Python Note 7: Elegant python

7. How to make Python code morePythonic:

1. Variable Exchange:

A, B = B, a

2 . Set traversal with index position:

colors = ['red'Green'blue ' ' Yellow ' ] for in Enumerate (colors):print'--->  ', color

3. String Connection:

names = ['Raymond','Rachel','Matthew','Roger','Betty','Melissa','Judith','Charlie']Print ', '. Join (names)

Note: When using the + operation, a new string object is generated in memory each time, and the Join method produces only one string object.
4. Open/Close files:

With open ('data.txt'= F.read ()

Note: With the WITH statement, the file object is closed automatically after the file operation is performed.
5. Rational use of the list

 fromCollectionsImportDequenames= Deque (['Raymond','Rachel','Matthew','Roger','Betty','Melissa','Judith','Charlie']) names.popleft ()#Delete the leftmost elementNames.appendleft ('Mark')#add a new element on the far left

Note: The list of lists is a data structure that is more efficient than the update operation, and is inefficient when deleting and inserting new elements, and queue deque is a two-way queue data structure that removes elements and inserts elements quickly
6. Sequence Unpacking:

' Vttalk ' ' female ' ' [email protected] '  = P

7 . Traverse the dictionary key and value

 for inch D.iteritems (): Note: Iteritems returns an Iterator object, only the items method in Python3, equivalent to Iteritems Print ' ---> ', V

8. Chain comparison operation: If < Age < 60:

Guess:>>> false = = False = = True (The answer is: false)

9,if/else three mesh operation:

' male ' if ' male ' Else ' female '

10, truth value judgment:

if  If attr = = True:if not if#  Determines if the list is empty

11.For/else Statement
For else is a specific syntax format in Python, and the code in else executes after the for loop has traversed all elements
12. Get dictionary elements

D = {'name''foo'}d.get ("name " " Unknow " # if D has key=name, it gets its value, otherwise key=unknow

13. Preset Dictionary default value
(Scenario: When you are grouping by key, you have to check that the key is already in the dictionary every time.) ）

Groups = {} for in # mode one, commonly used

14. Dictionary derivation style

numbers = [1, 2, 3forif number > 1}print# {2:4, 3:6}

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Python Note 7: Elegant python