FrozenList

1.8.0 verified Tue May 12 auth: no python install: verified quickstart: verified

FrozenList is a Python library providing a list-like structure that implements collections.abc.MutableSequence. The list remains mutable until the freeze() method is called, after which any modifications raise a RuntimeError. The current version is 1.8.0, released in October 2025, with a release cadence of approximately one to two updates per year.

pip install frozenlist

Common errors

error ModuleNotFoundError: No module named 'frozenlist' ↓

cause The 'frozenlist' package has not been installed in the Python environment you are using.

fix

Install the package using pip: pip install frozenlist

error RuntimeError: Cannot modify frozen list. ↓

cause You attempted to modify a FrozenList instance after its `freeze()` method has been called, rendering it immutable.

fix

Ensure modifications are made before calling freeze(), or create a new FrozenList instance if further modifications are required.

error ERROR: Could not build wheels for frozenlist, which is required to install pyproject.toml-based projects. ↓

cause This error typically occurs during installation, often when Python cannot compile the underlying C extensions of 'frozenlist', sometimes due to missing build tools (like `gcc`) or compatibility issues with newer Python versions (e.g., Python 3.11, 3.12) that might require a more recent 'frozenlist' version or specific compiler flags.

fix

Ensure your build tools (like gcc) are installed and up-to-date. If using a newer Python version, try upgrading pip and setuptools (pip install --upgrade pip setuptools) or check if a newer 'frozenlist' version with pre-built wheels for your Python version is available.

Warnings

breaking Dropped support for Python 3.7 in version 1.4.0. ↓

fix Upgrade your Python environment to version 3.8 or newer.

breaking Dropped support for Python 3.6 in version 1.3.0. ↓

fix Upgrade your Python environment to version 3.7 or newer.

gotcha Attempting to modify a FrozenList after calling freeze() raises a RuntimeError. ↓

fix Ensure that all necessary modifications are made before freezing the list.

gotcha A FrozenList instance is hashable only when frozen; attempting to hash a non-frozen instance raises a RuntimeError. ↓

fix Call freeze() before attempting to hash a FrozenList instance.

Install compatibility verified last tested: 2026-05-12

python os / libc status wheel install import disk

3.10 alpine (musl) - - 0.00s 18.3M

3.10 slim (glibc) - - 0.00s 19M

3.11 alpine (musl) - - 0.00s 20.2M

3.11 slim (glibc) - - 0.00s 21M

3.12 alpine (musl) - - 0.00s 12.1M

3.12 slim (glibc) - - 0.00s 13M

3.13 alpine (musl) - - 0.00s 11.7M

3.13 slim (glibc) - - 0.01s 12M

3.9 alpine (musl) - - 0.00s 17.8M

3.9 slim (glibc) - - 0.01s 18M

Imports

FrozenList
```
from frozenlist import FrozenList
```

Quickstart verified last tested: 2026-04-23

Demonstrates creating a FrozenList, modifying it, freezing it, and handling attempts to modify it after freezing.

from frozenlist import FrozenList

# Create a mutable FrozenList
fl = FrozenList([1, 2, 3])
fl.append(4)
print(fl)  # Output: [1, 2, 3, 4]

# Freeze the list
fl.freeze()

# Attempting to modify the frozen list raises RuntimeError
try:
    fl.append(5)
except RuntimeError as e:
    print(e)  # Output: Cannot modify frozen list.