The Fuchsia project follows the Google Python style guide{:.external}, with a few refinements.
The Google Python style guide allows more variation (presumably to cover a large breadth of existing source). This guide has a tighter set of choices. So a Fuchsia Python file will also comply with the Google style guide, but a Google Python file might not comply with this guide. See refinements below for details.
Scripts invoked by the build (GN or Ninja) are executed with Python 3.8.
The build system ensures that all python scripts are executed by the interpreter that is intalled as part of a Fuchsia source checkout.
Scripts that are invoked directly should use python
in the shebang and be
compatible with both 2 and 3: #!/usr/bin/env python
.
Developers working on Fuchsia modules may use various platforms. Some platforms include Python 2 and not Python 3 and vice versa. Until Python 3 is included in the prominent development environments we support, we should support Python 2.
While Python 2 is supported, test scripts on both versions.
Any policy change will be reflected in this document.
Multiple inheritance is strongly discouraged. This is for the same reason
listed in the
Google C++ style guide: risk of "diamond" inheritance{:.external}
patterns, which are prone to confusion. If a case is found where avoiding
multiple inheritance is unreasonable, all classes involved must initially
inherit from the base class object
, which governs which multiple inheritance
scheme is used.
In scripts that support Python 2.x (see Python versions),
explicitly declare text strings as unicode and binary data as bytes, using
u""
, unicode()
, unichr()
and b""
, bytes()
, byte()
respectively.
Python 3.x defaults to using Unicode for strings, so this guideline will be
removed when support for Python 2 is dropped.
Yes:
a = u"Hello" # Unicode constant.
b = unicode(foo) # Convert to Unicode.
c = unichr(c) # Convert to Unicode.
d = io.open("bar.txt").read() # Read text as Unicode.
No:
a = "Hello" # Ambiguous (depends on Python version).
b = str(foo) # Convert to ascii.
c = chr(c) # Convert to ascii.
d = open("bar.txt").read() # Read text as ascii.
The following refinements we make to the Google Python style guide are largely choices between variations. For example, if the style guide says you may do A, B, or C we may choose to favor B and avoid the other choices.
Avoid aligning with opening delimiter. Prefer instead to indent using fixed (4 space) indentation.
(See Indentation{:.external} in the Google Python style guide for comparison.)
Avoid creating single line statements, even with if
statements.
Yes:
if foo:
bar(foo)
No:
if foo: bar(foo)
(See Statements{:.external} in the Google Python style guide for comparison.)
In scripts that support Python 2 (see Python versions), type annotations will not be used.
(See Type Annotations{:.external} in the Google Python style guide for comparison.)
Prefer double quotes for strings ("
). Use single quotes when the declaration is
more readable with single quotes. For example, 'The cat said "Meow"'
is more readable
than "The cat said \\"Meow\\""
.
(See Strings{:.external} in the Google Python style guide for comparison.)
Be consistent within a large scope. Avoid displaying small pockets of consistency within Fuchsia. Being consistent within only a single file or directory is not consistency.
Within third_party
, the intent is to follow the existing style for that project
or library. Look for a style guide within that library as appropriate.
(See Parting Words{:.external} in the Google Python style guide.)