from … import OR import … as for modules

Question

Should I use

from foo import bar

OR

import foo.bar as bar

when importing a module and an

Answer 1

Both are technically different:

• import torch.nn as nn will only import a module/package torch.nn, wheres
• from torch import nn can and will prefer to import an attribute .nn from the torch module/package. Importing a module/package torch.nn is a fall.back.

In practice, it is bad style to have the same fully qualified name refer to two separate things. As such, torch.nn should only refer to a module/package. In this common case, both import statements are functionally equivalent: The same object is imported and bound to the same name.

Which one to choose comes down to preference if the target always is a module. There are practical differences when refactoring:

• import torch.nn as nn guarantees .nn is a module/package. It protects against accidentally shadowing with an attribute.
• from torch import nn does not care what .nn is. It allows to transparently change the implementation.

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7.11. The import statement

The basic import statement (no from clause) is executed in two steps:

1. find a module, loading and initializing it if necessary
2. define a name or names in the local namespace for the scope where the import statement occurs.

[...]

The from form uses a slightly more complex process:

1. find the module specified in the from clause, loading and initializing it if necessary;

2. for each of the identifiers specified in the import clauses:

   1. check if the imported module has an attribute by that name
   2. if not, attempt to import a submodule with that name and then check the imported module again for that attribute