blocks|key|3985141|text|numpy是最顶层的包名，执行import+numpy不会导入子模块numpy.f2py。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3985142|当您执行import+numpy时，它会创建一个指向numpy的链接，但numpy不会进一步链接到f2py。执行import+numpy.f2py操作时，将建立链接|3985143|在上面的代码中：|3985144|import+numpy+as+np+#+np+is+an+alias+pointing+to+numpy,+but+at+this+point+numpy+is+not+linked+to+numpy.f2py
import+numpy.f2py+as+myf2py+#+this+command+makes+numpy+link+to+numpy.f2py.+myf2py+is+another+alias+pointing+to+numpy.f2py+as+well|code-block|syntax|javascript|3985145|下面是import+numpy.f2py和import+numpy.f2py+as+myf2py之间的区别|3985146|3985147|import+numpy.f2py+numpy+|unordered-list-item|3985148|将numpy放入本地符号表(指向numpy)，numpy链接到numpy.f2py|3985149|both+numpy和numpy.f2py为accessible|BOLD|3985150|3985151|​|3985152|3985153|import+numpy.f2py+as+myf2py+parent+|3985154|将父编号放入本地符号表(指向numpy.f2py)|3985155|Its+不会添加到本地符号表中。因此，您无法访问numpy+directly|3985156|3985157|3985158|entityMap^0|F|C|Y|A|0|4|C|Q|5|10|5|1D|4|1K|H|0|0|0|3|H|L|R|0|0|0|H|0|0|5|5|B|A|0|0|0|0|0|R|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1D|8|@$9|1E|A|1F|B|C]|$9|1G|A|1H|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1I|8|@$9|1J|A|1K|B|C]|$9|1L|A|1M|B|C]|$9|1N|A|1O|B|C]|$9|1P|A|1Q|B|C]|$9|1R|A|1S|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|1T|8|@]|D|@]|E|$]]|$1|J|3|K|5|L|7|1U|8|@]|D|@]|E|$M|N]]|$1|O|3|P|5|6|7|1V|8|@$9|1W|A|1X|B|C]|$9|1Y|A|1Z|B|C]]|D|@]|E|$]]|$1|Q|3|-4|5|6|7|20|8|@]|D|@]|E|$]]|$1|R|3|S|5|T|7|21|8|@$9|22|A|23|B|C]]|D|@]|E|$]]|$1|U|3|V|5|T|7|24|8|@]|D|@]|E|$]]|$1|W|3|X|5|T|7|25|8|@$9|26|A|27|B|Y]|$9|28|A|29|B|Y]]|D|@]|E|$]]|$1|Z|3|-4|5|6|7|2A|8|@]|D|@]|E|$]]|$1|10|3|11|5|6|7|2B|8|@]|D|@]|E|$]]|$1|12|3|-4|5|6|7|2C|8|@]|D|@]|E|$]]|$1|13|3|14|5|T|7|2D|8|@$9|2E|A|2F|B|C]]|D|@]|E|$]]|$1|15|3|16|5|T|7|2G|8|@]|D|@]|E|$]]|$1|17|3|18|5|T|7|2H|8|@]|D|@]|E|$]]|$1|19|3|-4|5|6|7|2I|8|@]|D|@]|E|$]]|$1|1A|3|11|5|6|7|2J|8|@]|D|@]|E|$]]|$1|1B|3|-4|5|6|7|2K|8|@]|D|@]|E|$]]]|1C|$]]

numpy is the top package name, and doing <code>import numpy</code> doesn't import submodule <code>numpy.f2py</code>. 

When you do <code>import numpy</code> it creats a link that points to <code>numpy</code>, but <code>numpy</code> is not further linked to <code>f2py</code>. The link is established when you do <code>import numpy.f2py</code>

In your above code:

<pre><code>import numpy as np # np is an alias pointing to numpy, but at this point numpy is not linked to numpy.f2py
import numpy.f2py as myf2py # this command makes numpy link to numpy.f2py. myf2py is another alias pointing to numpy.f2py as well
</code></pre>

Here is the difference between <code>import numpy.f2py</code> and <code>import numpy.f2py as myf2py</code>:

