Pandas save date in ISO format?

Question

I am trying to create a Pandas DataFrame where date_range is the index. Then save it in a CSV file so that the dates are recorded in ISO-8601 format.

import pandas as pd
import numpy as np
from pandas import DataFrame, Series

NumberOfSamples = 10
dates = pd.date_range('20130101',periods=NumberOfSamples,freq='90S')
df3 = DataFrame(index=dates)
df3.to_csv('dates.txt', header=False)

The current output to the date file. txt:

2013-01-01 00:00:00
2013-01-01 00:01:30
2013-01-01 00:03:00
2013-01-01 00:04:30
...................

I am trying to make it look like this:

2013-01-01T00:00:00Z
2013-01-01T00:01:30Z
2013-01-01T00:03:00Z
2013-01-01T00:04:30Z
....................

Answer 1

Use datetime.strftimeand call mapby index:

In [72]:

NumberOfSamples = 10
import datetime as dt
dates = pd.date_range('20130101',periods=NumberOfSamples,freq='90S')
df3 = pd.DataFrame(index=dates)
df3.index = df3.index.map(lambda x: dt.datetime.strftime(x, '%Y-%m-%dT%H:%M:%SZ'))
df3
Out[72]:
Empty DataFrame
Columns: []
Index: [2013-01-01T00:00:00Z, 2013-01-01T00:01:30Z, 2013-01-01T00:03:00Z, 2013-01-01T00:04:30Z, 2013-01-01T00:06:00Z, 2013-01-01T00:07:30Z, 2013-01-01T00:09:00Z, 2013-01-01T00:10:30Z, 2013-01-01T00:12:00Z, 2013-01-01T00:13:30Z]

Alternatively and better in my opinion (thanks @unutbu) you can pass the format specifier to_csv:

df3.to_csv('dates.txt', header=False, date_format='%Y-%m-%dT%H:%M:%SZ')