Zope Size

Common errors

• zope.component.interfaces.ComponentLookupError: No registered adapter for (...) for zope.size.interfaces.ISized

  cause The `get_size` function could not find an adapter that implements `ISized` for the type of object you passed.
  fix You must register an adapter using `zope.component.provideAdapter(YourSizerClass)` before calling `get_size` for objects of that type. Ensure your adapter correctly implements `ISized` and is registered for the correct interface/type.

• AttributeError: 'YourSizerClass' object has no attribute 'size'

  cause Your adapter class implementing `ISized` defines `size` as a regular method or is missing it entirely, instead of a property.
  fix Ensure the `size` attribute in your adapter is defined as a property using the `@property` decorator: ```python @zope.interface.implementer(ISized) class YourSizer: def __init__(self, context): self.context = context @property def size(self): return len(self.context.data) ```

• TypeError: object of type 'YourObject' has no len()

  cause You are likely attempting to use `len()` directly on an object for which `zope.size` is intended, but `len()` is not defined for that object. You should be using `get_size()` with an appropriate adapter.
  fix Instead of `len(my_object)`, ensure you have an `ISized` adapter registered for `my_object`'s type/interface, and then use `get_size(my_object)`.

Warnings

• breaking Version 6.0 dropped support for Python 3.8. Ensure your project is running on Python 3.9 or newer.
  Fix: Upgrade your Python environment to 3.9, 3.10, 3.11, or 3.12. If you must use Python 3.8, pin `zope.size<6.0`.
• gotcha Zope.size relies heavily on `zope.component` for adapter lookup. If no adapter is registered for a given object's type/interface to provide `ISized`, `get_size` will raise a `ComponentLookupError`.
  Fix: Ensure that you have called `zope.component.provideAdapter(YourSizerClass)` for every type you expect to get the size of. This is typically done once at application startup.
• gotcha The `ISized` interface requires a `size` property (not a method). Implementing it as a method instead of a property will lead to `AttributeError` when `get_size` tries to access it, or incorrect behavior.
  Fix: In your adapter implementing `ISized`, ensure `size` is decorated with `@property`: ```python @property def size(self): return ... ```

Install

• pip install zope.size Install latest version

Imports

• ISized

  from zope.size.interfaces import ISized

• get_size

  from zope.size import get_size

Quickstart

This quickstart demonstrates how to define an object, create an adapter that implements `zope.size.interfaces.ISized` for that object's interface, register the adapter using `zope.component.provideAdapter`, and then retrieve the object's size using the `zope.size.get_size` utility function. It highlights the crucial step of adapter registration.

import zope.interface
import zope.component
from zope.size.interfaces import ISized
from zope.size import get_size

# 1. Define an interface for our object
class IMyObject(zope.interface.Interface):
    """An object with some data."""

# 2. Define a class implementing the interface
@zope.interface.implementer(IMyObject)
class MyObject:
    def __init__(self, items):
        self.items = items

# 3. Define an adapter that provides ISized for IMyObject
@zope.component.adapter(IMyObject)
@zope.interface.implementer(ISized)
class MyObjectSizer:
    def __init__(self, context):
        self.context = context

    @property
    def size(self):
        return len(self.context.items)

# 4. Create an instance of our object
my_list_obj = MyObject([1, 2, 3, 4, 5])
my_dict_obj = MyObject({'a': 1, 'b': 2})

# 5. Register the adapter (typically done at application startup)
zope.component.provideAdapter(MyObjectSizer)

# 6. Use get_size to retrieve the size
list_size = get_size(my_list_obj)
dict_size = get_size(my_dict_obj)

# Print the results
print(f"Size of list object: {list_size}")
print(f"Size of dictionary object: {dict_size}")

# Example of an object without a registered adapter
class UnsizedObject: pass
unsized_obj = UnsizedObject()

try:
    get_size(unsized_obj)
except zope.component.interfaces.ComponentLookupError as e:
    print(f"\nError for unsized object (expected): {e}")