Code Style¶

Respect the project code style.
A summary of the project code style is:
- Spacing: Use spaces between identifiers and other tokens. Modern writing systems use this convention, which emerged around the 7th century of the Common Era, to improve readability. Computer code can generally be written this way too… also to improve readability.
- Line Width: Follow PEP 8 on this: no more than 79 columns for code lines. Consider how long lines affect display on laptops or side-by-side code panes with enlarged font sizes. (Enlarged font sizes are used to reduce eye strain and allow people to code without visual correction.)
- Vertical Compactness.
  - Function definitions, loop bodies, and condition bodies, which consist of a single statement and which are sufficiently short, should be placed on the same line as the statement that introduces the body.
  - Blank lines should not be used to group statements within a function body. If you need to group statements within a function body, then perhaps the function should be refactored.
  - Function bodies should not be longer than thirty lines. I.e., one should not have to scroll to read a function.
Pull requests, which attempt to enforce the Python black style or any style other than the project code style, will be rejected.

Todo

Rust Guidance

Specific Preferences¶

Class and Function Definitions¶

Keep all arguments on one line if they fit within the line limit:

def simple_function( arg1: int, arg2: str = 'default' ) -> bool:
    return True

When arguments must be split across lines, prefer to group positional and nominative arguments:

def medium_function(
    first_pos, second_pos, third_pos,
    first_named = 'default', second_named = 'other'
) -> None: pass

When grouping would overflow a line, place each argument on its own line:

def complex_function(
    first_very_long_positional_argument: dict,
    second_very_long_positional_argument: list,
    first_named_arg = 'some very long default value',
    second_named_arg = 'another long default value',
) -> None: pass

For single-line function bodies, especially pass, keep them on the same line as the definition when possible:

def simple_operation( value: int ) -> int: return value * 2

def stub_function( data: bytes ) -> None: pass

When a single-line form would overflow, always go to the a three-or-more-line form with the arguments on indented lines between the first and last lines. There is no two-line form. I.e., do this:

def semicomplex_function(
    argument_1: int, argument_2: int, argument_3: str
) -> bool: return True

and not this:

def semicomplex_function( argument_1: int, argument_2: int, argument_3: str
) -> bool: return True

Collections¶

For short collections, keep them on one line:

points = [ ( 1, 2 ), ( 3, 4 ), ( 5, 6 ) ]

config = { 'name': 'example', 'value': 42 }

For longer collections, split elements one per line with a trailing comma after the last element:

matrix = [
    [ 1, 2, 3, 4 ],
    [ 5, 6, 7, 8 ],
    [ 9, 10, 11, 12 ],
]

settings = {
    'name': 'example',
    'description': 'A longer example that needs multiple lines',
    'values': [ 1, 2, 3, 4, 5 ],
    'nested': {
        'key1': 'value1',
        'key2': 'value2',
    },
}

Docstrings¶

Use triple single-quotes for all docstrings.
For single-line docstrings, include one space after the opening quotes and before the closing quotes:
```
def example_function( ):
    ''' An example function. '''
```

For multi-line docstrings, include a newline after the heading and before the closing quotes. Indent continuation lines to match the opening quotes:

class ExampleClass:
    ''' An example class.

        This class demonstrates proper docstring formatting
        with multiple lines of documentation.
    '''

Place the closing triple quotes on their own line for multi-line docstrings, indented to match the opening quotes.

Imports¶

The project has an internals subpackage, __, which contains all common third-party imports. If your desired import is in this subpackage, then you can import this subpackage near the top of the module under development; e.g.:

from . import __

If the internals subpackage does not have your desired import, consider whether it is a common third-party import, which is likely to be used in other modules in the future, or whether it is something specialized. If it is a common third-party import, then add it to the imports in the internals subpackage, using an abbreviated alias if the name is long. (E.g., cabc as an alias for collections.abc.)

If your desired import is specialized for the current module, then consider how widely it will be used within the module. If only one or two functions will need it and they are not performance-critical, then consider importing from within the function bodies. (Function-level imports reduce module namespace pollution and make functions more relocatable since their requisite imports will move with them.) Otherwise, import at the top of the module, aliasing the import so that it is private and will not pollute the public API of the module.

