Hi,

I have just read the documentation once again.

The problem is that it specifies that the default value for Dialect.doublequote is True :
<quote>Controls how instances of quotechar appearing inside a field should be themselves be quoted. When True, the character is doubled. When False, the escapechar is used as a prefix to the quotechar. It defaults to True.</quote>

So it is easy to understand that the class csv.Dialect implements this default value. Although the class Dialect default in the csv.reader calling is "Excel" and thus, implicitly, it is csv.excel the default class whose attributes are described in the above paragraph. 

It would be great in this case to describe the attributes of the base class Dialect or specify that all attributes must be settled when we subclass this.

Optionally it would be good that the code of CSV.Dialect be changed for really Boolean values. But the clarification of documentation is more important I think.