fix(python): use '\\' for string escapes

[busunkim96]

https://blog.bazel.build/2021/01/19/bazel-4-0.html

--incompatible_restrict_string_escapes=true. Unnecessary backslashes such as \. in string literals now result in an error, instead of silently being treated as \\.. To fix the error while preserving behavior, manually add another backslash. However, the error often signals the original code needs to be updated.

[codecov]

Codecov Report

Merging #3335 (1d53188) into master (f74d0aa) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #3335   +/-   ##
=========================================
  Coverage     87.13%   87.13%           
  Complexity     6120     6120           
=========================================
  Files           495      495           
  Lines         24174    24174           
  Branches       2638     2638           
=========================================
  Hits          21065    21065           
  Misses         2242     2242           
  Partials        867      867           

---

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 f74d0aa...1d53188. Read the comment docs.