python-debug-execution-911f17

# Python Debug Execution This skill provides a pattern for debugging Python script execution failures. It ensures you capture actual tracebacks instead of opaque errors and verifies the working directory before file operations. ## Core Pattern ### 1. Execute with Full Traceback Capture Always run Python scripts with stderr redirected and exit code reported: ```bash python3 script.py 2>&1 ; echo Exit code: $? ``` This pattern: - `2>&1` - Redirects stderr to stdout so all output (including tracebacks) is captured together - `echo Exit code: $?` - Reports the exit code to distinguish between successful runs and failures **Why this matters:** Opaque errors without tracebacks make it impossible to identify the root cause. The exit code tells you if the script succeeded (0) or failed (non-zero). ### 2. Verify Working Directory Before File Operations Before any file read/write operations in your Python script, add: ```python import os print(f"Current working directory: {os.getcwd()}") ``` Or for debugging, add at the start of your script: ```python import os import sys # Debug: show execution context print(f"Script path: {__file__}") print(f"Working directory: {os.getcwd()}") print(f"Python version: {sys.version}") ``` **Why this matters:** File operations often fail due to incorrect assumptions about the current working directory. Verifying `os.getcwd()` helps diagnose path-related errors. ## Usage Examples ### Example 1: Running a Script with Debug Output ```bash # Instead of: python3 analyze.py # Use: python3 analyze.py 2>&1 ; echo Exit code: $? ``` ### Example 2: Script with Directory Verification ```python #!/usr/bin/env python3 import os import pandas as pd # Verify execution context print(f"Working directory: {os.getcwd()}") # Now safe to do file operations data_path = "data/input.csv" print(f"Attempting to read: {data_path}") # Check if file exists before reading if os.path.exists(data_path): df = pd.read_csv(data_path) print(f"Successfully loaded {len(df)} rows") else: print(f"ERROR: File not found at {os.path.abspath(data_path)}") print(f"Directory contents: {os.listdir('.')}") ``` ### Example 3: Debug-First Script Template ```python #!/usr/bin/env python3 """Template for debuggable Python scripts.""" import os import sys import traceback def main(): # Debug: execution context print("=" * 50) print(f"Script: {__file__}") print(f"Working directory: {os.getcwd()}") print(f"Python: {sys.version}") print("=" * 50) try: # Your main logic here pass except Exception as e: print(f"ERROR: {type(e).__name__}: {e}") traceback.print_exc() sys.exit(1) if __name__ == "__main__": main() ``` ## Troubleshooting Checklist When a Python script fails: 1. **Check the exit code** - Non-zero means failure 2. **Read the full traceback** - Look for the actual error message and line number 3. **Verify working directory** - Use `os.getcwd()` to confirm file paths are correct 4. **Check file existence** - Use `os.path.exists()` before operations 5. **Use absolute paths** - Consider `os.path.abspath()` for clarity ## When to Apply This Pattern - Running any Python script from the command line - Debugging script execution failures in automated agents - Writing scripts that perform file I/O operations - Creating reproducible execution environments