Why do I get a 'FutureWarning' with pandas.concat?

Question

Does anyone meet this similar FutureWarning? I got this when I was using Tiingo+pandas_datareader?

The warning is like:

python3.8/site-packages/pandas_datareader/tiingo.py:234: FutureWarning: In a future version of pandas all arguments of concat except for the argument 'objs' will be keyword-only
    return pd.concat(dfs, self._concat_axis)

I think this warning does not impact my accessing to pandas data(in my case, I fetch from tiingo api), I can get all the data I want with no problem. I just want to understand if there is any risk with my current enviroment:

my python3                -  3.8.5, 
Python 3.8.5, pytest-6.2.4, py-1.10.0, pluggy-0.13.1
pandas_datareader version -  0.10.0
pandas version            -  1.3.2

I then tested my code with a 'futureVersion' of python: 3.9.6 (comparing with python 3.8.5). To my suprise, I no longer get any warning or error, everything works fine:

bellow are details updated

platform win32 
- Python 3.9.6, pytest-6.2.4, py-1.10.0, pluggy-0.13.1

Any advice is appreciated.

Stateroom

Answer 1

Most function parameters in python are "positional or keyword" arguments.

I.e. if I have this function:

def do_something(x, y):
    pass

Then I can either call it like this, using positional arguments:

do_something(1, 2)

Or like this, using keyword arguments:

do_something(x=1, y=2)

Or like this, using a mixture of the two (but note that you're not allowed to have a positional argument after a keyword argument):

do_something(1, y=2)

But you can also define functions with positional-only or keyword-only parameters

Say I have this other function:

def do_something_else(x, /, y, *, z):
    pass

In this function, I've marked x as being positional-only, because it comes before the /. And I've marked z as being keyword-only, because it comes after the *. y is a positional-or-keyword parameter, as it comes after the / but before the *. This means that these two attempts to call the function will fail: the first one because z is being called as a positional argument, and the second because x is being called as a keyword argument:

do_something_else(1, 2, 3)       # will fail!
do_something_else(x=1, y=2, z=3) # will fail!

These two attempts, however, will both succeed — y is still a positional-or-keyword parameter.

do_something_else(1, 2, z=3)     # fine
do_something_else(1, y=2, z=3)   # fine

The `FutureWarning` message.

The FutureWarning message has nothing to do with the version of python you're using, but has everything to do with the version of pandas that you're using. Pandas is a third-party library, not a part of the python core, so the pandas version you're using is a completely different thing to the python version you're using.

The warning is letting you know that currently, you're fine to write pd.concat(dfs, self._concat_axis), but that they're planning on changing the definition of the function in a future version of pandas so that all arguments except for objs will be keyword-only. I.e., after they make this change, pd.concat(dfs, self._concat_axis) will raise an error, and you will have to write pd.concat(dfs, axis=self._concat_axis) instead. They are most likely considering making this change because calling functions with keyword arguments is often clearer and more readable for other people.

Primordium

hi Alex, this perfectly answer my question, appreciate! – Stateroom

Congrats, Alex! Could you also explain how to silence this warning? – Sanitation

@Sanitation just use a keyword argument in your function call! – Primordium