Context

TODO

Context classes

class caterpillar.context.Context

Represents a context object with attribute-style access.

class caterpillar.context.ContextPath(path: str = None)

Represents a lambda function for retrieving a value from a Context based on a specified path.

class caterpillar.context.ContextLength(path: ContextPath)

class caterpillar.context.ConditionContext(condition: _ContextLambda | bool, depth=2)

Class implementation of an inline condition.

Use this class to automatically apply a condition to multiple field definitions. Note that this class will only work if it has access to the parent stack frame.

@struct
class Format:
    magic: b"MGK"
    length: uint32

    with this.length > 32:
        # other field definitions here
        foo: uint8

This class will replace any existing fields!

Parameters:

condition (Union[_ContextLambda, bool]) – a context lambda or constant boolean value

Special paths

context.this

Represents a lambda function for retrieving a value from a Context based on a specified path.

context.ctx

Represents a lambda function for retrieving a value from a Context based on a specified path.

context.parent

Represents a lambda function for retrieving a value from a Context based on a specified path.

Special Attributes

context.CTX_PARENT = '_parent'

context.CTX_OBJECT = '_obj'

context.CTX_OFFSETS = '_offsets'

context.CTX_STREAM = '_io'

context.CTX_FIELD = '_field'

context.CTX_VALUE = '_value'

context.CTX_POS = '_pos'

context.CTX_INDEX = '_index'

context.CTX_PATH = '_path'

context.CTX_SEQ = '_is_seq'

Expressions

class caterpillar.context.ExprMixin

A mixin class providing methods for creating binary and unary expressions.

class caterpillar.context.BinaryExpression(operand: Callable[[Any, Any], Any], left: Any | _ContextLambda, right: Any | _ContextLambda)

Represents a binary expression.

Parameters:

• operand – The binary operator function.

• left – The left operand.

• right – The right operand.

class caterpillar.context.UnaryExpression(name: str, operand: Callable[[Any], Any], value: Any | _ContextLambda)

Represents a unary expression.

Parameters:

• name – The name of the unary operator.

• operand – The unary operator function.

• value – The operand.