Where to hold common strftime strings like ("%d/%m/%Y")

Question

In my app I find myself using stftime a lot, and mostly with 2 strings formats - ("%d/%m/%Y") and ("%H:%M")

Instead of writing the string each time, I want to store those strings in some global var or something, so I can define the format strings in just one place in my app.

What is the pythonic way of doing that? Should I use a global dict, a class, a function, or maybe something else?

Maybe like this?

class TimeFormats():
    def __init__(self):
        self.date = "%d/%m/%Y"
        self.time = "%H:%M"

Or like this?

def hourFormat(item):
    return item.strftime("%H:%M")

Thanks for the help

Answer 1

you could use functools.partial to generate a function holding the format:

import time,functools

time_dhm = functools.partial(time.strftime,"%d/%m/%Y") 
time_hm = functools.partial(time.strftime,"%H:%M")

print(time_dhm(time.localtime()))
print(time_hm(time.localtime()))

result:

18/01/2017
10:38

you only have to pass the time structure to the new function. The function holds the format.

Note: you can do the same with lambda:

time_dhm = lambda t : time.strftime("%d/%m/%Y",t)

Answer 2

I think it is better to create a custom function to achieve this. For example:

def datetime_to_str(datetime_obj):
    return datetime_obj.strftime("%d/%m/%Y")

Sample run:

>>> from datetime import datetime

>>> datetime_to_str(datetime(1990, 3, 12))
'12/03/1990'

It will be much more friendly for the fellow developers as the function name is self explanatory. Each time conversion of datetime to str is needed, they will know which function is needed to be called. And in case you want to change the format through out the application; there will be single point of change.

Answer 3

You could create your own settings module, like django does.

settings.py:

# locally customisable values go in here
DATE_FORMAT = "%d/%m/%Y"
TIME_FORMAT = "%H:%M"
# etc.
# note this is Python code, so it's possible to derive default values by 
# interrogating the external system, rather than just assigning names to constants.

# you can also define short helper functions in here, though some would
# insist that they should go in a separate my_utilities.py module.

# from moinuddin's answer

def datetime_to_str(datetime_obj):
    return datetime_obj.strftime(DATE_FORMAT)

elsewhere

from settings import DATE_FORMAT
...
time.strftime( DATE_FORMAT, ...)

or

import settings
...
time.strftime( settings.DATE_FORMAT, ...)