pandas -- append data to series while increasing datetime index

Question

I have a dataframe

import pandas as pd
import datetime

#Create data
df = {'Day': ['2012-12-29','2013-01-05'],
      'Whatev': [1,0]}
index = range(len(df['Day']))
columns = ['Day','Whatev']
df = pd.DataFrame(df,  index=index, columns=columns)
print(df)
print()

From which I extract the first column as a series:

#Index to datetime
df['Day'] = pd.to_datetime(df['Day'])
df.set_index('Day', inplace=True) #use day as index


#Create series from dataframe column
s = df[df.columns[0]]
print(s)
print()

To which I would like to append zero values at the end. So first I extend the datetime index and then specify the last value as zero:

#Append 1 data to series
last_date = s.iloc[[-1]].index + datetime.timedelta(days=7)
s.append(pd.DataFrame(index=[last_date]))
s.iloc[[-1]]=0
print(s)
print()

Yes, I did not work. During testing, it seemed to work but here, somehow, the dataframe is unchanged. Which is the reason?

Also, is there a smarter way to achieve the result? In fact, if I want to append more than one value, my solution does not look pretty:

#Append many data to series
L = 2 #hoe many zeros
i=0
while i<=L:
    i+=1
    last_date = s.iloc[[-1]].index + datetime.timedelta(days=7)
    s.append(pd.DataFrame(index=[last_date]))   
    s.iloc[[-1]]=0
print(s)

Answer 1

You can simplify your code with setting-with-enlargement:

df['Day'] = pd.to_datetime(df['Day'])
s = df.set_index('Day')['Whatev']

Loop version:

L = 2 #hoe many zeros
i=0
while i<=L:
    i+=1
    last_date = s.index[-1] + pd.Timedelta(days=7)
    s.loc[last_date]=0
print(s)


2012-12-29    1
2013-01-05    0
2013-01-12    0
2013-01-19    0
2013-01-26    0
Name: Whatev, dtype: int64

Non loop version:

#create DatetimeIndex by last value of index and remove first value by indexing
idx = pd.date_range(s.index[-1], periods=4, freq='7d')[1:]
#append Series to original
s = s.append(pd.Series(np.repeat(0, len(idx)), index=idx))
print(s)

2012-12-29    1
2013-01-05    0
2013-01-12    0
2013-01-19    0
2013-01-26    0
dtype: int64