给Python初学者的一些编程技巧

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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]

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

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

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