Investigate unclear errors in Python PDF generation by displaying output immediately and inspecting error details. Use the resulting traceback, a record of where execution failed, to identify missing dependencies, font problems, or invalid file paths.
Debug Python PDF generation errors by using unbuffered output and stderr inspection to reveal actual tracebacks
Review the instructions the agent will receive before you install.
When Python PDF libraries (reportlab, fpdf, etc.) fail with generic "unknown error" messages, the actual cause is often hidden due to output buffering or error swallowing. This skill provides a technique to expose the real traceback.
Run the Python script with the -u flag (unbuffered output) and pipe stderr through head to capture the actual error:
python -u your_script.py 2>&1 | head -100
Or more specifically, to focus on stderr:
python -u your_script.py 2>&1 | head -50
-u flag: Forces Python to run in unbuffered mode, ensuring output (including errors) is flushed immediately rather than held in buffers that may be lost on crash2>&1: Redirects stderr to stdout so both streams are captured togetherhead: Limits output to show the most relevant error messages at the topLocate the Python script that generates the PDF and is producing generic errors.
python -u generate_pdf.py 2>&1 | head -100
Look for:
Address the specific error revealed in the traceback.
Once fixed, run the script without the debug flags to confirm it works:
python generate_pdf.py
| Symptom | Likely Cause |
|---|---|
| "unknown error" on PDF save | File path doesn't exist or no write permissions |
| Generic failure during build | Missing font files or font registration issues |
| Silent crash | ImportError for missing dependencies |
| Incomplete PDF | Script terminated early due to unhandled exception |
If the above doesn't work, try:
# Capture full stderr to a file
python -u script.py 2> error.log
# Use Python's traceback module explicitly
python -c "import traceback; exec(open('script.py').read())" 2>&1
# Run with verbose import tracing
python -v -u script.py 2>&1 | head -200
# Before: Generic error
python create_checklist.py
# Output: "Error: unknown"
# After: Actual traceback
python -u create_checklist.py 2>&1 | head -50
# Output: "FileNotFoundError: [Errno 2] No such file or directory: '/fonts/Helvetica.ttf'"
-u flag is available in Python 2.7+ and all Python 3 versionsheadNo reviews yet. Tell others what you thought.
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