safe config loader:

nano safe_config.py

Type the following code:

config_file = False
try:
    config_file = open("game_config.cfg")
except FileNotFoundError:
    print("⚠ Config file missing!")
else:
    settings = config_file.read()
    print("Game configuration loaded!")
finally:
    if config_file:
        config_file.close()
    print("Resource cleanup completed")

Save and run:

python3 safe_config.py

17. Safe Divide Function

Create a function with complete exception handling:

nano safe_divide.py

Type the following code:

def safe_divide(a, b):
    try:
        result = a / b
    except ZeroDivisionError:
        print("Division by zero!")
    else:
        print(f"Result is {result}")
    finally:
        print("Operation complete")

safe_divide(10, 2)
safe_divide(5, 0)

Save and run:

python3 safe_divide.py

18. Network Request Error Handling

Create a network request handler (requires internet):

nano network_request.py

Type the following code:

import requests
try:
    response = requests.get("https://www.baidu.com", timeout=3)
    print("Connection successful!")
except requests.exceptions.ConnectTimeout:
    print("Oops! Connection took too long!")

Save and run:

python3 network_request.py

19. Retry Mechanism with Dynamic Wait Time

Create a retry script:

nano retry_dynamic.py

Type the following code:

import time,requests

wait_times = [3, 2, 1]  # Dynamic wait times

for attempt in range(3):
    try:
        requests.get("https://www.baidu.com",timeout=3)
        print(f"Attempt {attempt+1} succeeded!")
        break
    except Exception:
        print(f"Attempt {attempt+1} failed")
        time.sleep(wait_times[attempt])

Question: How can we dynamically change the wait-time? First time: 3s, Second time: 2s, Third time: 1s

20. Username Validation with Custom Exception

Create a username checker:

nano username_check.py

Type the following code:

existing_users = ["alice", "bob", "charlie"]

try:
    new_user = input("Choose username: ")
    if new_user in existing_users:
        raise ValueError("Username taken!")
    print("Username available!")
except ValueError as e:
    print(e)

Question: How can we use while-loop to add multiple users?

21. Password Strength Checker

Create a password validator using raise:

nano password_check.py

Type the following code:

def check_password(pwd):
    if len(pwd) < 8:
        raise Exception("Password too short!")
    if not any(c.isdigit() for c in pwd):
        raise Exception("Add numbers!")

try:
    check_password("weak")
except Exception as e:
    print("Weak password: " + str(e))

Save and run:

python3 password_check.py

22. Fahrenheit to Celsius Converter

Create a temperature converter:

nano fahrenheit_celsius.py

Type the following code:

try:
    fahr = float(input("Enter Fahrenheit: "))
except ValueError:
    print("Numbers only please!")
else:
    celsius = (fahr - 32) * 5/9
    print(f"{fahr}F = {celsius:.1f}C")

Question: Create a Celsius to Fahrenheit converter.

23. Temperature Range Validation

Create a temperature range checker:

nano temp_range.py

Type the following code:

try:
    temp = float(input("Enter temp (-100 to 212F): "))
    if not (-100 <= temp <= 212):
        raise ValueError("Unrealistic temperature!")
    print("Temperature accepted!")
except ValueError as e:
    print(f"Invalid input: {e}")

Question: Put “Range Check” into the “Fahrenheit-to-Celsius” converter.

End

Loading......

Password

Important

Recommended: 3, 5, 6, 7, 9, 10, 12, 14, 15, 16

Tips

1. Log into the remote Linux Server

2. Create Practice Directory and Files

3. Common Python Errors Practice

4. Understanding Error Messages

5. Basic Exception Handling

6. BMI Calculator with Error Handling

7. File Handling with Exception Handling

8. Catch-All Exception Handler

9. User-Friendly Error Messages

10. Handling Multiple Exception Types

11. Tuple-Style Exception Catching

12. Grade Calculator Exercise

13. Pet Age Calculator

14. The finally Clause

15. The else Clause

16. Complete Exception Handling Pattern

17. Safe Divide Function

18. Network Request Error Handling

19. Retry Mechanism with Dynamic Wait Time

20. Username Validation with Custom Exception

21. Password Strength Checker

22. Fahrenheit to Celsius Converter

23. Temperature Range Validation

14. The `finally` Clause

15. The `else` Clause