Format: KeyError when using curly brackets in strings

Question

I'm running the following code:

asset = {}
asset['abc'] = 'def'
print type(asset)
print asset['abc']
query = '{"abc": "{abc}"}'.format(abc=asset['abc'])
print query

Which throws a KeyError error:

[user@localhost] : ~/Documents/vision/inputs/perma_sniff $ python ~/test.py 
<type 'dict'>
def
Traceback (most recent call last):
  File "/home/user/test.py", line 5, in <module>
    query = '\{"abc": "{abc}"\}'.format(abc=asset['abc'])
KeyError: '"abc"'

Format is obviously getting confused by the wrapping {. How can I make sure format only tries to replace the (correct) inner {abc}.

ie, expected output is:

{"abc": "def"}

(I'm aware I could use the json module for this task, but I want to avoid that. I would much rather use format.)

xnx · Accepted Answer · 2015-08-06 15:26:51Z

41

To insert a literal brace, double it up:

query = '{{"abc": "{abc}"}}'.format(abc=asset['abc'])

(This is documented here, but not highlighted particularly obviously).

answered Aug 6, 2015 at 15:26

xnx

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Comments

Padraic Cunningham · Accepted Answer · 2015-08-06 15:30:10Z

5

wrap the outer braces in braces:

query = '{{"abc": "{abc}"}}'.format(abc=asset['abc'])
print query
{"abc": "def"}

edited Aug 6, 2015 at 15:30

answered Aug 6, 2015 at 15:27

Padraic Cunningham

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2 Comments

tmdavison Over a year ago

think your double close brace is on the wrong one. should be: '{{"abc": "{abc}"}}'

Padraic Cunningham Over a year ago

@tom, yep, typo fixed

bagrat · Accepted Answer · 2015-08-06 15:35:12Z

2

The topmost curly braces are interpreted as a placeholder key inside your string, thus you get the KeyError. You need to escape them like this:

asset = {}
asset['abc'] = 'def'
query = '{{"abc": "{abc}"}}'.format(**asset)

And then:

>>> print query
{"abc": "def"}

answered Aug 6, 2015 at 15:35

bagrat

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