Changing string format (python)

Question

I want to change the string 'datetime.datetime(2018, 4, 15, 12, 59)' into the format '2018-04-15T12:59'.

I created a function that looks like:

def changeDateFormat(date):
    newDate = []
    for i in date.split('datetime')[2].split(','):
        newDate.append(re.sub('[() ]', '', i))
    newStr = newDate[0] + '-0' + newDate[1] + '-' + newDate[2] + 'T' + newDate[3] + ':' + newDate[4]
    return newStr

And it works.

However, I also want it to handle the case where if each unit is less than 10, I want to add a '0'. Right now it just adds a '0' regardless.

I can do it in a very inefficient way, but I wonder how I can do it in a smart way.

The nicer solution is avoiding ending up with the `repr` of a datetime object in the first place. — miradulo, Apr 16 '18 at 02:09
I'm really with @miradulo on this. Must you work with a `repr`-string? Why can't you have accesses to the actually `datetime` object? — Christian Dean, Apr 16 '18 at 02:11

Zulu · Accepted Answer · 2018-04-16T02:14:55.083

1

I don't understand why you use the string representation of a datetime object but eval is your friend:

>>> import datetime
>>> eval('datetime.datetime(2018, 4, 15, 12, 59)').isoformat()
'2018-04-15T12:59:00'

eval documentation: https://docs.python.org/3/library/functions.html#eval

edited Apr 16 '18 at 02:14

answered Apr 16 '18 at 02:13

Zulu

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_"but eval is your friend"_ - Eh, I'd really advise not to use `eval` here - or anywhere. There's almost always a better way then using `eval`. It may be tempting to use `eval`, but I'd find something different instead. Please see [_Why is using 'eval' a bad practice? _](https://stackoverflow.com/questions/1832940/why-is-using-eval-a-bad-practice) – Christian Dean Apr 16 '18 at 02:17

score 1 · Answer 2 · answered Apr 16 '18 at 02:19

I assume that you're trying to avoid using the datetime object, because it seems obviously confusing otherwise.

I can do it in a very inefficient way

You are actually not very far away, just one line.

def changeDateFormat(date):
    newDate = []
    for i in date.split('datetime')[2].split(','):
        newDate.append(re.sub('[() ]', '', i))

    pad = '-0' if newDate[1] < 10 else '-'
    newStr = newDate[0] + pad + newDate[1] + '-' + newDate[2] + 'T' + newDate[3] + ':' + newDate[4]
    return newStr

I'm afraid there isn't any smarter way if you're not using the datetime object.

Not that I really think the OP should be doing it this way (he really should try to get the actually `datetime` object and not the `repr`), but you could use `re.findall` to grab the digits and avoid all that substitution stuff with `re.sub`. — Christian Dean, Apr 16 '18 at 02:23

score 1 · Answer 3 · answered Apr 16 '18 at 02:22

1

datetime.strftime and eval would be perfect here.

import datetime
# use eval to execute the string like a a command
dt = eval('datetime.datetime(2018, 4, 15, 12, 59)')

formatted_date = dt.strftime('%Y-%m-%dT%H:%M')

output: '2018-04-15T12:59'

Reference: strftime() and strptime() Behavior

answered Apr 16 '18 at 02:22

GalacticRaph

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I know it's tempting, but it really is best to avoid using `eval`. Please see [_Why is using 'eval' a bad practice?_](https://stackoverflow.com/questions/1832940/why-is-using-eval-a-bad-practice). – Christian Dean Apr 16 '18 at 02:23
Well of course it would be a case by case scenario on whether eval is bad or not. In OP's case I don't see how using `eval` is bad. However, I understand the debate and why it should generally be avoided. – GalacticRaph Apr 16 '18 at 02:27

Changing string format (python)

3 Answers3