Access static variable of outer class

Question

In a python project I've been using static members of nested classes to store static configuration (e.g. table names for external data-stores and validation functions for data structures)

class a(object):
    foo = 1
    bar = 2

    class b(object):
        spam = "spam"

    class c(object):
        eggs = "eggs"

This allows me to quickly and easily get a config lookup, which my IDE (pycharm) can type/existence check and suggest auto-completions as I write code.

>>> a.b.spam
'spam'
>>> a.c.eggs
'eggs'

Suppose now, I want to add another nested class which refers to static members of a:

class a(object):
    foo = 1
    bar = 2

    class b(object):
        spam = "spam"

    class c(object):
        eggs = "eggs"

    class d(object):
        spams = "spam" * a.bar
        spam_and_eggs = a.b.spam + a.c.eggs

In a python console, this works as I'd like:

>>> a.d.spams
'spamspam'
>>> a.d.spam_and_eggs
'spameggs'

But putting the above into a .py file and running it as a module, I get name-errors:

Traceback (most recent call last):
  File "/usr/lib64/python3.7/runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "/usr/lib64/python3.7/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/home/me/example/test.py", line 1, in <module>
    class a(object):
  File "/home/me/example/test.py", line 11, in a
    class d(object):
  File "/home/me/example/test.py", line 12, in d
    spams = "spam" * a.bar
NameError: name 'a' is not defined

Is there a combination of imports or a way I could solve this name-error? Alternatively is there a more pythonic way to implement this style of configuration which is free from this issue?

This seems an overly complicated approach. Wouldn't a named tuple work? — StefOverflow
– StefOverflow, Commented Jan 27, 2020 at 10:42
@StefOverflow I think that named tuples would make sense if I were using several different instantiations of the configuration and changing the schema infrequently. (To add a new branch, I'd need to define a new named-tuple-type and then make sure the instantiation stays in sync) In my use case, I only ever need one instance of the config, & I expect to change the code in the config relatively frequently. In my case, I think that the static-class nesting works neatly, because to add a new entry, I just add a new nested class to the tree, and hte shape and data of the tree stay together. — Xandros
– Xandros, Commented Jan 27, 2020 at 11:40

StefOverflow · Accepted Answer · 2020-01-27 10:47:24Z

1

Would defining d after a and monkey-patching a be an option for you?

class a(object):
    foo = 1
    bar = 2

    class b(object):
        spam = "spam"

    class c(object):
        eggs = "eggs"


class d(object):
    spams = "spam" * a.bar
    spam_and_eggs = a.b.spam + a.c.eggs


a.d = d

print(a.d.spams)
# spamspam

I am not sure PyCharm will inspect this correctly, but at least the code would work.

answered Jan 27, 2020 at 10:47

StefOverflow

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