Erik Reinertsen     Blog     Tech     Research     Talks

Python style preferences

I have adopted the following Python style preferences, many of which are from working with the excellent engineers at the Broad Institute.

  1. Global variables are in upper-case, can be accessed anywhere within a script, and should be initialized at the top of the script.

    Good global variables are paths to file names, e.g.
    FNAME_RESULTS = "./results".

    Minimize use of global variables.

  2. Functions only called within a script are private functions, whereas scripts imported into other scripts are not private.

    Private functions start with an underscore, e.g. def _calculate_auc(args): and auc = _calculate_auc(args).

    Non-private functions (e.g. those defined in that are used elsewhere via from utils import func) do not need an underscore, e.g. load_data(args).

  3. Use"content") instead of print.

    Printing to the screen slows down scripts, so only do it when necessary. Most results and certainly figures should be saved in a file. Print the bare essentials to screen.

  4. Use f-strings, not %-strings:

     print(f"classifier: {clf_name} / train AUC {auc_train}")

    %-strings are slower and less readable:

     print("classifier: %s / train AUC %s " % (clf_name, auc_train))
  5. Use double-quotes for strings, not single-quotes, e.g. "this is good" and 'this is bad'. Other languages use double-quotes, and even within Python there are string formatting situations where double-quotes make life easier.

  6. Use type hints instead of verbose variable / argument names or function documentation. You can indicate types and default values in function definitions:

     def calc_op_time(name: str = "bob", op_time: float = 60.0) -> str:
         new_val = str(op_time**2)
         return f"patient {name}'s op time squared is: {new_val}"