styleguide-Style-guides-for-Google-originated-open #

All new code should contain the following and existing code should be updated to be compatible when possible:

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

If you are not already familiar with those, read up on each here: absolute imports, new / division behavior, and the print function.

2.21.1 Definition #

Type annotations (or “type hints”) are for function or method arguments and return values:

def func(a: int) -> List[int]:

You can also declare the type of a variable using a special comment:

a = SomeFunc() # type: SomeType

2.21.2 Pros #

Type annotations improve the readability and maintainability of your code.

import collections
import queue
import sys
from absl import app
from absl import flags
import bs4
import cryptography
import tensorflow as tf
from book.genres import scifi
from myproject.backend.hgwells import time_machine
from myproject.backend.state_machine import main_loop
from otherproject.ai import body
from otherproject.ai import mind
from otherproject.ai import soul
# Older style code may have these imports down here instead:
#from myproject.backend.hgwells import time_machine
#from myproject.backend.state_machine import main_loop

3.14 Statements #

Generally only one statement per line.

Yes:
if foo: bar(foo)

No:
if foo: bar(foo)
else: baz(foo)
try: bar(foo)
except ValueError: baz(foo)
try:
bar(foo)
except ValueError: baz(foo)

3.15 Accessors #

If an accessor function would be trivial, you should use public variables instead of accessor functions to avoid the extra cost of function calls in Python. Example:

from typing import List, TypeVar
T = TypeVar("T")
...
def next(l: List[T]) -> T:
return l.pop()

A TypeVar can be constrained:

AddableType = TypeVar("AddableType", int, float, Text)
def add(a: AddableType, b: AddableType) -> AddableType:
return a + b

A common predefined type variable in the typing module is AnyStr.

from typing import Text, Union
...
def py2_compatible(x: Union[bytes, Text]) -> Union[bytes, Text]:
...
def py3_only(x: Union[bytes, str]) -> Union[bytes, str]:
...

If all the string types of a function are always the same, for example if the return type is the same as the argument type in the code above, use AnyStr. Ex:

from typing import Any, Dict, Optional

Given that this way of importing from typing adds items to the local namespace, any names in typing should be treated similarly to keywords, and not be defined in your Python code, typed or not.