《Python for Beginners》学习笔记（6）

《Python for Beginners》为LearnStreet上的Python入门课程。本节主要学习内容为Dictionaries(字典)。

Lesson 7 Dictionaries

1. Indexing Dictionaries
查找字典练习

1 def run():
2     family = {"dad": 60, "mom" : 58, "brother": 20, "sister" : 15, "me" : 10}
3     return family["brother"]
4 
5 #This is just for you to see what happens when the function is called
6 print run()

输出结果：
20

2. Creating Dictionaries
创建字典

1 def run():
2     knights = {"Arthur": "king", "Lancelot": "brave", "Galahad": "pure", "Robin": "not-quite-so-brave"}
3     return knights
4 
5 #This is just for you to see what happens when the function is called
6 print run()

输出结果：
{'Arthur': 'king', 'Galahad': 'pure', 'Robin': 'not-quite-so-brave', 'Lancelot': 'brave'}

3. Adding to Dictionaries
为字典添加元素

You can add a key/value pair to a dictionary with this syntax: dictionary_name[key] = value.

1 def run():
2     knights = {"Arthur":"king", "Lancelot":"brave", "Galahad":"pure", "Robin":"not-quite-so-brave"}
3     knights["Bedivere"] = "wise"
4     return knights
5 
6 #This is just for you to see what happens when the function is called
7 print run()

输出结果：
{'Arthur': 'king', 'Galahad': 'pure', 'Bedivere': 'wise', 'Robin': 'not-quite-so-brave', 'Lancelot': 'brave'}

4. Deleting from Dictionaries
从字典中删除一个元素。

1 def run():
2     knights = {"Arthur":"king", "Lancelot":"brave", "Galahad":"pure", "Robin":"not-quite-so-brave", "Bedivere":"wise"}
3     #your code here
4     del knights["Galahad"]
5     return knights
6 
7 #This is just for you to see what happens when the function is called
8 print run()

输出结果：
{'Arthur': 'king', 'Bedivere': 'wise', 'Robin': 'not-quite-so-brave', 'Lancelot': 'brave'}

5. Iterating

 1 >>> def run(letters):
 2     keys = []
 3     values = []
 4     #your code here
 5     for key in letters.keys():
 6         keys.append(key)
 7     for value in letters.values():
 8         values.append(value)
 9     return (keys, values)
10 
11 >>> print run({"a": 1, "b": 2, "c": 3, "d": 4})
12 (['a', 'c', 'b', 'd'], [1, 3, 2, 4])

6. 复习
任务：Combine the two dictionaries into family and remove both exes. Don't forget to return family at the end.

 1 >>> def run():
 2      smiths = {"father": "Mike", "ex-wife" : "Mary", "children" : ["Bobby", "Susan"] }
 3      jones = {"mother": "Lucy", "ex-husband": "Peter", "children": ["Michelle", "Jeff", "Evan"]}
 4      family = {}
 5      for key in smiths:
 6          if key in family:
 7              family[key]+=smiths[key]
 8          else:
 9              family[key]=smiths[key]
10      for key in jones:
11          if key in family:
12              family[key]+=jones[key]
13          else:
14              family[key]=jones[key]
15      keysToDel = []
16      for key in family:
17          if 'ex' in key:
18              keysToDel.append(key)
19      print keysToDel
20      for key in keysToDel:
21          del family[key]
22      return family
23 
24 >>> print run()
25 ['ex-husband', 'ex-wife']
26 {'father': 'Mike', 'children': ['Bobby', 'Susan', 'Michelle', 'Jeff', 'Evan'], 'mother': 'Lucy'}

7. Set Operations
计算两个集合的交集。

1 >>> def run(first, second):
2     #your code here
3     return first.intersection(second)
4 
5 >>> run(set(range(11)), set(range(4)))
6 set([0, 1, 2, 3])

8. Creating Sets
创建两个集合，并求它们的并集。

1 >>> def run():
2     set1 = {4, 6, 7, 9, 10, 12}
3     set2 = {6, 9, 10, 12, 20}
4     return set1.union(set2)
5 
6 >>> print run()
7 set([4, 6, 7, 9, 10, 12, 20])