I have date strings like this:

'January 11, 2010'

and I need a function that returns the day of the week, like

'mon', or 'monday'

etc.
I can’t find this anywhere in the Python help.
Anyone? Thanks.

You might want to use strptime and strftime methods from datetime:

>>> import datetime
>>> datetime.datetime.strptime('January 11, 2010', '%B %d, %Y').strftime('%A')
'Monday'

or for 'Mon':

>>> datetime.datetime.strptime('January 11, 2010', '%B %d, %Y').strftime('%a')
'Mon'

use date.weekday()
Return the day of the week as an integer, where Monday is 0 and Sunday is 6.

http://docs.python.org/2/library/datetime.html#datetime.date.weekday

A third-party parser could be used, such as dateutil.

And code for your original question:

>>> from dateutil import parser
>>> parser.parse('January 11, 2010').strftime("%a")
'Mon'
>>> parser.parse('January 11, 2010').strftime("%A")
'Monday'

I think the fastest way to do it like below:

df[Date_Column].dt.weekday_name

>>> import time
>>> dateStr="January 11, 2010"
>>> timestamp = time.strptime(dateStr, '%B %d, %Y')
>>> timestamp
time.struct_time(tm_year=2010, tm_mon=1, tm_mday=11, tm_hour=0, tm_min=0, tm_sec=0, tm_wday=0, tm_yday=11, tm_isdst=-1)

import time

time.strftime('%A')