Adding new StringFormat node

[Pauan]

This PR adds in a new StringFormat node that just uses Python's string format method.

Similar to the MathExpression node, it supports a maximum of 26 different arguments (a-z).

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The Python string format method is very useful:

• It can be used as an easy way to concatenate strings.
• It can be used to convert anything into a string.
• It can format items with padding and alignment.
• It can format numbers with zero-padding.
• It can format numbers with a specific number of decimals.
• And more!

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

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Reviewing files that changed from the base of the PR and between 1e8fcd5 and f0a5774.

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• comfy_extras/nodes_string.py

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📝 Walkthrough

Walkthrough

This PR adds a new StringFormat node to the string utilities module. The node accepts an autogrowing mapping values (lowercase keys) and an f_string template, executes by calling f_string.format(**values) and returning a NodeOutput, and is registered in StringExtension.get_node_list() so it is available to the node registry.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'Adding new StringFormat node' clearly and concisely describes the main change in the pull request, which is the addition of a new StringFormat node to the codebase.
Description check	✅ Passed	The description is directly related to the changeset, explaining what the StringFormat node does, its capabilities, and use cases for Python's string format method.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[coderabbitai]

Actionable comments posted: 1

🧹 Nitpick comments (1)

comfy_extras/nodes_string.py (1)

33-36: ⚡ Quick win

Consider adding error handling for format exceptions.

The str.format() method can raise KeyError (missing key in template) or ValueError (invalid format specifier) for malformed format strings. Other nodes in this file (RegexMatch, RegexExtract, JsonExtractString) catch expected exceptions and return safe defaults, providing better user experience.

Consider wrapping the format call in a try-except block to handle format errors gracefully.

♻️ Proposed error handling

     `@classmethod`
     def execute(
         cls, values: io.Autogrow.Type, f_string: str
     ) -> io.NodeOutput:
-        return io.NodeOutput(f_string.format(**values))
+        try:
+            return io.NodeOutput(f_string.format(**values))
+        except (KeyError, ValueError) as e:
+            return io.NodeOutput(f"Format error: {str(e)}")

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@comfy_extras/nodes_string.py` around lines 33 - 36, The execute method in the
class (execute in comfy_extras/nodes_string.py) calls f_string.format(**values)
without guarding against formatting errors; wrap that call in a try/except that
catches KeyError and ValueError (and optionally Exception) and return a safe
default via io.NodeOutput (e.g., empty string or the original template) on
error, and log or include the error message if appropriate so behavior matches
other nodes like RegexMatch/RegexExtract/JsonExtractString.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@comfy_extras/nodes_string.py`:
- Around line 12-25: The autogrow template (io.Autogrow.TemplateNames used for
the "values" input) sets min=0 but the default f_string is "{a}", which can
KeyError when no parameters exist; update either autogrow to require at least
one parameter by changing min from 0 to 1, or make the default f_string safe
(e.g., set default to an empty string "") so the node_id "StringFormat" / input
"f_string" no longer references a missing parameter—choose and apply one of
these fixes consistently in the Schema definition.

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Nitpick comments:
In `@comfy_extras/nodes_string.py`:
- Around line 33-36: The execute method in the class (execute in
comfy_extras/nodes_string.py) calls f_string.format(**values) without guarding
against formatting errors; wrap that call in a try/except that catches KeyError
and ValueError (and optionally Exception) and return a safe default via
io.NodeOutput (e.g., empty string or the original template) on error, and log or
include the error message if appropriate so behavior matches other nodes like
RegexMatch/RegexExtract/JsonExtractString.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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📥 Commits

Reviewing files that changed from the base of the PR and between 6887165 and 1e8fcd5.

📒 Files selected for processing (1)

• comfy_extras/nodes_string.py

[alexisrolland]

Tested and it works fine.