Some programming skills for beginners of Python

This article mainly introduces some programming skills for beginners of Python, which are based on some basic programming habits. Please refer to
Exchange variables

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

if statement in line

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

Connect

The last way to do this is to bind two different types of objects

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

Digital skills

#Round down after division
print 5.0//2
>>> 2
# The 5 power of 2.
print 2**5
>> 32

Pay attention to division of floating point number

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

Numerical comparison

It's a simple method that I've never seen in many languages

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

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

List derivation

Given a list, we can brush out the even list method

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

Change to the following:

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

Isn't it amazing, ha ha.

Dictionary derivation

Like list derivation, dictionaries can do the same:

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]

List to string

teams = ["Packers", "49ers", "Ravens", "Patriots"]
print ", ".join(teams)
>>> 'Packers, 49ers, Ravens, Patriots'

Get elements from dictionary

I admit that try/except code is not elegant, but here is a simple way to try to find the key in the dictionary. If the corresponding value 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
1

Replace it like this:

data = {'user': 1, 'name': 'Max', 'three': 4}
is_admin = data.get('admin', False)

Get a subset of the list

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

x = [1,2,3,4,5,6]
#First 3
print x[:3]
>>> [1,2,3]
#4 in the middle
print x[1:5]
>>> [2,3,4,5]
#The last 3
print x[-3:]
>>> [4,5,6]
#Odd term
print x[::2]
>>> [1,3,5]
#Even number
print x[1::2]
>>> [2,4,6]

60 characters to solve FizzBuzz

A few days ago, Jeff Atwood promoted a simple programming exercise called FizzBuzz. The questions are as follows:

Write a program to print "Fizz" in multiples of numbers 1 to 100, 3 to replace this number, 5 to print "Buzz", and print "FizzBuzz" in multiples of both 3 and 5.

Here is a short and 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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In addition to python's built-in data types, the collection module also includes some special use cases, and Counter is very practical in some cases. If you've ever been to Facebook hacker Cup this year, you can even find out where it works.

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

Iterative tool

Like the collections library, there is also a library called itertools, which can effectively solve some problems. One of the use cases is to find all combinations. It can tell you all the impossible 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 an interesting thing compared to practical technology. In python, True and False are global variables, so

False = True
if False:
 print "Hello"
else:
 print "World"
>>> Hello
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Posted on Mon, 10 Feb 2020 07:46:41 -0800 by inversesoft123