Add advanced Python client examples

[1bcMax]

Summary

Adds 5 advanced Python client examples demonstrating x402 SDK v2 features.

Part of #841 - addresses TODO item: "Add advanced/custom Python client examples"

Examples

Example	Description
hooks.py	Payment lifecycle hooks (before, after, failure callbacks)
preferred_network.py	Custom network preference selector
builder_pattern.py	Network-specific registration with wildcards
error_recovery.py	Error classification and recovery strategies
custom_transport.py	Custom httpx transport with retry/timing

Features

• CLI entry point (index.py) for running examples
• Comprehensive test suite (40 unit tests passing)
• E2E integration tests
• README documentation

Test Results

============================= test session starts ==============================
collected 40 items

tests/test_builder_pattern.py ........                                   [ 20%]
tests/test_custom_transport.py .........                                 [ 42%]
tests/test_error_recovery.py ...........                                 [ 72%]
tests/test_hooks.py .......                                              [ 90%]
tests/test_preferred_network.py ....                                     [100%]

============================== 40 passed in 0.51s ==============================

Usage

cd examples/python/clients/advanced
cp .env-local .env  # Add your private key

uv sync
uv run python index.py hooks    # Run specific example
uv run python index.py all      # Run all examples
uv run pytest tests/ -v         # Run tests

Checklist

• Commit signed
• Based on feat/python-v2-sdk branch
• Separate directory structure
• pyproject.toml with uv sync support
• Environment variable validation
• Unit tests passing (40/40)

[vercel]

@1bcMax is attempting to deploy a commit to the Coinbase Team on Vercel.

A member of the Team first needs to authorize it.

[phdargen]

This should use the new import pattern for optional dependencies introduced in #901, see eg https://github.com/coinbase/x402/blob/feat/python-v2-sdk/examples/python/clients/httpx/pyproject.toml

Suggested change

	"x402",
	"eth-account>=0.13.0",
	"python-dotenv>=1.0.0",
	"httpx>=0.27.0",
	"x402[evm,svm,httpx]",
	"python-dotenv>=1.0.0",

[phdargen]

Please remove all the tests, these belong in the sdk, not the examples. If you identified any missing test coverage in the sdk, please move them to python/x402/tests

[phdargen]

please also include svm here

[phdargen]

Suggest renaming custom_transport.py -> retry_transport.py

[phdargen]

Suggest renaming custom_transport.py -> retry_transport.py

Actually custom_transport.py fails on runtime with TypeError: AsyncClient.__init__() got an unexpected keyword argument 'httpx_client'. Also not sure about the error_recovery.py example, it doesn't seem to implement any recovery and thus is somewhat duplicate to hooks.py. In any case, the custom_transport.py and error_recovery.py examples go beyond what we currently have in the typescript sdk. I think for the python v2 release it would be best to aim for typescript parity and remove these 2 for now. After the release, we can then add additional examples for all sdks simultaneously, if desired

[phdargen]

Hi @1bcMax, thanks a lot for your contribution! Please have a look at my comments above

[1bcMax]

@phdargen Hey my buddy, i have moved the test code as you suggest.

[phdargen]

Great thanks @1bcMax, could you please also address the other 2 comments above (imports and svm)?

[1bcMax]

Addressed the feedback:

• Updated pyproject.toml to use x402[evm,svm,httpx] optional dependencies
• Added Solana/SVM network examples to preferred_network.py alongside EVM chains
• The example now supports both EVM and Solana signers for cross-chain flexibility

Ready for re-review!

[phdargen]

Thanks for the update @1bcMax, LGTM 🚀