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11.20.6 ProtocolError Objects

A `ProtocolError` object describes a protocol error in the underlying transport layer (such as a 404 `not found' error if the server named by the URI does not exist). It has the following members:

`url`
  The URI or URL that triggered the error.

`errcode`
  The error code.

`errmsg`
  The error message or diagnostic string.

`headers`
  A string containing the headers of the HTTP/HTTPS request that triggered the error.