为什么在以下代码中我得到了不同的编码方式?
>>> require 'stringio'
>>> a = StringIO.new('toto')
>>> a.read(2).encoding
=> #<Encoding:ASCII-8BIT>
>>> a.read.encoding
=> #<Encoding:UTF-8>
>>> a.read.encoding
=> #<Encoding:ASCII-8BIT>