The use of equity screener through Eikon Data APIs is not supported yet. One reason for this is that currently any get_data request is automatically timed out from the server side if the server cannot return the data requested in 15 seconds. Rendering the data through screener can take much longer than 15 seconds to complete, in which case you get back "HTTPError: Backend error. 400 Bad Request". Work is being done to address this issue. Until this work is complete the screener through Eikon Data APIs can only be used for basic expressions that the server can render in less than 15 seconds.

Could you elaborate on what you expect from "detailed documentation on how the instruments field for the get_data function can be specified"? It seems you've already checked the "Eikon Data APIs for Python - Reference Guide" available from the Documentation tab on Eikon Data APIs page on this portal, which provides definition of all the methods and their signatures available in Eikon Data APIs for Python. Per this document the "instruments" argument is a string representing an identifier for a single instrument or a list of strings where each string represents an instrument identifier. For instrument identifier you can use a variety of symbol types including RIC, ISIN, CUSIP, SEDOL, Wertpapierkennnummer, PermID etc. If you have a list of instrument identifiers for which you need market or fundamental & reference data, you can use this list directly to retrieve the data using get_data method, e.g.

ek.get_data(['TRI.N','AAPL.O'],['TR.Revenue'])

The 400 Bad Request error is an HTTP status code indicates that the request you sent to the webserver was malformed , in other words, the data stream sent by the client to the server didn't follow the rules. It means that the request itself has somehow incorrect or corrupted and the server couldn't understand it. There are a number of different causes for a 400: Bad Request Error . It might be a malformed request syntax, invalid request message framing, or deceptive request routing . In most cases, the problem is on the website itself, and there's not much you can do about that.

The "400 Bad Request" error is an HTTP status code that indicates the server cannot process the request due to a client error. This error usually occurs when the server receives an invalid or malformed request from the client.Double-check the URL you're accessing and ensure that it is correct. Additionally, review any parameters or data being sent with the request and verify their format and validity.Ensure that the request follows the proper syntax for the HTTP method being used (e.g., GET, POST, PUT, DELETE). Check that the headers, body, and formatting of the request are correct.