CODEWITHSUNDEEP
pythonpython-3.x
Ruben
Ruben

Reputation: 309

How can i import class from another file in python?

i'm a newbee at python and i'm having this error when importing class from a file this is my directory

-*
-- access.py
-- alloweds.py

in my acces.py i have this (is not all the complete code)

from alloweds import clasifier, record_user
conn = MySQLdb.connect(host='localhost', user='root', passwd='', db='python')
cursor=conn.cursor()

uuid_id = uuid.uuid1()
alloweds=clasifier()
record = record_user()

and in my alloweds.py

from access import cursor

class clasifier():

    def __init__(self):
        self.Invited=['Test']

    def verify(self,name):        
        if name in self.Invited:
            return('Accept')
        else:
            return('Deny')


class record_user():
 ##code

and this is the error log

Traceback (most recent call last):
  File ".\access.py", line 9, in <module>
    from listaPermitidos import clasifier, record_user
  File "C:\Users\rbnvl\alloweds.py", line 3, in <module>
    from access import cursor
  File "C:\Users\rbnvl\access.py", line 9, in <module>
    from alloweds import clasifier, record_user
ImportError: cannot import name 'clasifier' from 'alloweds' (C:\Users\rbnvl\alloweds.py)

Upvotes: 1

Views: 1457

Answers (5)

bruno desthuilliers
bruno desthuilliers

Reputation: 77892

As already mentionned, your issue comes from a circular dependencie - both modules depend on each other - which is both a general design issue (you should not have circular dependencies, whatever the language used) and badly supported by Python.

While there are quick'n'dirty technical workarounds those only mask the symptom, they don't cure the issue itself. There are various strategies to avoid circular dependencies (like extracting the common dependency to a distinct module as in ex4's answer), and most often you use a combination of thise. In your case, the very obvious issue is that you make your allowed module dependent on a global cursor for no good reason. What you should do here is, plain simply, to explicitely pass the dependee as argument to the depender ie:

class Depender():
    def __init__(self, dependee):
        self.dependee = dependee

    def dothis(self, arg):
        return self.dependee.do_something_with(arg)

This strategy (named "dependency injection") not only breaks the circular dependency, but also makes your code much more easily testable in isolation.

Now there's another - unrelated but severe - issue with your code: your allowed module's code should not depend on a cursor but on the connection object itself. The first and main reason is that cursors are not reentrant so if one function uses the cursor to iterate over a select query issue, and during the iteration calls another function that uses the same cursor for any other operation, you'll get very unexpected results. Also, you'll still need the connection object to handle transactions. Database connections are costly, but cursors are cheap disposable objects, so there's no good reason to try and reuse a cursor.

Upvotes: 1

ex4
ex4

Reputation: 2428

That is circular depency. Create one more file, for example database.py where you import your cursor.

# database.py
conn = MySQLdb.connect(host='localhost', user='root', passwd='', db='python')
cursor=conn.cursor()

# alloweds.py
from database import cursor
...

# access.py
from alloweds import clasifier, record_user
from database import cursor
...

Upvotes: 2

Jacob Fullerton
Jacob Fullerton

Reputation: 54

You have a loop when you are importing from both files. So if you have only 1 file import from the other you should be fine.

Upvotes: 1

lone_ranger
lone_ranger

Reputation: 75

You cannot import two files vice versa, like, from class1 import Class1 in script 2 and from class2 import Class2 in script 1.

Upvotes: -2

Avishka Balasuriya
Avishka Balasuriya

Reputation: 31

In youe access.py try,

from alloweds.classifier import classifier
from alloweds.recode_user import recode_user

This works if the both file in same directory. but if those are in different directories it will not work. If you want to import classes from different level of directories you have to import them through main.py

Upvotes: -1

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