交換變量
- x = 6
- y = 5
- x, y = y, x
- print x
- >>> 5
- print y
- >>> 6
- print "Hello" if True else "World"
- >>> Hello
連接 下面的最後一種方式在綁定兩個不同類型的對象時顯得很cool。
- 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
- #除後向下取整
- 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'
我承認try/except代碼並不雅緻,不過這裏有一種簡單方法,嘗試在字典中查找key,如果沒有找到對應的alue將用第二個參數設爲其變量值。
- data = {'user': 1, 'name': 'Max', 'three': 4}
- try:
- is_admin = data['admin']
- except KeyError:
- is_admin = False
- data = {'user': 1, 'name': 'Max', 'three': 4}
- is_admin = data.get('admin', False)
- x = [1,2,3,4,5,6]
- #前3個
- print x[:3]
- >>> [1,2,3]
- #中間4個
- print x[1:5]
- >>> [2,3,4,5]
- #最後3個
- print x[3:]
- >>> [4,5,6]
- #奇數項
- print x[::2]
- >>> [1,3,5]
- #偶數項
- print x[1::2]
- >>> [2,4,6]
前段時間Jeff Atwood 推廣了一個簡單的編程練習叫FizzBuzz,問題引用如下:
寫一個程序,打印數字1到100,3的倍數打印“Fizz”來替換這個數,5的倍數打印“Buzz”,對於既是3的倍數又是5的倍數的數字打印“FizzBuzz”。這裏就是一個簡短的,有意思的方法解決這個問題:
- for x in range(101):print"fizz"[x%3*4::]+"buzz"[x%5*4::]or x
除了python內置的數據類型外,在collection模塊同樣還包括一些特別的用例,在有些場合Counter非常實用。如果你參加過在這一年的Facebook HackerCup,你甚至也能找到他的實用之處。
- from collections import Counter
- print Counter("hello")
- >>> Counter({'l': 2, 'h': 1, 'e': 1, 'o': 1})
和collections庫一樣,還有一個庫叫itertools,對某些問題真能高效地解決。其中一個用例是查找所有組合,他能告訴你在一個組中元素的所有不能的組合方式
- 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')
比起實用技術來說這是一個很有趣的事,在python中,True和False是全局變量,因此:
- False = True
- if False:
- print "Hello"
- else:
- print "World"
- >>> Hello