[Enhancement] Enhance the output of exception

[zhouzaida]

Thanks for your contribution and we appreciate it a lot. The following instructions would make your pull request more healthy and more easily get feedback. If you do not understand some items, don't worry, just make the pull request and seek help from maintainers.

Motivation

Enhance the output of exceptions. Related Issue #1308

Modification

update the mmcv/utils/config.py

BC-breaking (Optional)

No

Checklist

Before PR:

• I have read and followed the workflow indicated in the CONTRIBUTING.md to create this PR.
• Pre-commit or linting tools indicated in CONTRIBUTING.md are used to fix the potential lint issues.
• Bug fixes are covered by unit tests, the case that causes the bug should be added in the unit tests.
• New functionalities are covered by complete unit tests. If not, please add more unit test to ensure the correctness.
• The documentation has been modified accordingly, including docstring or example tutorials.

After PR:

• If the modification has potential influence on downstream or other related projects, this PR should be tested with some of those projects, like MMDet or MMCls.
• CLA has been signed and all committers have signed the CLA in this PR.

[codecov]

Codecov Report

Merging #1309 (291662f) into master (e621e08) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 291662f differs from pull request most recent head 1917957. Consider uploading reports for the commit 1917957 to get more accurate results

@@           Coverage Diff           @@
##           master    #1309   +/-   ##
=======================================
  Coverage   68.81%   68.81%           
=======================================
  Files         161      161           
  Lines       10742    10743    +1     
  Branches     1972     1972           
=======================================
+ Hits         7392     7393    +1     
  Misses       2962     2962           
  Partials      388      388           

Flag	Coverage Δ
unittests	68.81% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
mmcv/utils/config.py	90.12% <100.00%> (+0.02%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update e621e08...1917957. Read the comment docs.