Conditionally including additional characters using python string formatting

Question

Is it possible using python's string format to conditionally include additional characters along with the string variable only if the variable is not empty?

>>> format_string = "{last}, {first}"
>>> name = {'first': 'John', 'last':'Smith'}
>>> format_string.format(**name)
'Smith, John' # great!
>>> name = {'first': 'John', 'last':''}
>>> format_string.format(**name)
', John' # don't want the comma and space here, just 'John'

I would like to use the sameformat_string variable to handle any combination of empty or non-empty values for first or last in the name dict.

What's the easiest way to do this in python?

Aamir Rind · Accepted Answer · 2014-07-05 23:21:24Z

6

Why don't you use strip():

>>> format_string = "{last}, {first}"
>>> name = {'first': 'John', 'last':''}
>>> format_string.format(**name).strip(', ')
>>> 'John'

answered Jul 5, 2014 at 23:21

Aamir Rind

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3 Comments

derek73 Over a year ago

strip() would remove it from the first version as well ("SmithJohn"), so I'd still need some kind of if structure.

Aamir Rind Over a year ago

No it will not. Have you tested it? Strip only removes leading and trailing characters.

derek73 Over a year ago

No I didn't test it and yes it does work. I guess I forgot strip() only happens at the ends of the string. Thanks.

Kamil Pawłowski · Accepted Answer · 2014-07-05 23:34:40Z

1

You can set value for separator based on condition.

'{first}{separator}{last}'.format(**{"first":first, "last":last,"separator":(", " if last and first else "")})

answered Jul 5, 2014 at 23:34

Kamil Pawłowski

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Comments

johntellsall · Accepted Answer · 2014-07-05 23:13:24Z

0

You could run the original dict through a function to 'clean' it, adding commas where appropriate. Or, have a defaultdict.

The following solution, the simplest, does a post-process step to remove any extra commas and spaces:

source

import re

name = {'first': 'John', 'last':''}
format_string = '{last}, {first}'

def fixme(instr):
    return re.sub('^, ', '',
                  re.sub(', $', '',
                         instr))

print fixme(format_string.format(**dict(first='John', last='')))
print
print fixme(format_string.format(**dict(first='', last='Smith')))

output

John

Smith

answered Jul 5, 2014 at 23:13

johntellsall

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1 Comment

MrAlias Over a year ago

Keep in mind that this solution scales exponentially.

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