Errors using TabularProc constructors

Hi, I’m getting an error when I use TabularProcs with a constructor. I’m not sure if it’s a bug or I’m using them wrong.

If I use FillMissing, it works fine. If I use FillMissing(cat_names, cont_names) I get an error suggesting that FillMissing.apply_test() is being called before FillMissing.apply_train(). (I want to use the constructor so I can set parameters such as fill_strategy.)

Reproducible example:

from fastai.tabular import *
path = untar_data(URLs.ADULT_SAMPLE)

# Version of learn() from
# Only modification is extraction of 'procs' as parameter
def learn(procs=[FillMissing, Categorify, Normalize]):
    df = pd.read_csv(path/'adult.csv')
    # procs = [FillMissing, Categorify, Normalize]
    dep_var = 'salary'
    cat_names = ['workclass', 'education', 'marital-status', 'occupation', 'relationship', 'race', 'sex', 'native-country']
    cont_names = ['age', 'fnlwgt', 'education-num']
    test = TabularList.from_df(df.iloc[800:1000].copy(), path=path, cat_names=cat_names, cont_names=cont_names)
    data = (TabularList.from_df(df, path=path, cat_names=cat_names, cont_names=cont_names, procs=procs)
    learn = tabular_learner(data, layers=[200,100], emb_szs={'native-country': 10}, metrics=accuracy)
    learn.fit_one_cycle(2, 1e-2)
    return learn

# cat_names, cont_names copied from learn()
cat_names = ['workclass', 'education', 'marital-status', 'occupation', 'relationship', 'race', 'sex', 'native-country']
cont_names = ['age', 'fnlwgt', 'education-num']

# Succeeds as expected

# Fails (uses FillMissing constructor)
learn([FillMissing(cat_names=cat_names, cont_names=cont_names), Categorify, Normalize])
# AttributeError: 'FillMissing' object has no attribute 'na_dict'

na_dict is set in FillMissing.apply_train(), but I don’t think this method is being called.

Using Categorify(cat_names, cont_names) also fails.

We can make a small class Report to check whether apply_train() or apply_test() are being called:

# Make our own TabularProc subclass to check calls to apply_train and apply_test
class Report(TabularProc):
    def apply_train(self, df:DataFrame):
        print("Hello from TRAIN")
    def apply_test(self, df:DataFrame):
        print("Hello from TEST")

# Prints "Hello from TRAIN"
learn([Report, FillMissing, Categorify, Normalize])
# Hello from TRAIN
# Hello from TEST
# Hello from TEST

# Never prints "Hello from TRAIN"
learn([Report(cat_names=cat_names, cont_names=cont_names), FillMissing, Categorify, Normalize])
# Hello from TEST
# Hello from TEST
# Hello from TEST

Am I using FillMissing etc. wrong?

Thank you!

I was using FillMissing wrong. The user should not call FillMissing's constructor. To use parameters such as fill_strategy, use partial:

from functools import partial
procs = [partial(FillMissing, fill_strategy=FillStrategy.CONSTANT), Categorify, Normalize]