Python初學者的17個技巧

標籤：python   初學者   

交換變數

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

if 語句在行內

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

串連

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酷。

nfc = ["Packers", "49ers"]afc = ["Ravens", "Patriots"]print nfc + afc>>> [‘Packers‘, ‘49ers‘, ‘Ravens‘, ‘Patriots‘]print str(1) + " world">>> 1 worldprint `1` + " world">>> 1 worldprint 1, "world">>> 1 worldprint nfc, 1>>> [‘Packers‘, ‘49ers‘] 1

計算技巧

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

注意浮點數的除法

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

數值比較

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

兩個列表同時迭代

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

帶索引的列表迭代

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

列表推導

已知一個列表，刷選出偶數列表方法：

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

用下面的代替

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

字典推導

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

初始化列表的值

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

將列錶轉換成字串

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

從字典中擷取元素

不要用下列的方式

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

替換為

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

擷取子列表

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]

譯文出處：Python初學者的17個技巧

Python初學者的17個技巧