What are the three ways to import the Python module?
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1. Import
> 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']
The most common way is to write the name of the module to be imported directly after the import.
2. From... Import...
Similar to import, except that it is more specific about the methods or variables to import, such as:
> 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']
However, it can cause namespace pollution, so import is recommended.
3. Import a module with a name string
We might want to import the module like this:
> > import "sys"
SyntaxError: invalid syntax
Python import receives variables instead of strings, so what about assigning "sys" to a variable?
> x = "sys"
> import x
Traceback (most recent call last):
File "", line 1, in
Import x
ImportError: No module named'x'
This doesn't work either, which means importing a module named x instead of the sys module represented by x.
We need to use the exec function:
> x = "sys"
> exec ("import" + x)
Sys.path which gynecology hospital in Zhengzhou is good for http://www.sptdfk.com/
['','C:\\ Python34\\ Lib\\ idlelib','C:\\ Windows\\ system32\\ python34.zip','C:\\ Python34\\ DLLs','C:\\ Python34\\ lib','C:\\ Python34','C:\\ Python34\\ lib\\ site-packages']
The import statement is built into a string and passed to the exec function for execution.
The disadvantage of exec is that it has to be compiled every time it is executed, and running multiple times will affect performance.
A better way is to use the _ _ import__ function.
> 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']
This approach requires a variable to hold the module object for subsequent calls.
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