Python_7_Codecademy_7_Lists, For Loop and Dictionaries

总目录

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课程页面：https://www.codecademy.com/
内容包含课程笔记和自己的扩展折腾

Lists

• 例如：list_sample = [1, 2, 3, "ZHANG Yong", "张雍"]
• 和string一样，可以是空的：[]
• 和string一样，也有index，从0开始。
  print list_sample[4] Output: 张雍
• 可以替换list里面的items，譬如把sample list里面的3换成"ZY"：
  list_sample[2] = "ZY"
• 增加 item： .append():
  list_sample.append(6) # [1, 2, 3, "ZHANG Yong", "张雍", 6]
• 和string一样，也有长度：len()
• 和string一样，也能部分获取： list_sample[n:m]
• 询问index: list.index(item) 譬如询问"张雍"的index：
  print list_sample.index("张雍") Output: 4
• 插入指定位置： list.insert(index, item)

list_sample = [1, 2, 3, "ZHANG Yong", "张雍"]
list_sample.insert(1, 1.5)
# 就变成了：[1, 1.5, 2, 3, "ZHANG Yong", "张雍"]

• 排序：list.sort()

#sort list_A in alphabetical order
list_A = ["cool", "astronaut", "zebra", "xenophobia", "recursive"]
list_A.sort()
print list_A

Output:
['astronaut', 'cool', 'recursive', 'xenophobia', 'zebra']

• **移除item(s): ** list.remove(item)

list_A = ["cool", "astronaut", "zebra", "xenophobia", "recursive"]
list_A.remove("cool")
print list_A

Output:
['astronaut', 'zebra', 'xenophobia', 'recursive']

For loop

例0：String Looping
string也是可以loop的：

for x in "ZHANG_Yong"
    print x

Output:
Z
H
A
N
G
_
Y
o
n
g
Process finished with exit code 0

例1：打印出列表中都有哪些items：

list_sample = [1, 2, 3, "ZHANG Yong", "张雍"]
for x in list_sample:
  print "%s is in this list" % x

Output:
1 is in this list
2 is in this list
3 is in this list
ZHANG Yong is in this list
张雍 is in this list

例2：listA是数字，输出其平方，且按照大小排序：

listA = [6, 7, 1, 9, 0]
listB = []
for x in listA:
  listB.append(x**2)
listB.sort()
print listB

Output:
[0, 1, 36, 49, 81]

例3：多个lists作为arguments

list_A = [3, 9, 17, 15, 19]
list_B = [2, 4, 8, 10, 30, 40, 50, 60, 70, 80, 90]
for a, b in zip(list_A, list_B):
    print max(a, b)

Console:
3
9
17
15
30

Dictionaries

• 和string&list一样，可以是空的：{}
• key-value pairs / tuples: 然后就能通过比较好记的key拿到对应的value
  {key : value, key2 : value2, ...}

d = {"birthday_day" : "1st", "birthday_month" : "June"}
print d["birthday_day"]

Output:
1st

• 增加tuples: (和往list里面加items类似）
  dictionary[new_key] = new_value

d = {"birthday_day" : "1st", "birthday_month" : "June"}
d["fav_fruit"] = "orange"
print d

Output:
{'birthday_month': 'June', 'birthday_day': '1st', 'fav_fruit': 'orange'}

• value可以是list:

d = {"birthday_day" : "1st", "birthday_month" : "June"}
d["fav_fruit"] = ["orange", "avocado", "banana"]
print d

Output:
{'birthday_month': 'June', 'birthday_day': '1st', 'fav_fruit': ['orange', 'avocado', 'banana']}

• **len(d): **多少个tuples
• 删除tuple： del dictionary[key]
• 更改value： `dictionary[key] = new_value
• curly braces 之间可以断行：

d = {
    'birthday_month': 'June', 
    'birthday_day': '1st', 
    'fav_fruit': ['orange', 'avocado', 'banana']
}

• grab an item from a list in a dictionary

# grab my first two fav food
d = {
    'birthday_month': 'June', 
    'birthday_day': '1st', 
    'fav_fruit': ['orange', 'avocado', 'banana']
}
print d["fav_fruit"][:2]

Output:
['orange', 'avocado']

• for loop and dictionary:

d = {
    'fav_fruit': ['orange', 'avocado', 'banana'],
    'birthday_month': 'June', 
    'birthday_day': '1st', 
}
# 注意上面dictionary里面tuples的顺序
for x in d:
    print x + ":", d[x] 

Output:
birthday_month: June
birthday_day: 1st
fav_fruit: ['orange', 'avocado', 'banana']
注意这里的顺序