It is our collective responsibility to enforce this Style Guide since our chosen linter does not catch everything.
We use Black as our linter. We use the default configuration.
There is a manual CI job in the
review stage that will lint the entire repo and return a non-zero exit code if files need to be formatted. It is up to both the MR author and the reviewer to make sure that this job passes before the MR is merged. To lint the entire repo, just execute
black . from the top of the repo.
All function signatures should contain type hints, including for the return type, even if it is
None. This is good documentation and can also be used with mypy for type checking and error checking.
def foo(x: int, y: int) -> int: """ Add two numbers together and return. """ return x + y def bar(some_str: str) -> None: """ Print a string. """ print(some_str) return
Imports should follow the PEP8 rules and furthermore should be ordered with any
import ... statements coming before
from .... import ...
import logging import sys from os import environ import pandas as pd from requests import get import some_local_module from another_local_module import something
Docstrings should be used in every single function. Since we are using type hints in the function signature there is no requirement to describe each parameter. Docstrings should use triple double-quotes and use complete sentences with punctuation.
def foo(x: int, y: int) -> int: """ Add two numbers together and return the result. """ return x + y def bar(some_str: str) -> None: """ Print a string. This is another proper sentence. """ print(some_str) return
To make functions as reusable as possible, it is highly discouraged (unless there is a very good reason) from using environment variables directly in functions (there is an example of this below). Instead, the best practice is to either pass in the variable you want to use specifically or pass all of the environment variables in as a dictionary. This allows you to pass in any dictionary and have it be compatible while also not requiring the variables to being defined at the environment level.
import os from typing import Dict ## Don't do this! def foo(x: int) -> int: """ Add two numbers together and return. """ return x + os.environ["y"] foo(1) ## Do this! env_vars = os.environ.copy() # The copy method returns a normal dict of the env vars. def bar(some_str: str, another_string: str) -> None: """ Print two strings concatenated together. """ print(some_str + another_string) return bar("foo", env_vars["bar"]) ## Or do this! def bar(some_str: str, env_vars: Dict[str, str]) -> None: """ Print two strings concatenated together. """ print(some_str + env_vars["another_string"]) return bar("foo", env_vars)
We use a few standard aliases for common third-party packages. They are as follows:
import pandas as pd
import numpy as np
When possible, use descriptive naming for variables, especially with regards to data type. Here are some examples:
data_dfis a dataframe
params_dictis a dictionary
retries_intis an int
bash_command_stris a string
Although usually in the case of constants (particularly strings and numbers) it isn't as helpful, adding the type to the name is good self-documenting code.
If your script is not able to be run even though you've just made it, it most likely needs to be executable. Run the following:
chmod 755 yourscript.py
For an explanation of chmod 755 read this askubuntu page.
Since this style guide is for the entire data team, it is important to remember that there is a time and place for using Python and it is usually outside of the data modeling phase. Stick to SQL for data manipulation tasks where possible.