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docs: add note about unmatched braces in format strings #1031

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c969983
docs: add note about unmatched braces in format strings
devimano2011 Apr 29, 2026
88748f2
Handle ValueError during string forfix: catch ValueError in _check_an…
devimano2011 May 2, 2026
cfe3785
docs: fix trailing whitespace and improve unmatched brace NOTE with c…
devimano2011 May 2, 2026
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10 changes: 9 additions & 1 deletion docs/source/basics.md
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Original file line number Diff line number Diff line change
Expand Up @@ -204,9 +204,17 @@ request:
graphql_query: "{%raw%}{{ user(id: 123) {{ first_name }} }}{%endraw%}"
```

**NOTE**: This is a toy example, if you want to use GraphQL with tavern then
**NOTE**: This is a toy example, if you want to use GraphQL with tavern then
head over to the [GraphQL docs](./graphql.md).

**NOTE**: If a string value contains an unmatched `{` that is not a valid
format placeholder, Tavern will log a warning and pass the string through
unformatted rather than raising an error. For example, an MQTT payload value
like `{Explanation 1` would be passed through unchanged (logged as a warning),
whereas `{{Explanation 1}}` would be formatted to the literal string
`{Explanation 1}`. To avoid unexpected behaviour, always escape literal curly
braces as `{{` and `}}` as described above.

Since `0.5.0`, Tavern also has some 'magic' variables available in the `tavern`
key for formatting.

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10 changes: 9 additions & 1 deletion tavern/_core/dict_util.py
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Expand Up @@ -70,7 +70,15 @@ def _check_and_format_values(to_format: str, box_vars: Box) -> str:
type(would_replace),
)

return to_format.format(**box_vars)
try:
return to_format.format(**box_vars)
except ValueError as e:
logger.warning(
"Failed to format string '%s': %s - passing through unformatted",
to_format,
e,
)
return to_format


def _attempt_find_include(to_format: str, box_vars: box.Box) -> str | None:
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