Iter

Enable iteration over types in type-level comprehensions.

Quick Example

import typemap_extensions as tm
from typing import Literal

class User:
    name: str
    age: int

# Iterate over attributes in a type alias
type AllNames = tuple[
    m.name for m in tm.Iter[tm.Attrs[User]]
]
# Results in: tuple[Literal["name"], Literal["age"]]

Signature

@_SpecialForm
def Iter(self, tp):
    """Enable iteration over a type."""

What It Does

Iter makes a type iterable in type-level comprehensions. It's used with:

Attrs[T] - Iterate over attributes
Members[T] - Iterate over all members
FromUnion[T] - Iterate over union elements

Usage

With Attrs

# Get all field names
type FieldNames = tuple[
    m.name for m in tm.Iter[tm.Attrs[MyClass]]
]

With Members

# Get all member names (including methods)
type MemberNames = tuple[
    m.name for m in tm.Iter[tm.Members[MyClass]]
]

With FromUnion

type StringUnion = str | int | None

# Iterate over union elements
type UnionTypes = tuple[
    t for t in tm.Iter[tm.FromUnion[StringUnion]]
]

Why Is It Needed?

Python's type system doesn't support iteration by default. Iter is a special form that enables this:

# This doesn't work:
# for m in Attrs[User]: ...

# But this does:
# for m in Iter[Attrs[User]]: ...

Use Cases

Code generation - Generate repetitive code
Type transformations - Apply operations to all members
Metadata extraction - Collect information about types

Note: Iter is mainly used in type aliases, not with eval_typing.

Iter

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