pandas fill missing dates in time series

Question

I have a dataframe which has aggregated data for some days. I want to add in the missing days

I was following another post, Add missing dates to pandas dataframe, u

Answer 1

From cᴏʟᴅsᴘᴇᴇᴅ's hints in the comments:

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resample fits well here.

Resample: Convenience method for frequency conversion and resampling of time series. Object must have a datetime-like index (DatetimeIndex, PeriodIndex, or TimedeltaIndex), or pass datetime-like values to the on or level keyword.

import random
import datetime as dt
import numpy as np
import pandas as pd

def generate_row(year, month, day):
    while True:
        date = dt.datetime(year=year, month=month, day=day)
        data = np.random.random(size=4)
        yield [date] + list(data)

# days I have data for
dates = [(2000, 1, 1), (2000, 1, 2), (2000, 2, 4)]
generators = [generate_row(*date) for date in dates]

# get 5 points for each
data = [next(generator) for generator in generators for _ in range(5)]

# make dataframe
df = pd.DataFrame(data, columns=['date'] + ['f'+str(i) for i in range(1,5)])

# using the resample method
df.set_index(df.date, inplace=True)
df = df.resample('D').sum().fillna(0)