get var returns a value associated with the variable.

set var value binds a variable var to the given value.

add var generator adds a variable var to the environment. If a variable is read before it was defined with the set operation, then a value produces by the generator will be automatically associated with the variable and returned.

del v deletes the variable v from the environment.

The variable v will no longer be bound.

has v evaluates to true if v is bound.

• since 2.1.0

all is a sequence of all variables defined in the environment. Note, the word _defined_ doesn't mean initialized.