<ul>
<li><code>import numpy.f2py</code>
<ul>
<li>put numpy into local symbol table(pointing to numpy), and numpy is linked to numpy.f2py</li>
<li>both numpy and numpy.f2py are accessible</li>
</ul></li>
<li><code>import numpy.f2py as myf2py</code>
<ul>
<li>put my2py into local symbol table(pointing to numpy.f2py)</li>
<li>Its parent numpy is not added into local symbol table. Therefore you can not access numpy directly</li>
</ul></li>
</ul>

blocks|key|1875290|text|numpy.f2py实际上是numpy的一个子模块，因此必须从numpy单独导入。正如aha之前所说：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1875291|1875292|当您导入numpy时，它会创建一个指向numpy的链接，但numpy不会进一步链接到f2py。链接是在导入numpy.f2py时建立的|blockquote|1875293|1875294|1875295|当您调用语句import+numpy+as+np时，您将短语"numpy“缩短为"np”，以使代码更易于阅读。它还有助于避免名称空间问题。(tkinter和ttk是一个很好的例子，说明了当你遇到这个问题时会发生什么。UI看起来非常不同。)|1875296|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/users/2583917/aha^0|0|A|E|5|17|3|0|0|0|0|0|0|6|I|0^^$0|@$1|2|3|4|5|6|7|V|8|@$9|W|A|X|B|C]|$9|Y|A|Z|B|C]]|D|@$9|10|A|11|1|12]]|E|$]]|$1|F|3|-4|5|6|7|13|8|@]|D|@]|E|$]]|$1|G|3|H|5|I|7|14|8|@]|D|@]|E|$]]|$1|J|3|-4|5|6|7|15|8|@]|D|@]|E|$]]|$1|K|3|-4|5|6|7|16|8|@]|D|@]|E|$]]|$1|L|3|M|5|6|7|17|8|@$9|18|A|19|B|C]]|D|@]|E|$]]|$1|N|3|-4|5|6|7|1A|8|@]|D|@]|E|$]]]|O|$P|$5|Q|R|S|E|$T|U]]]]

<code>numpy.f2py</code> is actually a submodule of <code>numpy</code>, and therefore has to be imported separately from numpy. As <a href="https://stackoverflow.com/users/2583917/aha">aha</a> said before:

<blockquote>
 When you do import numpy it creats a link that points to numpy, but
 numpy is not further linked to f2py. The link is established when you
 do import numpy.f2py
</blockquote>

when you call the statement <code>import numpy as np</code>, you are shortening the phrase "numpy" to "np" to make your code easier to read. It also helps to avoid namespace issues. (tkinter and ttk are a good example of what can happen when you do have that issue. The UIs look extremely different.)

blocks|key|3985194|text|这是一种语言特性。f2py是模块numpy的子包，必须单独加载。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3985195|此功能允许：|3985196|3985197|您可以只从numpy加载所需的包，从而加快执行速度。|unordered-list-item|3985198|+f2py的开发人员可以将命名空间与另一个子包的开发人员分开。|3985199|3985200|但是请注意，import+numpy.f2py或其变体import+numpy.f2py+as+myf2py仍在加载父模块numpy。|3985201|说过，当你跑步的时候|3985202|import+numpy+as+np
np.f2py|code-block|syntax|javascript|3985203|您会收到一个AttributeError，因为f2py不是numpy的属性，因为包numpy的__init__()在其作用域中没有声明有关子包f2py的任何内容。|3985204|entityMap^0|9|4|G|5|0|0|0|5|5|0|1|4|0|0|6|H|R|R|1P|5|0|0|0|6|E|N|4|T|5|15|5|1B|A|1Z|4|0^^$0|@$1|2|3|4|5|6|7|11|8|@$9|12|A|13|B|C]|$9|14|A|15|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|16|8|@]|D|@]|E|$]]|$1|H|3|-4|5|6|7|17|8|@]|D|@]|E|$]]|$1|I|3|J|5|K|7|18|8|@$9|19|A|1A|B|C]]|D|@]|E|$]]|$1|L|3|M|5|K|7|1B|8|@$9|1C|A|1D|B|C]]|D|@]|E|$]]|$1|N|3|-4|5|6|7|1E|8|@]|D|@]|E|$]]|$1|O|3|P|5|6|7|1F|8|@$9|1G|A|1H|B|C]|$9|1I|A|1J|B|C]|$9|1K|A|1L|B|C]]|D|@]|E|$]]|$1|Q|3|R|5|6|7|1M|8|@]|D|@]|E|$]]|$1|S|3|T|5|U|7|1N|8|@]|D|@]|E|$V|W]]|$1|X|3|Y|5|6|7|1O|8|@$9|1P|A|1Q|B|C]|$9|1R|A|1S|B|C]|$9|1T|A|1U|B|C]|$9|1V|A|1W|B|C]|$9|1X|A|1Y|B|C]|$9|1Z|A|20|B|C]]|D|@]|E|$]]|$1|Z|3|-4|5|6|7|21|8|@]|D|@]|E|$]]]|10|$]]

This is a language feature. <code>f2py</code> is a subpackage of the module <code>numpy</code> and must be loaded separately.

