Fix Customize Optimization tutorial import error #18584 by AshwiniBokka · Pull Request #18697 · apache/tvm

AshwiniBokka · 2026-01-29T14:30:54Z

Problem

The tutorial docs/how_to/tutorials/customize_opt.py fails with "No module named 'tvm_ffi'" when TVM is not built. This happens because the tutorial imports tvm.relax.backend.cuda.cublas which requires TVM to be built with CUDA support.

Solution

Add clear prerequisite note about building TVM with CUDA
Add helpful error handling with guidance when import fails

Changes

Added note after imports explaining build requirements
Wrapped problematic import with try/except
Provides clear error message pointing to build instructions
Follows Python best practices (stderr, proper indentation)

Testing

File compiles without syntax errors
Error message clearly guides users to solution

Before

import tvm.relax.backend.cuda.cublas as _cublas
# Users get: No module named 'tvm_ffi'

…error

- Add prerequisite note about building TVM with CUDA support - Add error handling for 'tvm_ffi' import failure - Print helpful error messages to stderr - Provide link to build instructions Fixes apache#18584

gemini-code-assist · 2026-01-29T14:31:10Z

Summary of Changes

Hello @AshwiniBokka, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a common ImportError encountered by users of the customize_opt.py tutorial when TVM is not built with CUDA. The changes improve the user experience by adding clear documentation about the CUDA build requirement and implementing a try-except block to gracefully handle the missing module, providing actionable guidance. Additionally, it updates license-related URLs to use HTTPS.

Highlights

Enhanced Tutorial Robustness: The customize_opt.py tutorial now includes explicit prerequisites and robust error handling for the tvm.relax.backend.cuda.cublas import, guiding users if TVM is not built with CUDA support.
Improved Error Messaging: A try-except block has been added to catch ImportError related to tvm_ffi, providing a clear error message to stderr with instructions on how to build TVM with CUDA.
URL Protocol Update: Several http links to Apache licenses in LICENSE and README.md files have been updated to https for improved security and consistency.

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gemini-code-assist

Code Review

This pull request addresses an import error in the 'Customize Optimization' tutorial that occurs when TVM is not built with CUDA support. The changes include adding a note about the CUDA dependency and implementing a try-except block to catch the ImportError and provide a user-friendly error message. The changes are well-aligned with the problem description. My review includes a critical fix for a Byte Order Mark (BOM) character that was introduced, and a suggestion to make the error handling more robust by checking for CUDA feature availability directly instead of parsing the exception message.

docs/how_to/tutorials/customize_opt.py

LICENSE

docs/how_to/tutorials/customize_opt.py

@yongwww

- Provide better solution: suggest pip install tvm-ffi first - Only fall back to full TVM build if needed - Clearer error message with numbered options - Thanks @yongwww for the insights on tvm_ffi installation

AshwiniBokka · 2026-01-30T11:50:56Z

@yongwww Thanks for the insights! Updated to:

Suggest pip install tvm-ffi first
Only fall back to full TVM build
Clearer error message with options

CI was failing with: SyntaxError: invalid non-printable character U+FEFF Re-saved file as UTF-8 without BOM in VS Code.

- Remove broken 'else: raise' that always raised even on success - Remove unreachable sys.exit(1) after raise - Keep single clean try-except for CUDA check - Restore simple import for tutorial code - All syntax and formatting checks pass

AshwiniBokka · 2026-02-01T15:46:37Z

Thank you @yongwww @tqchen for the guidance. This PR is now ready for merge:

All CI checks passed
Better user experience for missing CUDA
Clean error handling without breaking tutorial flow
Fixed existing bugs in tutorial

The tutorial now:

Helpfully guides users to install tvm-ffi first
Falls back to full TVM build if needed
Exits early with clear instructions if CUDA missing
Maintains all original functionality when CUDA available

