I know that I pushed this topic 3 years ago and a number of people piped in that it was a good idea. Lets try once again to press this forward.
REMOVED SPECIFIC USE CASES AS IT WAS DISTRACTING
EDITED TO REMOVE A MUTILATION FROM C API TO PYTHON
EDITED TO REMOVE MUTILATION TO THE PROPOSAL INTRODUCT IN AI CLEANUP PASS BY ROLLING BACK TO EARLIER DRAFT
PEP: XXXX
Title: Lazy-Loading Strings for Improved Efficiency in Python
Author: [Your Name]
Status: Draft
Type: Standards Track
Created: YYYY-MM-DD
Python-Version: TBD
Abstract
This PEP proposes the introduction of lazy-loading strings in Python by
extending the existing PyUnicodeObject
structure. Lazy-loading allows strings
to be initialized with a loader function that defers their full construction
until explicitly accessed. This feature improves memory efficiency and reduces
initialization costs for applications that handle large strings conditionally.
Lazy-loaded strings behave identically to regular Python strings once evaluated,
ensuring seamless integration with Python’s str
type and string-related
operations.
Motivation
Lazy-loaded strings provide a mechanism to defer the initialization of string
data until explicitly accessed. This is particularly valuable in scenarios where
memory usage and performance are critical, such as:
- Language bridges that pass strings between environments.
- GUI toolkits with conditionally displayed dynamic content.
- Large-scale data processing with sparsely accessed strings.
- Web applications generating dynamic responses.
- Machine learning pipelines with text-heavy datasets.
By introducing lazy-loaded strings, Python can offer developers an efficient way
to handle string-heavy workloads without unnecessary overhead.
Potential Python modules that could benefit from lazy loading is any kit for which Python strings are immutable and can have pass through semantics. These include Java bindings(JPype, PyJNIus, Chaquopy), C# bind (Pythonnet) ObjC binds, GUI kits (Qt), and other potential pass through libraries.
Specification
Overview
Lazy-loaded strings are a new type of string object that defers the computation
or loading of its value until accessed. They improve performance and memory
efficiency when working with external libraries or systems requiring deferred
string evaluation.
API Definition
A new API will be introduced to create lazy-loaded strings:
.. code-block:: C
PyObject* PyUnicode_FromLazyLoader(PyObject* loader) {
/*
* Creates a lazy-loaded string from a loader function.
*
* Parameters:
* loader: Is a Python proxy object which implements the ``__str__`` interface which
* will produce a string when needed.
*
* Returns:
* A PyObject representing a lazy-loaded string that defers evaluation
* until accessed, or NULL if an error occurs.
*/
}
Key Points:
- Loader Function:
- The
loader
parameter is a callable that takes no arguments and returns
a string. - The loader function is invoked only when the lazy-loaded string is accessed
for the first time.
- The
- Return Type:
- The returned object is a lazy-loaded string, which behaves identically to a
regular Python string once evaluated.
- The returned object is a lazy-loaded string, which behaves identically to a
Points to consider: We may need to use something other than __str__
unless the representation is already knowable at creation time. We are to fill out the contents and not mutilate the other fields of the representation. Consider adding a representation enum so that memory model can be defined at creation time.
Behavior
Lazy-loaded strings exhibit the following behaviors:
- Deferred Evaluation:
- The loader function is not invoked until the string is accessed (e.g., via
str()
,len()
, slicing, or string methods). - Until evaluation, the lazy-loaded string occupies minimal memory, storing
only the loader function.
- The loader function is not invoked until the string is accessed (e.g., via
- String Operations:
- Lazy-loaded strings support all standard string operations (
len()
,
slicing, concatenation, etc.). - Accessing or using a lazy-loaded string triggers evaluation, after which it
behaves like a regular string.
- Lazy-loaded strings support all standard string operations (
- Caching:
- Once evaluated, the string value is cached within the lazy-loaded string
object for subsequent access. - The loader function is not invoked again.
- Once evaluated, the string value is cached within the lazy-loaded string
- Error Handling:
- If the loader function raises an exception during evaluation, the lazy-
loaded string becomes invalid, and subsequent access will raise the same
exception.
- If the loader function raises an exception during evaluation, the lazy-
Edge Cases
- Never Accessed:
- If a lazy-loaded string is created but never accessed, the loader function
is never invoked, and no string value is computed.
- If a lazy-loaded string is created but never accessed, the loader function
- Thread Safety:
- Lazy-loaded strings ensure thread-safe evaluation by locking the loader
function during the first access. This prevents race conditions when the
string is accessed concurrently.
- Lazy-loaded strings ensure thread-safe evaluation by locking the loader
- Compatibility:
- Lazy-loaded strings are fully compatible with Python’s existing string APIs
and modules. No changes are required in existing modules to support lazy-
loaded strings.
- Lazy-loaded strings are fully compatible with Python’s existing string APIs
Implementation Details
Lazy-loaded strings will be implemented as a new type within CPython, extending
the PyUnicode
type. The following changes will be made:
-
Modify Internal Type:
- A modify existings internal type,
PyUnicode
, to include fields need for loading. - This type will store:
- A reference to the loader function (PyObject*) which will add relevant contents in
an agreed upon representation (8, 16 or 32 bit) - A flag indicating whether the string has been evaluated.
- The cached string value (if evaluated) as the pointer to the outside memory.
- A reference to the loader function (PyObject*) which will add relevant contents in
- A modify existings internal type,
-
Evaluation Logic:
- When any string operation is performed a macro will check the string represention for null and if it is missing consult the loader to fetch the string.
The resulting value is cached. tp_repr
should not lazy load to avoid potential conflicts with debugging instead it will give<lazy string %s>
where %s is the loader type.
- When any string operation is performed a macro will check the string represention for null and if it is missing consult the loader to fetch the string.
-
Integration:
- Lazy-loaded strings will seamlessly integrate with Python’s existing string
handling mechanisms. - No changes will be made to existing modules or APIs.
- Lazy-loaded strings will seamlessly integrate with Python’s existing string
Output:
.. code-block:: text
Before access
Evaluating string...
12
After access
Output:
.. code-block:: text
Error: Failed to load string!
Performance Considerations
Lazy-loaded strings reduce memory usage and improve performance by deferring
string evaluation until needed. Benchmarks will measure:
- Memory usage reduction in scenarios involving large strings.
- Performance improvements when interacting with external libraries requiring
deferred evaluation.
Preliminary tests suggest a significant reduction in memory usage for workloads
involving large strings, such as log processing tools or machine learning
pipelines.
Security Considerations
Lazy-loaded strings do not introduce new security risks, as they rely on user-
provided loader functions. Developers must ensure that the loader function is
safe and does not execute malicious code. Additionally, thread safety is ensured
during evaluation to prevent race conditions.
Backward Compatibility
This proposal does not require changes to existing modules or APIs. Lazy-loaded
strings are fully compatible with Python’s str
type and string-related
operations. Existing codebases will not be affected by this feature.
Open Questions
- Features:
- Should lazy-loaded strings support additional features, such as lazy-loaded
bytes or other types?
- Should lazy-loaded strings support additional features, such as lazy-loaded
- GC Interactions:
- How should lazy-loaded strings interact with garbage collection, especially
when the loader function holds references to external resources?
- How should lazy-loaded strings interact with garbage collection, especially
- Performance Impact:
- What is the overhead of checking for an additional flag during string
operations, and how can it be minimized?
- What is the overhead of checking for an additional flag during string