Utility Classes :: Length

Overview

The Length() class is used when you don't care about the type of a sequence, or its contents, only its length.

The Length() constructor takes a single argument, the desired sequence length. If the object being checked is not a sequence, or of the wrong length, things will blow up.

The following signature asserts that the sole parameter is a sequence -- regardless of type -- containing eight elements:

@accepts(Length(8))

Details

• The Length() constructor takes a single argument. If more or fewer arguments are provided, a TypeCheckError will be raised.

  The value to this argument will be used to specify the length of a sequence, and accordingly needs to be something that can be passed to the built-in int() function.

• If the object being checked does not define a __len__ method, a _TC_TypeError will be raised.

  It is expected that this exception will be caught and converted to a TypeCheckError before it reaches the user.

• If the sequence being checked is of the wrong length, a _TC_LengthError will be raised.

  It is expected that this exception will be caught and converted to a TypeCheckError before it reaches the user.

• Length instances that were created with the same length parameter will compare (==) as equals.

  All instances that compare equal will also hash to the same value.