CODEWITHSUNDEEP
pythonstring-formatting
Johnny smith
Johnny smith

Reputation: 309

Formatting string which is in double curly braces

I've got following short code I need to execute

isin = 'US0028241000'
payload = f'[{"idType":"ID_ISIN", "idValue": "{isin}"}]'

It outputs a ValueError: Invalid format specifier

I also tried :

payload = '[{"idType":"ID_ISIN", "idValue": "{}"}]'.format(isin)

This one does not work as well. My thought is that it's because the curly braces located within a dict. How can I execute this piece?

Upvotes: 1

Views: 2678

Answers (4)

Narendra Prasath
Narendra Prasath

Reputation: 1531

f string consider whatever inside of the curly braces {} is a python expression.

The problem here also is the same, you are trying to put curly braces as a dictionary but f string considers it as an expression. When it tries to interpret we are getting ValueError: Invalid format specifier.

Example 1: Trying to put list variable inside f string

l = [1,2,3]
`f'{l}'`

Example 2: Trying to put dict inside f string

You should use double curly braces.

`f'[{{"idType":"ID_ISIN", "idValue": "{isin}"}}]'`

But if you declared dict in some variable then you probably will be using as below:

out = {"idType":"ID_ISIN", "idValue": f"{isin}"}
f'{out}'

Upvotes: 1

Abhishek-Saini
Abhishek-Saini

Reputation: 743

isin = 'US0028241000'
payload = f'[{{"idType":"ID_ISIN", "idValue": "{isin}"}}]'
print(payload)

for ignoring any curly braces while formating the string just wrap it with a {}

Upvotes: 1

David Duarte
David Duarte

Reputation: 664

The problem is the curly braces.

To escape them, try:

payload = f'[{{"idType":"ID_ISIN", "idValue": "{isin}"}}]'

Upvotes: 1

chepner
chepner

Reputation: 532093

Your title alludes to the solution. Inside an f-string, you need to use {{ and }} for literal curly braces, but you never introduce them.

>>> f'[{{"idType":"ID_ISIN", "idValue": "{isin}"}}]'
'[{"idType":"ID_ISIN", "idValue": "US0028241000"}]'

That said, don't construct JSON values using string formatting tools; use the json module.

>>> import json
>>> json.dumps([{'idType': 'ID_ISIN', 'idValue': isin}])
'[{"idType": "ID_ISIN", "idValue": "US0028241000"}]'

Upvotes: 3

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