Example of function-level imports:

def process_data( raw_data: bytes ) -> dict:
    from tomli_w import dumps
    from .utils import decode_packet
    # Function implementation...

Example of private module-level import aliases:

import aiofiles as _aiofiles

from . import exceptions as _exceptions

Note

The above advice does not apply to modules in a test suite. As test modules are not intended to expose public APIs, feel free to follow the common practice of placing public imports at the tops of those modules.

Follow the import grouping conventions from PEP 8:

# __future__ from imports

# standard library imports

# standard library from imports

# third-party imports

# third-party from imports

# first-party relative imports

# first-party relative from imports

For import sequences, which will not fit on one line, use parentheses with hanging indent:

from third_party.submodule import (
    FirstClass, SecondClass, ThirdClass )

For import sequences, which will not fit on two lines, list them one per line with a trailing comma after each one and the closing parentheses dedented on a separate line:

from third_party.other import (
    ALongClassName,
    AnotherLongClassName,
    YetAnotherLongClassName,
)

Imports within a sequence should be sorted lexicographically with uppercase letters coming before lowercase ones (i.e., classes and type aliases before functions). Import aliases are relevant to this ordering rather than the imports which they alias.

Line Continuation¶

Use parentheses for line continuation. Split at natural points such as dots, operators, or after commas. Keep the closing parenthesis on the same line as the last element unless the collection has a trailing comma:

# Dot operator splits
result = (
    very_long_object_name.first_method_call( )
    .second_method_call( )
    .final_method_call( ) )

# Operator splits
total = (
    first_long_value * second_long_value
    + third_long_value * fourth_long_value )

# Array subscript splits
element = (
    very_long_array_name[ first_complex_index ]
    [ second_complex_index ]
    [ 'nested_key' ] )

# List/dict comprehension splits
squares = [
    value * value
    for value in range( 100 )
    if is_valid( value ) ]

# Multi-line conditional statements
if (  validate_input( data, strict = True )
      and process_ready( )
): process( data )

Single-Line Statements¶

Keep simple control flow statements on one line when they contain a single simple action:

if not data: return None
while more_items: process_next( )
try: value = next( iterator )
except StopIteration: return

for item in items: yield item
with lock: do_work( )

Similarly, keep simple class and function definitions on one line when their body consists only of pass:

class EmptyMixin: pass

def not_implemented_yet( data: bytes ) -> None: pass

However, if the definition includes type annotations or multiple base classes that would make the line too long, use normal multi-line formatting:

class SimpleContainer(
    Generic[ _T ],
    cabc.Collection,
    metaclass = ImmutableClass
): pass

Spaces¶

One space after opening delimiters ((, [, {) and one space before closing delimiters (``)``, ], }), except inside of f-strings and strings to which .format is applied.

Empty collection literals have a single space between delimiters, ( ), [ ], { }. This includes function definitions and invocations with no arguments.

A space on each side of = for nominative/keyword arguments:

def some_function( magic = 42 ): pass

and not:

def some_function(magic=42): pass

Strings¶

Use single quotes for string literals unless using f-strings, .format method, or exception and logging messages:

name = 'example'
path = 'C:\\Program Files\\Example'

message = f"Processing {name} at {path}"
formatted = "Value: {:.2f}".format( value )

raise ValueError( "Invalid configuration value" )
logger.error( "Failed to process item" )

Do not use function calls or subscripts inside of f-string expressions. These can be opaque to some linters and syntax highlighters. Instead, use strings with the .format method for these cases, where the function calls or subscripts are performed on the arguments to .format. This:

"Values: {values}".format( values = ', '.join( values ) )

and not this:

f"Values: {', '.join( values )}"

Automation¶

Current, there are no tools which can automatically enforce compliance with the above style guidance. However, if you politely ask an LLM, which is good at instruction following, to make your code conform to the guidance, results will generally be good. If you are familiar with isort and yapf, you can also look approximate formatter configurations for these tools.

Cases where manual intervention may be needed:

Multi-line chains of method invocations. (Fluent programming.)
Function declarations with mixed positional and nominative arguments.
Nested data structures with mixed single-line and multi-line sections.

When in doubt, optimize for readability while staying within the general principles outlined in this guide.