Python: tell my IDE what type an object is

Question

When I write a function in Python (v2.7), I very often have a type in mind for one of the arguments. I'm working with the unbelievably brilliant pandas library at the movemement, so my arguments are often 'intended' to be pandas.DataFrames.

In my favorite IDE (Spyder), when you type a period . a list of methods appear. Also, when you type the opening parenthesis of a method, the docstring appears in a little window.

But for these things to work, the IDE has to know what type a variable is. But of course, it never does. Am I missing something obvious about how to write Pythonic code (I've read Python Is Not Java but it doesn't mention this IDE autocomplete issue.

Any thoughts?

Answer 1

I don't know if it works in Spyder, but many completion engines (e.g. Jedi) also support assertions to tell them what type a variable is. For example:

def foo(param):
    assert isinstance(param, str)
    # now param will be considered a str
    param.|capitalize
           center
           count
           decode
           ...

Answer 2

Actually I use IntelliJ idea ( aka pyCharm ) and they offer multiple ways to specify variable types:

1. Specify Simple Variable

Very simple: Just add a comment with the type information behind the definition. From now on Pycharm supports autcompletition! e.g.:

def route():
    json = request.get_json() # type: dict

Source: https://www.jetbrains.com/help/pycharm/type-hinting-in-pycharm.html

2. Specify Parameter:

Add three quote signs after the beginning of a method and the idea will autocomplete a docstring, as in the following example:

Source: https://www.jetbrains.com/help/pycharm/using-docstrings-to-specify-types.html

(Currently on my mobile, going to make it pretty later)