How to connect Python to Db2

Question

The documentation is difficult to find, and once you find it, it’s pretty abysmal. Here’s what I’ve found over the past 3 hours.

You need to install ibm_db using pip, as follows:

pip install ibm_db

You’ll want to create a connection object. The documentation is here.

Here’s what I wrote:

from ibm_db import connect
# Careful with the punctuation here - we have 3 arguments.
# The first is a big string with semicolons in it.
# (Strings separated by only whitespace, newlines included,
#  are automatically joined together, in case you didn't know.)
# The last two are emptry strings.
connection = connect('DATABASE=<database name>;'
                     'HOSTNAME=<database ip>;'  # 127.0.0.1 or localhost works if it's local
                     'PORT=<database port>;'
                     'PROTOCOL=TCPIP;'
                     'UID=<database username>;'
                     'PWD=<username password>;', '', '')

Next you should know that commands to ibm_db never actually give you results. Instead, you need to call one of the fetch methods on the command, repeatedly, to get the results. I wrote this helper function to deal with that.

def results(command):
    from ibm_db import fetch_assoc

    ret = []
    result = fetch_assoc(command)
    while result:
        # This builds a list in memory. Theoretically, if there's a lot of rows,
        # we could run out of memory. In practice, I've never had that happen.
        # If it's ever a problem, you could use
        #     yield result
        # Then this function would become a generator. You lose the ability to access
        # results by index or slice them or whatever, but you retain
        # the ability to iterate on them.
        ret.append(result)
        result = fetch_assoc(command)
    return ret  # Ditch this line if you choose to use a generator.

Now with that helper function defined, you can easily do something like get the information on all the tables in your database with the following:

from ibm_db import tables

t = results(tables(connection))

If you’d like to see everything in a given table, you could do something like this now:

from ibm_db import exec_immediate

sql="LIST * FROM " + t[170]['TABLE_NAME']  # Using our list of tables t from before...
rows = results(exec_immediate(connection, sql))

And now rows contains a list of rows from the 170th table in your database, where every row contains a dict of column name: value.

Hope this all helps.

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