Calling __init__ for super() with conditional arguments-CodePudding

What would be the pythonic way to achieve the following usecase:

Import a module conditionally
Inherit from that module
Call super.__init__() with parameters based on which module we inherited from

Eg. I am trying to have my app compatible with both cmd and cmd2 module. Since cmd2 supports history, I need to call its init with additional parameters. But it's ok if user doesn't have that module installed

I am handling it this way. Though it works, I don't like the solution myself

try:
    import cmd2 as CMD
except:
    import cmd as CMD

class MyApp(CMD.Cmd):
    def __init__(self):
        if globals()['CMD'].__name__ == "cmd2":
            super().__init__(persistent_history_file="~/myapp_history.dat", allow_cli_args=False)
        else:
            super().__init__()

Note: This question is not specific to cmd/cmd2 module. That is just an example

I am trying to find the best way to achieve this for any such usecase

CodePudding user response：

One approach would be to create an intermediate class based on the imported module in the try-except block, override the __init__ method accordingly in the intermediate class, so that your main class can inherit from it cleanly:

try:
    import cmd2
    class CMD(cmd2.Cmd):
        def __init__(self):
            super().__init__(persistent_history_file="~/myapp_history.dat", allow_cli_args=False)
except:
    import cmd
    class CMD(cmd.Cmd):
        def __init__(self):
            super().__init__()

class MyApp(CMD):
    # define other attributes and methods here
    pass

CodePudding user response：

Usually, you try to import different modules if they have completely same functionality and one had faster speed.

e.g.

try:
    import json5 as json
except ImportError:
    import json
# Pasted from the requests library

In your case, if there's only one difference look at @blhsing's answer. It is a perfect approach without writing too much code.

Otherwise I recommend the following:

use_cmd2 = True
try:
    import cmd2 as CMD
except:
    import cmd as CMD
    use_cmd2 = False

class MyApp(CMD.Cmd):
    def __init__(self):
        if use_cmd2:
            super().__init__(persistent_history_file="~/myapp_history.dat", allow_cli_args=False)
        else:
            super().__init__()

    def foo(self):
        if use_cmd2:
            pass # special
        else:
            pass # ordinary