# Importing Submodules

When importing parts of the zef module as an external user, extension submodule,
or core development, there are rules about imports which should be followed. The
below is a list of import styles possible, in order of external to core development.

An exception to all of the rules below is that any imports inside of a
function
can access any other part of the library, so long as that function is
not called as part of the initialization of the zef module. Stick to relative
imports where possible.

## As a user of the module​

Generally, a user will call:

from zef import *  from zef.ops import *  

Using extension zef modules is done via

from zef.gql import *  

If they need anything more specific, they can call, e.g.

from zef.core.fx import _Effect_Class  

## As an extension module writer​

This is, e.g., development of the gql extension submodule.

Always use relative imports. Most features are available in a similar manner to
an external user.

from ..core import *  from ..ops import *  

## When developing the ops submodule​

Always use relative imports. The core operators should be imported from the
core.op_names module.

from ..core import *  from ..core.op_names import *  

If usage of another ZefOp that is outside of the core ZefOps is required, then
access this relatively:

from .privileges import grant  

## When implementing a core ZefOp​

This means touching anything inside of zefDB/core/op_implementations/*. This is
a special case, where we can still import everything from core:

from .. import *  from ..op_names import *  

All core things, like GraphDelta, GraphSlice, FX, etc... will be
available. In addition, all core zefops (i.e. those that appear in op_names)
will be available. However, ops that are later defined in zefDB/ops will not
be available. I recommend that core zefops should only depend on other core
zefops.

If something more specific is required, use a relative import:

from ..fx.fx_types import _Effect_Class  

## When developing a submodule of core​

For example, this could be graph_delta.py or anything inside of fx.

from ._core import *  from .op_names import *  

A large part is exposed through _core, which includes ZefRef, ET,
Transaction, etc... and the core ZefOps will be exposed through op_names.
However, you will not have immediate access to other things that would normally
be found through a from zef.core import * call.

If anything else is required, import that specifically, e.g. inside of
graph_delta.py:

from .zef_functions import func  

Note that you must not break the dependency ordering, which is currently (look
at core/__init__.py for the latest):

• internals
• error
• op_structs
• op_names
• zef_functions
• abstract_raes
• graph_delta
• graph_slice
• fx
• serialization

Hence, graph_delta.py is not allowed to import from fx at the top-level scope.

## When developing core itself​

This is really only addressing the submodules:

• core/_core
• core/internals/...
• core/patching
• core/overrides

In these submodules, everything should only access the C bindings or each other.