《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])