Evaluate Python expression {expr} and return its result converted to Vim data structures. Numbers and strings are returned as they are (strings are copied though, Unicode strings are additionally converted to 'encoding'). Lists are represented as Vim |List| type. Dictionaries are represented as Vim |Dictionary| type with keys converted to strings. Can also be used as a |method|: GetExpr()->py3eval() {only available when compiled with the |+python3| feature}