第499页 | Learning Python | 阅读 ‧ 电子书库

The from * Statement

Finally, the next example uses a special form of from: when we use a *, we get copies of all the names assigned at the top level of the referenced module. Here again, we can then use the copied name printer in our script without going through the module name:

>>> from module1 import *                   # Copy out all variables
>>> printer('Hello world!')
Hello world!

Technically, both import and from statements invoke the same import operation; the from * form simply adds an extra step that copies all the names in the module into the importing scope. It essentially collapses one module’s namespace into another; again, the net effect is less typing for us.

And that’s it—modules really are simple to use. To give you a better understanding of what really happens when you define and use modules, though, let’s move on to look at some of their properties in more detail.

Note

In Python 3.0, the from ...* statement form described here can be used only at the top level of a module file, not within a function. Python 2.6 allows it to be used within a function, but issues a warning. It’s extremely rare to see this statement used inside a function in practice; when present, it makes it impossible for Python to detect variables statically, before the function runs.