CODEWITHSUNDEEP
python
Stephen Rasku
Stephen Rasku

Reputation: 2682

How to expose variable in Python module?

What is the best way to expose a variable from a module?

import otherDBInterface as odbi

def create(host):
    global connection
    global cursor
    connection = odbi.connect(host)
    cursor = connection.cursor()
    ...

I want to expose the cursor variable in the module so I can do something like mydb.cursor.execute("select * from foo;"). I thought using the global keyword would do this but no such luck. cursor is an object so I am not sure how I would declare it so that it would be exposed.

Upvotes: 2

Views: 5148

Answers (2)

Lennart Regebro
Lennart Regebro

Reputation: 172239

Any variable created on a module level is "exposed" by default.

Hence, a module like this will have three exposed variables:

configpath = '$HOME/.config'

class Configuration(object):

    def __init__(self, configpath):
        self.configfile = open(configpath, 'rb')

config = Configuration(configpath)

The variables are configpath, Configuration and config. All of these are importable from other modules. You can also access configs configfile as config.configfile.

You can also have configfile accessible globally this way:

configpath = '$HOME/.config'
configfile = None

class Configuration(object):

    def __init__(self, configpath):
        global configfile
        configfile = open(configpath, 'rb')

config = Configuration(configpath)

But there are various tricky problems with this, as if you get a handle on configfile from another module and it then gets replaced from within Configuration your original handle will not change. Therefore this only works with mutable objects.

In the above example that means that using configfile as a global in this way will not be very useful. However, using config like that could work well.

Upvotes: 2

John
John

Reputation: 13699

You can wrap your connection information in a class

class Database:

    def __init__(self, **kwargs):

        if kwargs.get("connection") is not None:

            self.connection = kwargs["connection"]

        elif kwargs.get("host") is not None:

            self.connection = odbi.connect(host)
            self.cursor = self.connection.cursor()

mydb = Database(host="localhost")

results = mydb.cursor.execute("select * from foo")

#or use it with a connection

mydb = Database(connection="localhost")

results = mydb.cursor.execute("select * from foo")

Upvotes: 5

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