The Directory API is built on HTTP and JSON, so any standard HTTP client can send requests to it and parse the responses.
However, the Google APIs client libraries provide better language integration, improved security, and support for making calls that require user authorization. The client libraries are available in a number of programming languages; by using them you can avoid the need to manually set up HTTP requests and parse the responses.
|Google APIs Client Library for Python||PyDoc|
|Google APIs Client Library for Java||Javadoc|
|Google APIs Client Library for .NET||Reference documentation|