Reformatting a list of date strings to day, month, year in Python

问题

I want to change the format of strings in a list. They are dates but have been converted into strings.

I have looked all over for this solution, but there seem to only be answers for a single element.

First I make a series

Date_List = df.loc['receiveddate']
print Date_List

Element1                               2015-06-26
Element2                               2015-06-25
Element3                               2015-06-26
Element4                               2015-06-25
Element5                               2015-06-25
Element6                               2015-07-01

Then I convert it into a list.

Date_List = [str(i) for i in Date_List]

which gives me

['2015-06-26', '2015-06-25', '2015-06-26', '2015-06-25', '2015-06-25', '2015-07-01']

Instead, I want a list of strings that go day, month, year

['06-26-2015', '06-25-2015...etc.]

I've found that the most common suggestion is to use strftime. Trying Date_List = (datetime.datetime.strptime(i, "%B %d-%Y") for i in Date_List) Just gave me ValueError: time data '2015-06-26' does not match format '%B %d-%Y'

So I tried

Date_List = (datetime.datetime.strptime(i, "%Y-%m-%d") for i in Date_List)

This returned ['2015-06-26 00:00:00', '2015-06-25 00:00:00', '2015-06-26 00:00:00', '2015-06-25 00:00:00', '2015-06-25 00:00:00', '2015-07-01 00:00:00']

Does anybody know how to reformat the list? Or perhaps earlier, reformatting the Series? Thank you.

回答1:

You don't even need to use datetime here. Just map those objects to a function that turns them into strings and splits them on the -, then use str.format():

Date_List = ['{}-{}-{}'.format(m,d,y) for y, m, d in map(lambda x: str(x).split('-'), Date_List)]

Also, from your code snippet it looks like you want the month first, not the day.

回答2:

You're almost there. The datetime.datetime.strptime converts a string into datetime object. You need datetime.datetime.strftime to convert it back to string:

Date_List = (datetime.datetime.strptime(i, "%Y-%m-%d") for i in Date_List)
Date_List = (datetime.datetime.strftime(i, "%m-%d-%Y") for i in Date_List)

回答3:

You can solve it by a string point of view

New_Date_List = [d[8:10]+"-"+d[5:7]+"-"+d[:4] for d in Date_List]

回答4:

Change your comprehension to

import datetime
Date_List = [datetime.datetime.strptime(str(i), '%Y-%m-%d').strftime('%m-%d-%Y') for i in Date_List]

回答5:

Regular expressions provide a pretty straightforward solution:

>>> import re
>>> re.sub(r'(\d{4})-(\d{2})-(\d{2})', r'\2-\3-\1', '2015-06-25')
'06-25-2015'

回答6:

While it's not pretty, it should work to generate a month-day-year list.

New_Date_List = [[d][5:7] + '-' + Date_List[d][-2:] + '-' + Date_List[d][:4] for d in Date_List]

来源：https://stackoverflow.com/questions/32258915/reformatting-a-list-of-date-strings-to-day-month-year-in-python