Modify str.format function in python

Question

What str.format does almost exactly I'm looking for. A functionality I would like to add to format() is to use optional keywords and for that I have to use another special character (I guess).

So str.format can do that:

f = "{ID1}_{ID_optional}_{ID2}"
f.format(**{"ID1" : " ojj", "ID2" : "makimaki", "ID_optional" : ""})
# Result: ' ojj__makimaki' #

I can't really use optional ID's. If the dictionary does not contain "ID_optional" it produces KeyError. I think it should be something like this to mark the optional ID:

f = "{ID1}_[IDoptional]_{ID2}"

Another thing: I have lot of template strings to process which are use [] rather than {}. So the best way would be to add the special characters as an argument for the format function.

So the basic question is there a sophisticated way to modify the original function? Or I should write my own format function based on str.format and regular expressions?

See also http://stackoverflow.com/q/28094590/3001761 – jonrsharpe Mar 05 '15 at 14:33 — jonrsharpe, Mar 05 '15 at 14:33

Padraic Cunningham · Answer 1 · 2015-03-05T14:32:59.473

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You if/else and format based on whether the dic has the key or not:

f = "{ID1}_{ID_optional}_{ID2}" if "ID_optional" in d else "{ID1}_{ID2}"

A dict lookup is 0(1) so it is cheap just to check

edited Mar 05 '15 at 14:32

answered Mar 05 '15 at 14:24

Padraic Cunningham

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score 0 · Accepted Answer · answered Mar 05 '15 at 14:27

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One option would be to define your own Formater. You can inherit the standard one and override get_field to return some reasonable default for your use case. See the link for some more documentation.

answered Mar 05 '15 at 14:27

Sorin

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Modify str.format function in python

2 Answers2