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Python

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5.2. Importing Modules Using from module import

5.2. Importing Modules Using from module import

Python has two ways of importing modules. Both are useful, and you should know when to use each. One way, import module, you've already seen in Section 2.4, “Everything Is an Object”. The other way accomplishes the same thing, but it has subtle and important differences.

Here is the basic from module import syntax:


from UserDict import UserDict

This is similar to the import module syntax that you know and love, but with an important difference: the attributes and methods of the imported module types are imported directly into the local namespace, so they are available directly, without qualification by module name. You can import individual items or use from module import * to import everything.

Note
from module import * in Python is like use module in Perl; import module in Python is like require module in Perl.
Note
from module import * in Python is like import module.* in Java; import module in Python is like import module in Java.

Example 5.2. import module vs. from module import

>>> import types
>>> types.FunctionType             1
<type 'function'>
>>> FunctionType                   2
Traceback (innermost last):
  File "<interactive input>", line 1, in ?
NameError: There is no variable named 'FunctionType'
>>> from types import FunctionType 3
>>> FunctionType                   4
<type 'function'>
1 The types module contains no methods; it just has attributes for each Python object type. Note that the attribute, FunctionType, must be qualified by the module name, types.
2 FunctionType by itself has not been defined in this namespace; it exists only in the context of types.
3 This syntax imports the attribute FunctionType from the types module directly into the local namespace.
4 Now FunctionType can be accessed directly, without reference to types.

When should you use from module import?

  • If you will be accessing attributes and methods often and don't want to type the module name over and over, use from module import.
  • If you want to selectively import some attributes and methods but not others, use from module import.
  • If the module contains attributes or functions with the same name as ones in your module, you must use import module to avoid name conflicts.

Other than that, it's just a matter of style, and you will see Python code written both ways.

Caution
Use from module import * sparingly, because it makes it difficult to determine where a particular function or attribute came from, and that makes debugging and refactoring more difficult.

Further Reading on Module Importing Techniques

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