在 Python 3.8 中使用 qPython 和 Pandas 在 q-lang 中查询

Question

I am totally new to q-language, but I need to use it in order to access a kdb server to get the data from.

I am using Python 3.8, under Windows10, with qPython installed.

I have trouble getting the query to the server.

from qpython import qconnection
import pandas as pd


tbl = 'q("h\"select from trade where date = 2007.02.28, sym = `XXXX\"")'


q = qconnection.QConnection(host=server, port=server_port, username=user, password=server_password, timeout=server_timeout)

q.open()
df = pd.DataFrame(q.sendSync('tbl'))
q.close()

On executing the script it returns an error at line 15:

qpython.qtype.QException: b'tbl'

So I have a trouble sending the correct expression to the server. I was able to pass the expression via terminal, using q (with PyQ) under Linux Debian 10, so the query is correct.

(The server details are skipped, as well as the bond name).

Answer 1

PyQ and qPython are being confused here. q.sendSync('tbl') will get the variable tbl from the kdb server. This error: qpython.qtype.QException: b'tbl' means tbl doesn't exist on the kdb server. I think what you wanted is the select statement to be sent to the kdb server:

from qpython import qconnection
import pandas as pd

q = qconnection.QConnection(host=server, port=server_port, username=user, password=server_password, timeout=server_timeout, pandas=True)

q.open()
df = q.sendSync('select from trade where date = 2007.02.28, sym = `XXXX')
q.close()

It might be worth while for you to spend sometime with q itself and get up to speed with some basics here:

https://code.kx.com/q4m3/1_Q_Shock_and_Awe/