Summary of Python practical skills

The following are some practical Python tips and tools that I have collected in recent years. I hope they will be helpful to you.

Exchange variables

x = 6

y = 5

x, y = y, x

print x

>>> 5

print y

>>> 6

if statement inline

print "Hello" if True else "World"

>>Hello

Connection

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

nfc = ["Packers", "49ers"]

afc = ["Ravens", "Patriots"]

print nfc + afc

>>> ['Packers', '49ers', 'Ravens', 'Patriots']

print str(1) + " world"

>>> 1 world

print `1` + " world"

>>> 1 world

print 1, "world"

> >> 1 world

print nfc, 1

>>> ['Packers', '49ers'] 1

Number skills

#Round down after division

print 5.0//2

>>> 2

# 2 to the 5th power

print 2**5

>> 32

Pay attention to the division of floating point numbers

print .3/.1

>>> 2.9999999999999996

print .3//. 1

>>> 2.0

Numerical comparison

This is such a great simple method that I have seen in many languages

x = 2

if 3 > x > 1:

print x

>>> 2

if 1 0:

print x

>>> 2

Iterate two lists at the same time

nfc = ["Packers", "49ers"]

afc = ["Ravens", "Patriots"]

for teama, teamb in zip(nfc, afc):

  print teama + " vs. " + teamb

>>> Packers vs. Ravens

>>> 49ers vs. Patriots

belt List iteration of index

teams = ["Packers", "49ers", "Ravens", "Patriots"]

for index, team in enumerate(teams):

print index, team

>>> 0 Packers

>>> 1 49ers

>>> 2 Ravens

>>> 3 Patriots

List comprehension

Given a list, we can select the even list method:

numbers = [1,2 ,3,4,5,6]

even = []

for number in numbers:

if number%2 == 0:

even.append(number)

converts to the following:

numbers = [1,2,3,4,5,6]

even = [number for number in numbers if number%2 == 0]

Isn’t it awesome, haha.

Dictionary comprehension

Similar to list comprehensions, dictionaries can do the same job:

teams = ["Packers", "49ers", "Ravens", "Patriots"]

print {key: value for value, key in enumerate(teams)}

>>> {'49ers': 1, 'Ravens': 2, 'Patriots': 3, 'Packers': 0}

Value of initialization list

items = [0]* 3

print items

>>> [0,0,0]

Convert list to string

teams = ["Packers", "49ers", "Ravens", "Patriots"]

print ", ".join(teams)

>>> 'Packers, 49ers, Ravens, Patriots'

Get elements from a dictionary

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

data = {'user': 1, 'name': 'Max', 'three': 4}

try:

is_admin = data['admin']

except KeyError:

is_admin = False

Replace like this:

data = {'user': 1, 'name': 'Max', 'three': 4}

is_admin = data.get('admin', False)

Get the child of the list Sets

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

x = [1,2,3,4,5,6]

#First 3

print x[:3]

>>> [1,2,3]

#Middle 4

print x[1:5]

>>> [2,3,4,5]

#The last 3

print x[-3:]

>>> [4,5,6]

#Odd items

print x[::2]

>>> [1,3,5]

#Even items

print x[1::2]

>>> [2,4, 6]

60 characters to solve FizzBuzz

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

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

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

1

for x in range(101):print"fizz"[x%3*4::]+"buzz"[x%5* 4::]or If you participated in this year's Facebook HackerCup, you can even find its practicality.

from collections import Counter

print Counter("hello")

>>> Counter({'l': 2, 'h': 1, 'e': 1, 'o': 1})

Iterative 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

>>> ('Packers', '49ers')

>> ('Packers', 'Ravens')

>>> ('Packers', 'Patriots')

>>> ('49ers', 'Ravens')

>>> ('49ers' , 'Patriots')

>>> ('Ravens', 'Patriots')

False == True

This is a very interesting thing compared to practical technology. In python, True and False are global variable, therefore:

False = True

if False:

print "Hello"

else:

print "World"

>>> Hello