Python3 base Assert assertion ensures correct running conditions for the program

Town Field Poem:
Cheng listens to the Tathagata language, the world name and benefit of Dayton. Be willing to do the Tibetan apostles, the broad show is by Sanfu mention.
I would like to do what I learned, to achieve a conscience blog. May all the Yimeimei, reproduce the wisdom of the body.
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Code

Data=int (Input (' Enter an integer: ')) asserts the data >= 0    #当data小于0时, triggering this exception if the   <= data <=:    print (str (data) + ' between 90 and 100 ') elif <= data <=:    print (str (data) + ' between 80 and 90 ') Else:    print (str (data) + ' less than 80 ')

Result x 2:

============= restart:c:/users/administrator/desktop/mytest.py ============= Enter an integer: -1traceback (most recent call Last):  File ' c:/users/administrator/desktop/mytest.py ', line 3, <module>    assert data >= 0    

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The essence of the blog, in the technical part, more in the town yard a poem. Python version 3.5, System Windows7.
Python is a good language and deserves to be studied hard. I am following the small Turtle Video tutorial to learn, recommended.
I am a novice, so if the content of the blog can be improved, or even the wrong place, please leave a comment, I will try to correct, strive to achieve a conscience blog.
Note: This article is only as a scientific research study, if I inadvertently violated your rights and interests, please be sure to timely inform, I will make corrections.

Python3 base Assert assertion ensures correct running conditions for the program