Inner function
An inner function is a function defined within the body or scope of another function.
Python How-To
A nested function is a function defined within the body of another function.
- How it is used
- Uses inner functions to create callable variants with fixed values and to wrap functions in decorators.
- How deep it goes
- Works through returned functions, enclosing-variable assignment, and decorator wrapper pitfalls; defers a full explanation of closures.
- Examples
- Shows incrementing functions, a decorator wrapper, metadata checks, and contrasting assignments with and without nonlocal.
- What you can do after
- Build it from scratch: return an inner function that uses an enclosing value, or use nonlocal when it must change that value.
F# in Action: A Revised Edition of Get Programming with F#
A nested function is a function defined inside another scope or function.
- How it is used
- Uses inner functions to keep small helper logic private to a larger operation.
- How deep it goes
- Defines nested functions and capturing, while only noting performance implications without further detail.
- Examples
- Demonstrates a local `makeFullName` helper that builds a greeting from first and last names.
- What you can do after
- Apply inner functions to place helper behavior beside the operation that uses it.
Read how F# in Action: A Revised Edition of Get Programming with F# explains inner function →
Get Programming: Learn to code with Python
A function defined within the scope of an enclosing function.
- How it is used
- Explains how to organize task-specific helpers and create specialized functions within an enclosing function.
- How deep it goes
- Defines nesting, scope, returned function objects, and chained execution through small examples and trace exercises.
- Examples
- Uses singing stops, chained message functions, area helpers, student vacation details, and file-data analysis helpers.
- What you can do after
- Build it from scratch by defining task-specific inner functions, calling them within scope, and returning function objects when useful.
Read how Get Programming: Learn to code with Python explains inner function →
Python Workout, Second Edition
An inner function is a function defined within the scope of another function or enclosing code block.
- How it is used
- Uses inner functions to generate multiple specialized password functions from different character strings.
- How deep it goes
- Explains definition timing, returned functions, enclosing-scope access, and LEGB lookup, but stops short of broader closure mechanics.
- Examples
- Demonstrates password generators for alphabetic and symbol character sets, with lengths five and ten.
- What you can do after
- Build it from scratch: define, return, and invoke specialized password generators that retain an outer character set.
Read how Python Workout, Second Edition explains inner function →
Python Workout: 50 ten-minute exercises
An inner function is a function defined within the body of another function.
- How it is used
- Uses inner functions to create reusable password generators with different character restrictions.
- How deep it goes
- Explains definition, creation timing, returned functions, closures, and LEGB lookup, stopping short of broader closure mechanics.
- Examples
- Demonstrates password generators for alphabetic and symbolic character sets, including multiple returned functions and generated outputs.
- What you can do after
- Build reusable function factories that retain configuration from an outer call.
Read how Python Workout: 50 ten-minute exercises explains inner function →
Related concepts
- functionkind of · A function is a callable program unit that performs an operation, may accept inputs, and can produce a result or side effect.
- closureequivalent to · A closure is a function or callable value together with access to bindings from the lexical environment in which it was created.
- enclosing functionpart of · An enclosing function is a function whose body contains a nested function definition and provides a surrounding lexical scope for it.
- scopeuses · Scope is the region of a program in which names are visible and can be resolved according to the language’s lookup rules.
- bindinguses · Name binding is the association of an identifier with the program entity or value it denotes.
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