eval_typing

The main function to evaluate types at runtime.

Quick Example

from typemap import eval_typing
import typemap_extensions as tm

class User:
    name: str
    age: int

result = eval_typing(tm.KeyOf[User])
# Returns: tuple[Literal["name"], Literal["age"]]

Signature

def eval_typing(type_expr: Any) -> Any:
    """Evaluate a type expression and return the resolved type."""

What It Does

eval_typing takes a type expression and:

Resolves any type aliases
Applies type operators (like KeyOf, Partial)
Evaluates special forms (like IsAssignable)
Returns the concrete type

Usage

Basic Type

class MyClass:
    x: int
    y: str

result = eval_typing(MyClass)
# Returns the class itself

With Type Operators

# Get all field names
keys = eval_typing(tm.KeyOf[User])

# Make fields optional
partial = eval_typing(tm.Partial[User])

# Pick specific fields
picked = eval_typing(tm.Pick[User, tuple["name"]])

With Special Forms

# Check type compatibility
is_compatible = eval_typing(tm.IsAssignable[int, float])
# Returns: True

Error Handling

from typemap.type_eval import TypeMapError, StuckException

try:
    result = eval_typing(some_type)
except TypeMapError as e:
    print(f"Type error: {e}")
except StuckException as e:
    print(f"Can't evaluate: {e}")

When to Use

Use eval_typing when you need to:

Get information about a type at runtime
Transform types dynamically
Build things based on type metadata

Tip: For most use cases, you'll use eval_typing combined with type operators from typemap_extensions.

eval_typing

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