How is debugging of a Python program carried out?

Debugging in Python is performed at several levels:

1. Syntax and logical error checking:

   • Using static analyzers (flake8, Pylint) to identify syntax errors, style violations, and potential issues.
   • Running tests (unittest, pytest) to verify the correctness of logic and behavior of different parts of the program.

2. Using print to output intermediate values:

   • A simple but effective way to display variable values and understand the flow of the program.

   # Example of using print for debugging
   def my_function(data):
       print(f"Received data: {data}")  # Output input data
       result = data * 2
       print(f"Intermediate result: {result}") # Output intermediate result
       return result
   
   my_function(10)
   

3. Built-in debugger pdb:

   • Provides an interactive environment for step-by-step execution, setting breakpoints, viewing variable values, call stack, etc.
   • Can be run from the command line or embedded in code.

   import pdb
   
   def my_function(data):
       pdb.set_trace()  # Breakpoint
       result = data * 2
       return result
   
   my_function(10)
   

4. Integrated Development Environments (IDEs) with debuggers:

   • VS Code, PyCharm, Sublime Text, Spyder, and other IDEs offer more convenient and powerful debugging tools with a graphical interface:
     • Setting and managing breakpoints.
     • Step over, step into, step out.
     • Viewing variable values in the current scope.
     • Evaluating arbitrary expressions.
     • Viewing call stack.
     • Changing variable values on the fly.

5. Logging:

   • Using the logging module to record information about program execution, errors, and warnings to files or console. Allows tracking program behavior in real conditions without stopping execution.

   import logging
   
   logging.basicConfig(level=logging.INFO, format='%(asctime)s - %(levelname)s - %(message)s')
   
   def process_data(data):
       logging.info(f"Processing data: {data}")
       if data < 0:
           logging.warning("Negative data received.")
       # ... processing logic ...
   
   process_data(5)
   process_data(-2)
   

The choice of debugging method depends on the complexity of the problem, the development stage, and personal preferences. Combining these approaches is the most effective.