Module 12 Study Guide – Introduction to Python

Key Terms

Exception: An error that occurs during program execution (as opposed to syntax errors which are caught before running).

Traceback: Python's error report showing the chain of calls that led to the error, the file, line number, and error type.

try/except: A construct that catches exceptions and runs alternative code instead of crashing.

raise: A keyword to manually trigger an exception.

Debugging: The process of finding and fixing errors (bugs) in your code.

Print debugging: Adding print statements to trace variable values and program flow.

Lesson 1: Common Python Errors

SyntaxError: Grammar mistake - missing colon, parenthesis, quote
NameError: Undefined name - typo, undefined variable, missing import
TypeError: Wrong type - "hello" + 5, wrong number of arguments
ValueError: Wrong value - int("hello"), unpacking mismatch
IndexError: List index out of range
KeyError: Dictionary key not found (use .get() to avoid)
Always read error messages from the bottom up

Lesson 2: try/except/finally

Execution Order

try:       # 1. Try this code first
except:    # 2a. Runs if error occurs (skips else)
else:      # 2b. Runs if NO error (skips except)
finally:   # 3. ALWAYS runs

What to Know

Always catch specific exceptions, not bare except:
Use as e to capture the error message
else runs only when no exception occurred
finally always runs - good for cleanup
raise creates your own exceptions
Combine try/except with while loops for input validation

Lesson 3: Debugging Strategies

Read the traceback: Line number, error type, error message
Print debugging: Add print() to trace variable values
Comment out code: Isolate the problematic section
Rubber duck debugging: Explain code line by line out loud
Common mistakes: = vs ==, indentation, off-by-one, modifying list while looping
Take breaks: Fresh eyes often spot bugs faster

Lesson 4: Next Steps

OOP: Classes and objects - the natural next topic after this course
Web development: Flask (lightweight) or Django (full-featured)
Data science: pandas, NumPy, matplotlib
Automation: File organization, web scraping, report generation
Best advice: Code every day, build projects, join communities

Review Questions

1. What is the difference between a SyntaxError and a NameError?

2. In what order do try/except/else/finally blocks execute?

3. Why should you catch specific exceptions instead of using bare except?

4. What is rubber duck debugging and why does it work?

5. How do you use the raise keyword?

6. What are three common beginner mistakes in Python?

Common Mistakes to Avoid

Using bare except: which catches all errors including ones you want to see
Ignoring error messages instead of reading them carefully
Not using try/except for user input that could fail
Putting too much code in the try block (makes it hard to know what failed)
Not testing edge cases (empty lists, zero values, missing files)
Forgetting that = is assignment and == is comparison

Module 12: Study Guide