This feature allows:

<ul>
<li>you to load from <code>numpy</code> only the packages you need, speeding up execution.</li>
<li>the developers of <code>f2py</code> to have namespace separation from the developers of another subpackage.</li>
</ul>

Notice however that <code>import numpy.f2py</code> or its variant <code>import numpy.f2py as myf2py</code> are still loading the parent module <code>numpy</code>.

Said that, when you run

<pre><code>import numpy as np
np.f2py
</code></pre>

You receive an <code>AttributeError</code> because <code>f2py</code> is not an attribute of <code>numpy</code>, because the <code>__init__()</code> of the package <code>numpy</code> did not declare in its scope anything about the subpackage <code>f2py</code>.

blocks|key|1555483|text|import+as语法是在PEP+221中引入的，在那里有很好的文档记录。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1555484|当您通过导入模块时|1555485|import+numpy|code-block|syntax|javascript|1555486|numpy包被绑定到本地变量numpy。import+as语法只允许您将导入绑定到您选择的本地变量名(通常是为了避免名称冲突，缩短详细的模块名称，或者使用兼容的API标准化对模块的访问)。|1555487|因此，|1555488|import+numpy+as+np|1555489|等同于，|1555490|import+numpy
np+=+numpy
del+numpy|1555491|在试图理解这种机制时，值得记住的是，import+numpy实际上就是import+numpy+as+numpy。|1555492|在导入子模块时，您必须引用完整的父模块名称，因为导入机制发生在比局部变量作用域更高的级别。即|1555493|import+numpy+as+np
import+numpy.f2py+++#+OK
import+np.f2py++++++#+ImportError|1555494|我也反对你的断言，即“在可能的情况下，应该将numpy导入为np”。这样做是有历史原因的，主要是因为人们很快就厌倦了在每个操作前加上numpy。对我来说，它从未阻止过名称冲突(程序员的懒惰实际上表明与np发生冲突的可能性更高)|1555495|最后，为了结束我的演讲，这里有两个您应该知道的import+as机制的有趣用法：|1555496|1.长子导入|1555497|import+scipy.ndimage.interpolation+as+warp
warp.affine_transform(I,+...)|1555498|2.兼容的APIs|1555499|try:
++++import+pyfftw.interfaces.numpy_fft+as+fft
except:
++++import+numpy.fft+as+fft
#+call+fft.ifft(If)+with+fftw+or+the+numpy+fallback+under+a+common+name|1555500|entityMap|0|LINK|mutability|MUTABLE|url|http://legacy.python.org/dev/peps/pep-0221/^0|0|9|D|7|0|0|0|0|E|5|K|9|0|0|0|0|0|I|C|Z|L|0|0|0|1U|5|2S|2|0|N|9|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1M|8|@$9|1N|A|1O|B|C]]|D|@$9|1P|A|1Q|1|1R]]|E|$]]|$1|F|3|G|5|6|7|1S|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|1T|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|1U|8|@$9|1V|A|1W|B|C]|$9|1X|A|1Y|B|C]]|D|@]|E|$]]|$1|O|3|P|5|6|7|1Z|8|@]|D|@]|E|$]]|$1|Q|3|R|5|J|7|20|8|@]|D|@]|E|$K|L]]|$1|S|3|T|5|6|7|21|8|@]|D|@]|E|$]]|$1|U|3|V|5|J|7|22|8|@]|D|@]|E|$K|L]]|$1|W|3|X|5|6|7|23|8|@$9|24|A|25|B|C]|$9|26|A|27|B|C]]|D|@]|E|$]]|$1|Y|3|Z|5|6|7|28|8|@]|D|@]|E|$]]|$1|10|3|11|5|J|7|29|8|@]|D|@]|E|$K|L]]|$1|12|3|13|5|6|7|2A|8|@$9|2B|A|2C|B|C]|$9|2D|A|2E|B|C]]|D|@]|E|$]]|$1|14|3|15|5|6|7|2F|8|@$9|2G|A|2H|B|C]]|D|@]|E|$]]|$1|16|3|17|5|6|7|2I|8|@]|D|@]|E|$]]|$1|18|3|19|5|J|7|2J|8|@]|D|@]|E|$K|L]]|$1|1A|3|1B|5|6|7|2K|8|@]|D|@]|E|$]]|$1|1C|3|1D|5|J|7|2L|8|@]|D|@]|E|$K|L]]|$1|1E|3|-4|5|6|7|2M|8|@]|D|@]|E|$]]]|1F|$1G|$5|1H|1I|1J|E|$1K|1L]]]]

The <code>import as</code> syntax was introduced in <a href="http://legacy.python.org/dev/peps/pep-0221/">PEP 221</a> and is well documented there.

