## 6.4.2 Intra-package References

The submodules often need to refer to each other. For example, the `surround` module might use the `echo` module. In fact, such references are so common that the `import` statement first looks in the containing package before looking in the standard module search path. Thus, the surround module can simply use `import echo` or `from echo import echofilter`. If the imported module is not found in the current package (the package of which the current module is a submodule), the `import` statement looks for a top-level module with the given name.

When packages are structured into subpackages (as with the `Sound` package in the example), there's no shortcut to refer to submodules of sibling packages - the full name of the subpackage must be used. For example, if the module `Sound.Filters.vocoder` needs to use the `echo` module in the `Sound.Effects` package, it can use `from Sound.Effects import echo`.