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Teach you three Python Programming Tips

2022-02-02 03:58:25 Late industry

Share today 3 individual Python Programming tips , Let's see if you've ever used ?

1、 How to sort according to the size of dictionary values

We know , The essence of a dictionary is a hash table , It can't be sorted by itself , but Python 3.6 after , Dictionaries can be traversed in the order of insertion , This is the ordered dictionary , The principle is , You can read Why? Python3.6 After that, the dictionary is in order .

Knowing that , It's easy to do. , First sort the list with the key values of the dictionary , Then re insert the new dictionary , In this way, the new dictionary can traverse the output according to the size of the value . The code is as follows :

>>> xs = {'a': 4, 'b': 3, 'c': 2, 'd': 1}
>>> for k,v in xs.items():# Ergodic dictionary 
...     print(k,v)
...
a 4
b 3
c 2
d 1
>>> new_order = sorted(xs.items(), key=lambda x: x[1]) # Sort the list of key values of the dictionary 

>>> new_xs = { k : v for k,v in new_order} # Insert a new dictionary into the ordered list 
>>> new_xs
{'d': 1, 'c': 2, 'b': 3, 'a': 4}
>>> for k,v in new_xs.items(): ## The output of the new dictionary is ordered 
...     print(k,v)
...
d 1
c 2
b 3
a 4
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Sort the list , You can also use the following methods :

>>> import operator
>>> sorted(xs.items(), key=operator.itemgetter(1))
[('d', 1), ('c', 2), ('b', 3), ('a', 4)]
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2、 Elegant one-time judgment of multiple conditions

If there are three conditions , As long as one is true, you can pass , Maybe you'll write :

x, y, z = 0, 1, 0

if x == 1 or y == 1 or z == 1:
    print('passed')
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actually , The following three methods are more Pythonic

if 1 in (x, y, z):
    print('passed')

if x or y or z:
    print('passed')

if any((x, y, z)):
    print('passed')
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The last one uses Python Built in method  any(),any Accept an iteratable object as a parameter , Such as lists or tuples , As long as one of them is true , be  any()  Method returns true , Usage examples are as follows :

>>> any(['a',(2,4),3,True]) 
True
>>> any(['a',(2,4),3,False])
True
>>> any(['a',(),3,False])   
True
>>> any(['',(),0,False]) 
False
>>> any(('a',(),3,False))
True
>>> any(('',(),0,False)) 
False
##  Note that an empty iteratable object returns  False
>>> any(())
False
>>> any([])
False
>>> any('')
False
>>> any({})
False
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And  any()  Corresponding , That's the way.  all(), Only all are true , Only true , Note that empty iteratable objects always return true .

>>> all(['a',(2,4),1,True]) //list All for " really "
True
>>> all(['a',(),1,True])   //list Empty in element tuple
False
>>> all(['a',(2,4),0,True])
False
>>> all(['a',(2,4),3,False])
False
  
##  Note that an empty iteratable object returns  True
>>>all([])
True 
>>> all(())
True
>>> all({})
True
>>> all('')
True
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View help documents , You can enter... In the interpreter help:

>>> help(all)
Help on built-in function all in module __builtin__:

all(...)
    all(iterable) -> bool

    Return True if bool(x) is True for all values x in the iterable.
    If the iterable is empty, return True.
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3、 How to merge two dictionaries gracefully

Operators can unpack dictionaries , This is very useful when merging dictionaries , such as :

>>> x = {'a': 1, 'b': 2}
>>> y = {'b': 3, 'c': 4}

>>> z = {**x, **y}

>>> z
{'c': 4, 'a': 1, 'b': 3}
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If in Python2.x in , It needs to be done :

>>> z = dict(x, **y)
>>> z
{'a': 1, 'c': 4, 'b': 3}
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Okay , My sharing is over . If other partners have better tips . Welcome to discuss in the comments ! 

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