When you import a module via

<pre><code>import numpy
</code></pre>

the numpy package is bound to the local variable <code>numpy</code>. The <code>import as</code> syntax simply allows you to bind the import to the local variable name of your choice (usually to avoid name collisions, shorten verbose module names, or standardize access to modules with compatible APIs).

Thus,

<pre><code>import numpy as np
</code></pre>

is equivalent to,

<pre><code>import numpy
np = numpy
del numpy
</code></pre>

When trying to understand this mechanism, it's worth remembering that <code>import numpy</code> actually means <code>import numpy as numpy</code>.

When importing a submodule, you must refer to the full parent module name, since the importing mechanics happen at a higher level than the local variable scope. i.e.

<pre><code>import numpy as np
import numpy.f2py # OK
import np.f2py # ImportError
</code></pre>

I also take issue with your assertion that "where possible one should [import numpy as np]". This is done for historical reasons, mostly because people get tired very quickly of prefixing every operation with <code>numpy</code>. It has never prevented a name collision for me (laziness of programmers actually suggests there's a higher probability of causing a collision with <code>np</code>)

Finally, to round out my exposé, here are 2 interesting uses of the <code>import as</code> mechanism that you should be aware of:

<h3>1. long subimports</h3>

<pre><code>import scipy.ndimage.interpolation as warp
warp.affine_transform(I, ...)
</code></pre>

<h3>2. compatible APIs</h3>

<pre><code>try:
 import pyfftw.interfaces.numpy_fft as fft
except:
 import numpy.fft as fft
# call fft.ifft(If) with fftw or the numpy fallback under a common name
</code></pre>

blocks|key|1555515|text|这是一个相当古老的帖子，但这里是我对其他人提供的解释的2分钱。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1555516|numpy+(参考git存储库)包有各种子包，f2py是其中之一，其他作为核心，ma等等|1555517|如果您在包中引用numpy+init.py，它具有如下导入-|offset|length|style|BOLD|1555518|from+.+import+core+etc+|code-block|syntax|javascript|1555519|但是它没有任何f2py子包的导入。这就是为什么像这样的语句|1555520|import+numpy+as+np
np.f2py|1555521|不会工作，但是|1555522|import+numpy+as+np
np.core|1555523|都会起作用的。|1555524|entityMap^0|0|0|4|E|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|11|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|12|8|@$F|13|G|14|H|I]]|9|@]|A|$]]|$1|J|3|K|5|L|7|15|8|@]|9|@]|A|$M|N]]|$1|O|3|P|5|6|7|16|8|@]|9|@]|A|$]]|$1|Q|3|R|5|L|7|17|8|@]|9|@]|A|$M|N]]|$1|S|3|T|5|6|7|18|8|@]|9|@]|A|$]]|$1|U|3|V|5|L|7|19|8|@]|9|@]|A|$M|N]]|$1|W|3|X|5|6|7|1A|8|@]|9|@]|A|$]]|$1|Y|3|-4|5|6|7|1B|8|@]|9|@]|A|$]]]|Z|$]]

Well quite an old post but here are my 2 cents over the explanation provided by others.

numpy (refer git repository) package have various subpackages, f2py is one of them other are as core, ma etc

If you refer the init.py in numpy package it has imports like - 

<pre><code>from . import core etc 
</code></pre>

but it's not having any import for f2py subpackage.
That's the reason that a statement like 

<pre><code>import numpy as np
np.f2py
</code></pre>

won't work but 

<pre><code>import numpy as np
np.core
</code></pre>

will work.

I understand that when possible one should use 

<pre><code>import numpy as np
</code></pre>

This helps keep away any conflict due to namespaces. But I have noticed that while the command below works

<pre><code>import numpy.f2py as myf2py
</code></pre>

the following does not

<pre><code>import numpy as np
np.f2py #throws no module named f2py
</code></pre>

Can someone please explain this?

Difference between import numpy and import numpy as np

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我理解在可能的情况下应该使用import numpy as np这有助于避免由于名称空间而导致的任何冲突。但我注意到，虽然下面的命令可以正常工作import numpy.f2py as myf2py以下内容不支持import numpy as npnp.f2py #throws no module named f2py...

问导入numpy与将numpy导入为np的区别
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