str.format_map() Format with mapping
Last updated: 2026-09-22
str.format_map() Format with mapping
str.format_map(mapping) formats using a mapping object instead of kwargs.
| Category | String Methods |
|---|---|
| Kind | Built-in Type Method |
| Python Version | all |
📝 Syntax
str.format_map(mapping)⚙️ Parameters
| mapping Required | A mapping object supplying field values, like **kwargs. |
|---|
Returns：str. A new string with placeholders filled from the mapping.
Mutates the original：No (returns a new object)
💥 Raises
KeyError— Raised when a placeholder field name is missing from the mapping.ValueError— Raised for an invalid format specifier.
▶ Example
Edit the code, press Run, and see the result in the output panel:
Output：
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❓ FAQ
QWhat is the difference between format_map() and format(**dict)?
Aformat_map() takes the mapping object directly without expanding it into keyword arguments. Combined with a dict subclass (such as one implementing __missing__ like defaultdict), it can supply default values when a key is missing.
QWhat happens when a key does not exist?
AA KeyError is raised. You can return a default value by implementing __missing__ in a custom dict subclass.
QWhat happens when a non-mapping object is passed?
AAn exception is raised (TypeError or AttributeError when the object does not support lookup). The argument must provide field-value lookup capability.
