[Bug]: v1.7.0 silently broke api_url values containing /v3 [breaking change]

[arbroen]

Version

1.7

Operating System

Linux

Python Version

3.14

What happened?

Summary

v1.6.0 built per-version URLs with urljoin:

v3_base = urljoin(self.api_url, "v3/")

urljoin("https://api.eu.mailgun.net/v3", "v3/") 
#  "https://api.eu.mailgun.net/v3/" 
# the relative v3/ replaces the trailing segment, so an api_url containing /v3 worked fine.

v1.7.0 switched to f-string concat:

self._baked_urls = {ver.value: f"{self.api_url}/{ver.value}" for ver in APIVersion}

# Now /v3 is appended unconditionally 
# https://api.eu.mailgun.net/v3/v3/... → every request 404s.

Since this is missing from the Changelog or releases info I'm assuming this is regression.

Kind regards

Steps to reproduce

Use https://api.eu.mailgun.net/v3/ as a base_url.

Relevant log output

Additional information

No response

[skupriienko-mailgun]

Hi @arbroen,

Thanks for the spot-on bug report! You absolutely nailed the diagnosis — this is a regression caused by swapping urljoin for f-strings in v1.7.0.

We moved to pre-baked $O(1)$ routing to achieve a ~50x speedup. However, urljoin had a hidden quirk — it treated URLs without trailing slashes as files and silently overwrote the explicitly passed /v3 suffix. Removing urljoin removed this "safety net," causing the /v3/v3 duplication.

The Fix #41: We've introduced a strict parsing phase during initialization. The SDK now detects and cleanly strips trailing versions (like /v3) to maintain backward compatibility. It also emits a non-breaking logging.warning to gently guide developers toward using the base host.

This will be available in v1.7.1, planned for next week.

Thanks again for the excellent debugging!

[arbroen]

Hello sir,

Thank you for the fast response and kind words.

Have you seen the documentation/README.md usecase? This example includes the v3 version information. I suspect this is where my configuration stems from. I haven't ran your code but when reading it it seems to raise an error when it includes the version information in every case?

Obviously, I leave it up to your discretion.

[skupriienko-mailgun]

Hi @arbroen,
You just found the missing puzzle piece! Thank you for pointing this out. I checked the README.md, and you are completely right — our own documentation explicitly taught developers to include the /v3 suffix in the api_url. That explains exactly why your configuration was structured that way.
To clarify how the new patch handles this: it will not break your current code. If the SDK detects a trailing version (like https://api.eu.mailgun.net/v3), it will safely strip the /v3 to prevent the 404 error, and your requests will continue to work perfectly. It will only raise a hard ApiError if a version is trapped in the middle of a complex proxy path (e.g., /v3/sandbox/), where the SDK cannot safely determine your routing intent.
I'm pushing an update to the README.md right now to fix the examples so future users don't run into this. Brilliant catch — thank you for helping us trace and clean up this technical debt!