Converting String to datetime Python

Question

How would I convert the string 2014-05-19 to a datetime object in Python if I'm reading it from a csv file? Currently when I specify dtype=None, it reads in 2014-05-19 as a string, not a datetime.

import numpy as np
import datetime

np.genfromtxt(inputFile, dtype=None,delimiter=' ')

File

2014-05-19 10
2014-05-20 11
2014-05-21 12
2014-05-22 13.29
2014-05-23 12.1

where the number after the string is a value associated with the date but not included in the datetime object

dataPoints = np.loadtxt(inputFile, dtype=None,delimiter=' ', converters = {0: datetime.datetime.strptime('%Y-%m-%d')})

I receive the following message: TypeError: strptime() takes exactly 2 arguments (1 given)

how do I specify the format without actually stripping the string?

Why do you have to use numpy? why not open the csv, split by comma, and strptime? — MikeRixWolfe
– MikeRixWolfe, Commented May 28, 2014 at 15:21

Piotr Nawrot · Accepted Answer · 2014-05-28 16:21:30Z

5

If you don't have missing values you can use numpy.loadtxt().

numpy.genfromtxt() also has the converters param. (thx RickyA)

Using 'coverters' param and lambda function:

from datetime import datetime
datestr2num = lambda x: datetime.strptime(x, '%Y-%m-%d')
np.genfromtxt(inputFile, delimiter=' ', converters = {0: datestr2num})

Where 0 is column index.

There is simpler way - use dtype param:

np.genfromtxt(inputFile, dtype=['datetime64[D]', float], delimiter=' ')

or more human readable using ('column name', type) tuple:

np.genfromtxt(inputFile, dtype=[('Date', 'datetime64[D]'),('Value', float)], delimiter=' ')

BTW IMHO Load string as datetime in numpy would be more accurate title.

edited May 28, 2014 at 16:21

answered May 28, 2014 at 13:46

Piotr Nawrot

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7 Comments

Apollo Over a year ago

but will this try to convert my associated value to a date as well?

Piotr Nawrot Over a year ago

I just edited. You indicate which column will be converted by index. So the answer is no :-)

RickyA Over a year ago

BTW. genfromtxt also has the converters param

Apollo Over a year ago

@PiotrNawrot also, would datestr2num = '%Y-%m-%d' suffice?

Apollo Over a year ago

@PiotrNawrot I'm still just a little confused by the datestr2num part, thanks.

|

Lily Mara · Accepted Answer · 2014-05-28 13:45:11Z

0

You should use the strptime function from the datetime module. I'm not sure what the numbers after the space should be, but this will format the year-month-day correctly into a datetime object.

from datetime import datetime

some_date = '2014-05-28'
parsed_date = datetime.strptime(some_date, '%Y-%m-%d')

print(parsed_date)

answered May 28, 2014 at 13:45

Lily Mara

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