Python in several ways summarized import module

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inside the module encapsulates many useful features, sometimes you need to be imported outside the calling module. There are several common ways:

1 . import

<font style="color:rgb(77, 77, 77)"><font face="&quot"><font style="font-size:16px">>>> import sys
>>> sys.path
['', 'C:\\Python34\\Lib\\idlelib', 'C:\\Windows\\system32\\python34.zip', 'C:\\Python34\\DLLs', 'C:\\Python34\\lib', 'C:\\Python34', 'C:\\Python34\\lib\\site-packages']
</font></font></font>

The most common way to import directly to the module name written on the back of the import.

2 .from … import …

And import similar, but more specific method or variable you want to import, such as:

<font style="color:rgb(77, 77, 77)"><font face="&quot"><font style="font-size:16px">>>> from sys import path
>>> path
['', 'C:\\Python34\\Lib\\idlelib', 'C:\\Windows\\system32\\python34.zip', 'C:\\Python34\\DLLs', 'C:\\Python34\\lib', 'C:\\Python34', 'C:\\Python34\\lib\\site-packages']
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But will pollute the namespace, it is recommended to use import.

3. Import module name string

We may want to import this module:

<font style="color:rgb(77, 77, 77)"><font face="&quot"><font style="font-size:16px">>>> import "sys"
SyntaxError: invalid syntax
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python import reception is variable rather than a string, it would be "sys" assignment to a variable it?

<font style="color:rgb(77, 77, 77)"><font face="&quot"><font style="font-size:16px">>>> x="sys"
>>> import x
Traceback (most recent call last):
 File "<pyshell#4>", line 1, in <module>
  import x
ImportError: No module named 'x'
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This does not work, this means that rather than import module x x stands for the name of the sys module.

We need to use the exec function:

<font style="color:rgb(77, 77, 77)"><font face="&quot"><font style="font-size:16px">>>> x="sys"
>>> exec("import "+ x)
>>> sys.path
['', 'C:\\Python34\\Lib\\idlelib', 'C:\\Windows\\system32\\python34.zip', 'C:\\Python34\\DLLs', 'C:\\Python34\\lib', 'C:\\Python34', 'C:\\Python34\\lib\\site-packages']
</font></font></font>

The import statement string and constructed to perform the function passed to exec.

The disadvantage is that each execution to be exec compile, run multiple times can affect performance.

__Import__ better way is to use the function.

<font style="color:rgb(77, 77, 77)"><font face="&quot"><font style="font-size:16px">>>> x="sys"
>>> sys = __import__(x)
>>> sys.path
['', 'C:\\Python34\\Lib\\idlelib', 'C:\\Windows\\system32\\python34.zip', 'C:\\Python34\\DLLs', 'C:\\Python34\\lib', 'C:\\Python34', 'C:\\Python34\\lib\\site-packages']
</font></font></font>

This approach requires a variable to hold the object module, so that subsequent calls.