string.format() with optional placeholders

Question

I have the following Python code (I'm using Python 2.7.X):

my_csv = '{first},{middle},{last}' print( my_csv.format( first='John', last='Doe' ) ) 

I get a KeyError exception because 'middle' is not specified (this is expected). However, I want all of those placeholders to be optional. If those named parameters are not specified, I expect the placeholders to be removed. So the string printed above should be:

John,,Doe 

Is there built in functionality to make those placeholders optional, or is some more in depth work required? If the latter, if someone could show me the most simple solution I'd appreciate it!

Answer 1

Here is one option:

from collections import defaultdict  my_csv = '{d[first]},{d[middle]},{d[last]}' print( my_csv.format( d=defaultdict(str, first='John', last='Doe') ) ) 

Answer 2

"It does{cond} contain the the thing.".format(cond="" if condition else " not") 

Thought I'd add this because it's been a feature since the question was asked, the question still pops up early in google results, and this method is built directly into the python syntax (no imports or custom classes required). It's a simple shortcut conditional statement. They're intuitive to read (when kept simple) and it's often helpful that they short-circuit.