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Summarize some Python programming skills

伊谢尔伦

Release： 2017-06-28 13:17:14

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This article mainly introduces some programming skills for Python beginners. They are all based on some basic programming habit suggestions. Friends in need can refer to

Exchange Variables

x = 6
y = 5
 
x, y = y, x
 
print x
>>> 5
print y
>>> 6

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if statement in line

print "Hello" if True else "World"
>>> Hello

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Connection

The last way below is very cool when binding two objects of different types.

nfc = ["Packers", "49ers"]
afc = ["Ravens", "Patriots"]
print nfc + afc
>>> [&#39;Packers&#39;, &#39;49ers&#39;, &#39;Ravens&#39;, &#39;Patriots&#39;]
 
print str(1) + " world"
>>> 1 world
 
print `1` + " world"
>>> 1 world
 
print 1, "world"
>>> 1 world
print nfc, 1
>>> [&#39;Packers&#39;, &#39;49ers&#39;] 1

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Number skills

#除后向下取整
print 5.0//2
>>> 2
# 2的5次方
print 2**5
>> 32

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Pay attention to the division of floating point numbers

print .3/.1
>>> 2.9999999999999996
print .3//.1
>>> 2.0

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Numeric values Compare

This is one of the few multilingual I have seen such a great simple method

x = 2
if 3 > x > 1:
 print x
>>> 2
if 1 < x > 0:
 print x
>>> 2

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Iterate over two lists simultaneously

nfc = ["Packers", "49ers"]
afc = ["Ravens", "Patriots"]
for teama, teamb in zip(nfc, afc):
  print teama + " vs. " + teamb
>>> Packers vs. Ravens
>>> 49ers vs. Patriots

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Indexed list iteration

teams = ["Packers", "49ers", "Ravens", "Patriots"]
for index, team in enumerate(teams):
 print index, team
>>> 0 Packers
>>> 1 49ers
>>> 2 Ravens
>>> 3 Patriots

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List comprehension

Given a list, we can brush out the even-numbered list method:

numbers = [1,2,3,4,5,6]
even = []
for number in numbers:
 if number%2 == 0:
  even.append(number)

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transforms into the following:

numbers = [1,2,3,4,5,6]
even = [number for number in numbers if number%2 == 0]

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Isn’t it awesome, haha.

Dictionary comprehension

Similar to list comprehension, a dictionary can do the same job:

teams = ["Packers", "49ers", "Ravens", "Patriots"]
print {key: value for value, key in enumerate(teams)}
>>> {&#39;49ers&#39;: 1, &#39;Ravens&#39;: 2, &#39;Patriots&#39;: 3, &#39;Packers&#39;: 0}

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Initialize the value of the list

items = [0]*3
print items
>>> [0,0,0]

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Convert list to string

teams = ["Packers", "49ers", "Ravens", "Patriots"]
print ", ".join(teams)
>>> &#39;Packers, 49ers, Ravens, Patriots&#39;

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Get elements from dictionary

I admit that the try/except code is not elegant, but here is a simple method, try to find the key in the dictionary, if the corresponding alue is not found, the second parameter will be used to set its variable value.

data = {&#39;user&#39;: 1, &#39;name&#39;: &#39;Max&#39;, &#39;three&#39;: 4}
try:
 is_admin = data[&#39;admin&#39;]
except KeyError:
 is_admin = False
1

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Replace with this:

data = {&#39;user&#39;: 1, &#39;name&#39;: &#39;Max&#39;, &#39;three&#39;: 4}
is_admin = data.get(&#39;admin&#39;, False)

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Get a subset of the list

Sometimes, you only want a subset of the list elements, here are some ways to get a subset of a list.

x = [1,2,3,4,5,6]
#前3个
print x[:3]
>>> [1,2,3]
#中间4个
print x[1:5]
>>> [2,3,4,5]
#最后3个
print x[-3:]
>>> [4,5,6]
#奇数项
print x[::2]
>>> [1,3,5]
#偶数项
print x[1::2]
>>> [2,4,6]

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60 characters to solve FizzBuzz

Some time ago Jeff Atwood promoted a simple programming exercise called FizzBuzz. The question is quoted as follows ：

Write a program that prints the numbers 1 to 100. Multiples of 3 print "Fizz" to replace this number. Multiples of 5 print "Buzz". For numbers that are both multiples of 3 and 5, print "FizzBuzz".

Here is a short, interesting way to solve this problem:

for x in range(101):print"fizz"[x%3*4::]+"buzz"[x%5*4::]or x

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Collection

In addition to python’s built-in data In addition to type, the collection module also includes some special use cases. Counter is very practical in some situations. If you participated in this year's Facebook HackerCup, you can even find its practicality.

from collections import Counter
print Counter("hello")
>>> Counter({&#39;l&#39;: 2, &#39;h&#39;: 1, &#39;e&#39;: 1, &#39;o&#39;: 1})

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Iteration tools

Like the collections library, there is also a library called itertools, which can really solve certain problems efficiently. One use case is to find all combinations, which tells you all the possible combinations of elements in a group

from itertools import combinations
teams = ["Packers", "49ers", "Ravens", "Patriots"]
for game in combinations(teams, 2):
 print game
>>> (&#39;Packers&#39;, &#39;49ers&#39;)
>>> (&#39;Packers&#39;, &#39;Ravens&#39;)
>>> (&#39;Packers&#39;, &#39;Patriots&#39;)
>>> (&#39;49ers&#39;, &#39;Ravens&#39;)
>>> (&#39;49ers&#39;, &#39;Patriots&#39;)
>>> (&#39;Ravens&#39;, &#39;Patriots&#39;)

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False == True

than This is a very interesting thing from a practical technical point of view. In python, True and False are global variables, so:

False = True
if False:
 print "Hello"
else:
 print "World"
>>> Hello

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