python-debug-execution

# Python Debug Execution Pattern When executing Python scripts that may fail, use this pattern to surface clear error information and diagnose issues effectively. ## Core Technique ### 1. Execute with Full Error Output Always run Python scripts with stderr redirected to stdout and echo the exit code: ```bash python3 script.py 2>&1 ; echo Exit code: $? ``` **Why this works:** - `2>&1` captures both stdout and stderr, ensuring tracebacks are visible - `echo Exit code: $?` reveals the actual exit status for debugging - Avoids opaque "command failed" errors that hide the real cause ### 2. Verify Working Directory in Script Before any file operations in Python scripts, add working directory verification: ```python import os # At the start of your script or before file operations print(f"Current working directory: {os.getcwd()}") # For debugging, also list directory contents print(f"Directory contents: {os.listdir('.')}") ``` **Why this works:** - File not found errors often stem from incorrect working directory assumptions - Makes path-related failures immediately diagnosable - Confirms the execution context matches expectations ## Complete Debugging Workflow ### Step 1: Add Diagnostic Code to Script ```python #!/usr/bin/env python3 import os import sys def main(): # Diagnostic: verify execution context print(f"Working directory: {os.getcwd()}") print(f"Python version: {sys.version}") print(f"Directory listing: {os.listdir('.')}") # Your actual logic here # ... if __name__ == "__main__": main() ``` ### Step 2: Execute with Full Error Capture ```bash python3 script.py 2>&1 ; echo Exit code: $? ``` ### Step 3: Analyze Output Look for: - Traceback messages (indicate code errors) - Exit code (0 = success, non-zero = failure) - Working directory confirmation - Missing file/directory errors ## Common Failure Patterns | Symptom | Likely Cause | Debug Clue | |---------|-------------|------------| | FileNotFoundError | Wrong working directory | Check `os.getcwd()` output | | ModuleNotFoundError | Missing dependencies | Traceback shows import path | | PermissionError | File access issues | Traceback shows file path | | Silent failure (exit 0, no output) | Logic bug, not crash | Add print statements | ## When to Use This Pattern - Running Python scripts in automated/agent contexts - Debugging scripts that interact with files - Troubleshooting CI/CD pipeline failures - Any scenario where script output may be truncated or hidden