Inheritance

[Nancy]

I'm experimenting with inheritance and could use some guidance.

Here's what I have, after fighting off error messages on previous attempts. :-)

import ftplib
class myftp(ftplib.FTP):
    def __init__(self):
        self.FTP = ftplib.FTP()   

This appears to do what I want it to do* (see below).
But should I be setting it up differently than shown above?

*As an example, I can do the following and it works.

ftp = myftp()
ftp.connect(host)
ftp.login(user, passwd)
# etc
ftp.close()

Thanks for any input, thanks!
-Nancy

[Jay Wren]

That works, but you are allocating and initializing the FTP member and never using it.

import ftplib

class myftplib(ftplib.FTP):

    def __init__(self):

        pass

would work just the same, and for that matter, so would:

class myftplib(ftplib.FTP):

  pass

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[Ryan Burns]

If you wanted to pass some of your own arguments to your own init and also use the original init you can also do that:

import ftplib

class MyFTPLib(ftplib.FTP):

   def __init__(self,custom,host):

      ftplib.FTP.__init__(self,host)

      self.custom = custom

This stackoverflow thread has some more discussion about this kind of thing:

http://stackoverflow.com/questions/576169/understanding-python-super-and-init-methods

I'm sure you can also take a variable number of arguments to match the FTP init precisely, I think you would say something like *args and then pass that to the FTP init?

- As an aside, the Python style guide recommends using CapWords for class names.

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[Paul Woolcock]

It would be better to use `super` instead:

    import ftplib
    class MyFTP(ftplib.FTP):
        def __init__(self):
            super(MyFTP, self).__init__()

Here is the python documentation on `super`: http://docs.python.org/library/functions.html?highlight=super#super

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[Nancy]

 

I appreciate the feedback! So far, now, I have:

 

import ftplib
class MyFTP(ftplib.FTP):
    def __init__(self):

        pass

 

I do plan to do some "custom" but am not there yet :)

 

I did try this (in place of "pass"):  super(MyFTP, self).__init__()

TypeError: super() argument 1 must be type, not classobj

 

Thanks again,

-Nancy

 

[Nancy]

Also I should have mentioned (though don't think it's been a factor yet):

Py 2.6 on Win

-Nancy

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[Ryan Burns]

I tried this exact code;

import ftplib

class MyFTP(ftplib.FTP):

    def __init__(self):

        super(MyFTP,self).__init__()

    

And it didn't throw any errors.  A quick google indicated this error can occur if the parent class you are inheriting from is not a new-style class.  I'm not sure why that would be the case in your case, although I am on 2.7.  

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[Ryan Burns]

Ahaha, the ftplib.FTP class is an old style class in the 2.6 release.

Huh, I checked both the 2.6.8 and 2.7.3 ftplib source and it's an old style class in both.  I'm not sure why it worked for me.

You can still use ftplib.FTP.__init__(self)      - super() only really matters if you have multiple inheritance (feel free to disabuse me of that notion if it's not the case).

-Ryan

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[Ryan Burns]

Oh, it worked for me because I didn't create an instance of MyFTP when I tested it, and that is of course when the error occurs.

Long story short: you can't use super() if you're inheriting from ftplib.FTP in that version of Python, but in general it's the way to go.

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[Nancy]

I appreciate the clarification on super() - Thanks!