Revert of Update Python style guide to point out exceptions only apply to legacy scripts

styleguide/styleguide.md

 # Chromium coding style
 
 ## Main style guides
 
   * [Chromium C++ style guide](c++/c++.md)
   * [Google Objective-C style guide](https://google.github.io/styleguide/objcguide.xml)
   * [Java style guide for Android](https://sites.google.com/a/chromium.org/dev/developers/coding-style/java)
   * [GN style guide](../tools/gn/docs/style_guide.md) for build files
 
 Chromium also uses these languages to a lesser degree:
 
   * [Kernel C style](https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/CodingStyle?id=refs/heads/master) for ChromiumOS firmware.
   * [IDL](https://sites.google.com/a/chromium.org/dev/blink/webidl#TOC-Style)
   * [Jinja style guide](https://sites.google.com/a/chromium.org/dev/developers/jinja#TOC-Style) for [Jinja](https://sites.google.com/a/chromium.org/dev/developers/jinja) templates.
 
 ## Python
 
-Python code should follow [PEP-8](https://www.python.org/dev/peps/pep-0008/).
-
-Some existing scripts were originally written following Google's internal
-style guideline and have the following two exceptions. New scripts should,
-however, be PEP-8 compliant.
+Python code should follow [PEP-8](https://www.python.org/dev/peps/pep-0008/),
+except:
 
   * Use two-space indentation instead of four-space indentation.
   * Use `CamelCase()` method and function names instead of `unix_hacker_style()` names.
 
+(The rationale for these is mostly legacy: the code was originally written
+following Google's internal style guideline, the cost of updating all of the
+code to PEP-8 compliance was not small, and consistency was seen to be a
+greater virtue than compliance.)
+
 [Depot tools](http://commondatastorage.googleapis.com/chrome-infra-docs/flat/depot_tools/docs/html/depot_tools.html)
 contains a local copy of pylint, appropriately configured.
 
 Note that asserts are of limited use, and should not be used for validating
 input – throw an exception instead. Asserts can be used for validating program
 logic, especially use of interfaces or invariants (e.g., asserting that a
 function is only called with dictionaries that contain a certain key). [See
 Using Assertions
 Effectively](https://wiki.python.org/moin/UsingAssertionsEffectively).
 
 See also the [Chromium OS Python Style
 Guidelines](https://sites.google.com/a/chromium.org/dev/chromium-os/python-style-guidelines).
 
 ## Web languages (JavaScript, HTML, CSS)
 
 When working on Web-based UI features, consult the [Web Development Style Guide](https://sites.google.com/a/chromium.org/dev/developers/web-development-style-guide) for the Chromium conventions used in JS/CSS/HTML files.
 
 Internal uses of web languages, notably "layout" tests, should preferably follow these style guides, but it is not enforced.