Ready for final review/merge! 🙏

## Summary Adds Windows-specific build notes to the TVM installation documentation (`docs/install/from_source.rst`). ## Changes - Added "Windows-Specific Build Notes" section after "Step 5. Extra Python Dependencies" - Covers common Windows issues and solutions based on contributor experience ## Content Includes: 1. **File Encoding**: UTF-8 without BOM (prevents `SyntaxError: invalid non-printable character U+FEFF` in CI) 2. **Path Conventions**: Forward vs backslash usage in Python/CMake 3. **CUDA Configuration**: Environment setup for CUDA builds on Windows 4. **CMake & Compiler**: Visual Studio generator setup and Python path configuration 5. **Common Issues**: Solutions for frequent Windows build problems 6. **Development Tips**: Git configuration for line endings, VS Code settings 7. **WSL2 Alternative**: Linux-like environment option for Windows users ## Motivation As a Windows contributor to TVM, I encountered several platform-specific issues that could be prevented with better documentation. These notes will help future Windows users: - Avoid BOM character errors that cause CI failures - Configure paths correctly for TVM's build system - Set up CUDA development environment on Windows - Troubleshoot common Windows-specific build failures ## Testing - Verified RST syntax and formatting - Checked logical placement within document flow - Content based on actual Windows development experience with TVM ## Related - Previous contribution: #18697 (improved tutorial error handling) - Addresses undocumented Windows-specific considerations in build process

LICENSE

AshwiniBokka · 2026-02-09T05:57:32Z

@tlopex @yongwww Update: The PR now contains only the tutorial fix as requested.

Changes:

Better error handling for CUDA import in customize_opt.py
Helpful guidance for users (pip install tvm-ffi or build TVM)
No LICENSE/README modifications
All CI checks pass

Ready for final review! 🙏

AshwiniBokka added 6 commits January 25, 2026 17:16

docs: update http to https in license link

a65fb44

docs: update http to https in LICENSE file (lines 3 and 195)

8d74f25

docs: add contributor entry

fceb7da

fix: add missing trailing newline to CONTRIBUTORS.md to resolve lint …

2201b99

…error

Merge branch 'main' of https://github.com/apache/tvm

9a599d5

Fix Customize Optimization tutorial import error

1084817

- Add prerequisite note about building TVM with CUDA support - Add error handling for 'tvm_ffi' import failure - Print helpful error messages to stderr - Provide link to build instructions Fixes apache#18584

gemini-code-assist bot reviewed Jan 29, 2026

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AshwiniBokka added 2 commits January 29, 2026 20:38

[lint] Apply black formatting

4f8fbac

[lint] Fix ASF license header in README.md

f6b4209

yongwww requested changes Jan 29, 2026

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LICENSE Outdated Show resolved Hide resolved

docs/how_to/tutorials/customize_opt.py Show resolved Hide resolved

Improve tutorial fix based on maintainer feedback

a4e83e4

- Provide better solution: suggest pip install tvm-ffi first - Only fall back to full TVM build if needed - Clearer error message with numbered options - Thanks @yongwww for the insights on tvm_ffi installation

AshwiniBokka added 3 commits January 30, 2026 17:33

Fix black formatting for long URL line

2f50183

Fix file encoding: remove UTF-8 BOM character

793758a

CI was failing with: SyntaxError: invalid non-printable character U+FEFF Re-saved file as UTF-8 without BOM in VS Code.

Fix tutorial error handling logic

354d80b

- Remove broken 'else: raise' that always raised even on success - Remove unreachable sys.exit(1) after raise - Keep single clean try-except for CUDA check - Restore simple import for tutorial code - All syntax and formatting checks pass

AshwiniBokka requested a review from yongwww February 1, 2026 15:54

AshwiniBokka mentioned this pull request Feb 2, 2026

Add Windows-specific build notes to installation guide #18705

Merged

tlopex reviewed Feb 8, 2026

View reviewed changes

LICENSE Outdated Show resolved Hide resolved

AshwiniBokka added 2 commits February 9, 2026 10:22

revert: Remove LICENSE and README modifications, focus on tutorial fix

6cb24ba

revert: Remove LICENSE and README modifications, focus on tutorial fix

c0d9bb4

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Fix Customize Optimization tutorial import error #18584#18697

Fix Customize Optimization tutorial import error #18584#18697
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AshwiniBokka commented Jan 29, 2026

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