Pythonic insertion of variable number of arguments into a string

Question

What is the most pythonic way to insert a variable number of arguments into a string?

For example:

Given a variable date format that may be of the form: YYYY-MM-DD,YYYY-MM-DD HH,YYYY-MM-DD HH:MM or YYYY-MM-DD HH:MM:SS.

I would like to insert the values for year, month, day, hour, minute, second into a string, similar to a statement like this:

"%d/%d/%d %d:%d:%d" % (variable number of arguments here)

Such that a print statement of the above string would output a date which, where possible, the actual values are inserted, and if they are not available, a default value of 0 is inserted.

Please note I am not looking for a solution to this particular example, I am looking for a solution to the more general question I state at the beginning (which should work for the example provided). I'm also looking for a solution that doesn't involve an if...elif...else block.

I think keyword arguments are what you're looking for.

Ajean
– Ajean

2014-10-24 01:27:36 +00:00
Commented Oct 24, 2014 at 1:27 — Ajean
– Ajean, Commented Oct 24, 2014 at 1:27
I have expanded my answer further, how is that?

Aaron Hall
– Aaron Hall ♦

2014-10-24 01:38:15 +00:00
Commented Oct 24, 2014 at 1:38 — Aaron Hall
– Aaron Hall ♦, Commented Oct 24, 2014 at 1:38

Aaron Hall · Accepted Answer · 2014-10-24 01:37:54Z

It's more Pythonic to use the str.format method rather than the old %s printf style from C. It's also more Pythonic to use the builtin modules:

>>> import datetime
>>> args1 = 2014, 10, 01
>>> args2 = 2014, 10, 01, 12
>>> args3 = 2014, 10, 01, 12, 25
>>> '{0}'.format(datetime.datetime(*args1))
'2014-10-01 00:00:00'
>>> '{0}'.format(datetime.datetime(*args2))
'2014-10-01 12:00:00'
>>> '{0}'.format(datetime.datetime(*args3))
'2014-10-01 12:25:00'

If you want a more generalized answer to

What is the most pythonic way to insert a variable number of arguments into a string?

Then you could define a function to do that, with positional arguments for the required arguments, and keyword arguments for the optional arguments:

def format_args(arg1, arg2, arg3, arg4=0, arg5=0, arg6=0):
    return '{0}, {1}, {2}, {3}, {4}, {5}'.format(
      arg1, arg2, arg3, arg4, arg5, arg6)

usage:

>>> format_args(*args1)
'2014, 10, 1, 0, 0, 0'
>>> format_args(*args2)
'2014, 10, 1, 12, 0, 0'
>>> format_args(*args3)
'2014, 10, 1, 12, 25, 0'

engineerC · Accepted Answer · 2014-10-24 01:31:31Z

Agree that using datetime is preferable to home rolled solutions. To answer the more general question of interpolating variable arguments in format strings that have different numbers of arguments: the % operator requires a specific number of arguments, but string.format only requires the minimum number. Provide a function that will pad your starting arguments to the longest possible with defaults, then you can feed that to format.

from itertools import chain

date_only = [ 2014, 2, 29 ]
date_and_time = [ 2014, 10, 23, 4, 20, 0 ]
defaults = [ 0 ] * 6 # the most arguments your format string requires

date_strs = [ "{} {} {}", "{} {} {} {} {} {}" ]

for s in date_strs:
    print(s.format(*chain(date_only, defaults)))
    print(s.format(*chain(date_and_time, defaults)))

Output:

2014 2 29
2014 10 23
2014 2 29 0 0 0
2014 10 23 4 20 0

Collectives™ on Stack Overflow

Pythonic insertion of variable number of arguments into a string

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related