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copied!<p>The "advantage" of <code>from xyz import *</code> as opposed to other forms of import is that it imports <em>everything</em> (well, almost... [see (a) below] everything) from the designated module under the current module. This allows using the various objects (variables, classes, methods...) from the imported module <strong>without prefixing them with the module's name</strong>. For example</p> <pre><code>>>> from math import * >>>pi 3.141592653589793 >>>sin(pi/2) >>>1.0 </code></pre> <p><strong>This practice (of importing * into the current namespace) is however discouraged</strong> because it</p> <ul> <li>provides the opportunity for namespace collisions (say if you had a variable name pi prior to the import)</li> <li>may be inefficient, if the number of objects imported is big</li> <li>doesn't explicitly document the origin of the variable/method/class (it is nice to have this "self documentation" of the program for future visit into the code)</li> </ul> <p>Typically we therefore limit this import * practice to ad-hoc tests and the like. As pointed out by @Denilson-Sá-Maia, some libraries such as (e.g. pygame) have a sub-module where all the most commonly used constants and functions are defined and such sub-modules are effectively <em>designed</em> to be imported with <code>import *</code>. Other than with these special sub-modules, it is otherwise preferable to ...:</p> <p><strong>explicitly import a few objects only</strong></p> <pre><code>>>>from math import pi >>>pi >>>3.141592653589793 >>> sin(pi/2) Traceback (most recent call last): File "<stdin>", line 1, in <module> NameError: name 'sin' is not defined </code></pre> <p>or <strong>import the module under its own namespace</strong> (or an alias thereof, in particular if this is a long name, and the program references its objects many times)</p> <pre><code> >>>import math >>>math.pi >>>3.141592653589793 etc.. >>>import math as m #bad example math being so short and standard... >>>m.pi >>>3.141592653589793 etc.. </code></pre> <p>See the <a href="http://docs.python.org/reference/simple_stmts.html#the-import-statement" rel="nofollow noreferrer"><strong>Python documentation on this topic</strong></a></p> <p><strong>(a) Specifically, what gets imported with <code>from xyz import *</code> ?</strong> <br> if xyz module defines an <code>__all__</code> variable, it will import all the names defined in this sequence, otherwise it will import all names, except these which start with an underscore.</p> <p><strong>Note</strong> Many libraries have <strong><em>sub-modules</em></strong>. For example the standard library <code>urllib</code> includes sub-modules like <code>urllib.request</code>, <code>urllib.errors</code>, <code>urllib.response</code> etc. A common point of confusion is that</p> <p><code>from urllib import *</code></p> <p>would import all these sub-modules. <strong>That is NOT the case</strong>: one needs to explicitly imports these separately with, say, <code>from urllib.request import *</code> etc. This incidentally is not specific to <code>import *</code>, plain <code>import</code> will not import sub-modules either (but of course, the <code>*</code> which is often a shorthand for <em>"everything"</em> may mislead people in thinking that all sub-modules and everything else would be imported). </p>

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