How to convert DataFrame.append() to pandas.concat()?

You can store the DataFrames generated in the loop in a list and concatenate them with features once you finish the loop.

In other words, replace the loop:

for count in range(num_samples):
    # .... code to produce `input_vars`
    features = features.append(input_vars)        # remove this `DataFrame.append`

with the one below:

tmp = []                                  # initialize list
for count in range(num_samples):
    # .... code to produce `input_vars`
    tmp.append(input_vars)                        # append to the list, (not DF)
features = pd.concat(tmp)                         # concatenate after loop

You can certainly concatenate in the loop but it’s more efficient to do it only once.