Python Note-set

Coding
Unicode, universal code, Unified code, for each language of each character set a unified and unique binary encoding, to meet cross-platform, cross-language text conversion;

Utf-8-8-bit Unicode Transformation Format, variable-length character encoding for Unicode

ASCII code: American Standard Code for information interchange, U.S. Standards for Information interchange codes

gbk-Chinese Character Coded charset
Hash table-is a data structure that is accessed directly based on key value
Objects are created with classes;
How many methods the class has, how many functions the object has

Set set, which does not allow duplicate elements to appear
Fast access to solve repetitive problems
Create: Create by class
S1 = set ()
S1.add (' AAA ')
Print (S1)
S1.add (' CCC ')
Print (S1)
Crawler: Request the page, get the source code, take the element, find the product name, find the price
Crawler has the entrance, find all the links, access to put set inside
Finally, you can determine if there is a URL in set.

CMDB: Acquiring hardware assets
Intersection, Difference set
S1 = set ([11,22,33])
S2 = set ([44,55])

S3 = s1.difference (S2)
S4 = s1.difference_update (S2)
S5 = s1.symmetric_difference (S2)
Print (S3)
Print (S4)
Print (S5)

Collections Series, Collection
The Counter counter, which complements the dictionary type and counts the number of occurrences of a value, inherits the collection class
A = collections. Counter (' Aaaafdsfdsfsdfds ')
Print (a)

Counter ({' A ': 4, ' F ': 4, ' d ': 4, ' s ': 4})

Ordered dictionary Ordereddict

Python Note-set