Update train.py

[gszh]

Add user-defined hooks.

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Merging #428 (7aba32a) into master (7e1b24d) will decrease coverage by 0.15%.
The diff coverage is 30.76%.

❗ Current head 7aba32a differs from pull request most recent head a7f1ded. Consider uploading reports for the commit a7f1ded to get more accurate results

@@            Coverage Diff             @@
##           master     #428      +/-   ##
==========================================
- Coverage   86.44%   86.29%   -0.16%     
==========================================
  Files          97       97              
  Lines        4958     4969      +11     
  Branches      805      807       +2     
==========================================
+ Hits         4286     4288       +2     
- Misses        517      526       +9     
  Partials      155      155              

Flag	Coverage Δ
unittests	86.29% <30.76%> (-0.16%)	⬇️

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Impacted Files	Coverage Δ
mmseg/apis/train.py	22.22% <18.18%> (-2.78%)	⬇️
mmseg/models/decode_heads/fcn_head.py	100.00% <100.00%> (ø)

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[Junjun2016]

Hi @gszh
Thanks for your contribution and sorry for the late reply.
Nice PR and looking forward to your PR again.

[Junjun2016]

#1001

[OpenMMLab-Assistant-007]

Hi!
@gszh
First of all, we want to express our gratitude for your significant PR in the OpenMMLab project. Your contribution is highly appreciated, and we are grateful for your efforts in helping improve this open-source project during your personal time. We believe that many developers will benefit from your PR.

We would also like to invite you to join our Special Interest Group (SIG) private channel on Discord, where you can share your experiences, ideas, and build connections with like-minded peers. To join the SIG channel, simply message moderator— OpenMMLab on Discord or briefly share your open-source contributions in the #introductions channel and we will assist you. Look forward to seeing you there! Join us ：https://discord.gg/UjgXkPWNqA

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Thank you again for your contribution❤