python中的列表和字典(二)

三. 字典以及相关使用

1. 字典的定义 dict{}

2. 字典特征：字典是无序的，key-value键值对形式，key值不重复

3. 字典的赋值：dictA = {keyA: valueA, keyB: valueB, keyC: valueC}

4. 字典的取值：dictA[keyA]  dictA.get(keyA)

5. 字典的所有键：dictA.keys()      key-value获取：dictA.items()

6. 修改字典中元素的值：dictA[keyA] = value

7. 获取字典的长度：len(dictA)

8. 字典中添加元素：dictA[key_new] = value

9. 删除字典所有元素：dictA.clear()

10. 删除整个字典：del dictA

11. 字典组合：dict(dictA, **dictB)      dictA.update(dictB)

四. 实例

1. 字典的定义，字典的键名只能是数字、字符串、元组，且不能重复

stu1 = {"name": "Mr.逗", "sex": "male", "age": 20, "hobby": "run"}
print(stu1)


结果：
{'sex': 'male', 'hobby': 'run', 'name': 'Mr.逗', 'age': 20}

2. 字典取值：dictA[keyA]  dictA.get(keyA)

stu1 = {"name": "Mr.逗", "sex": "male", "age": 20, "hobby": "run"}
print(stu1["name"])
print(stu1.get("name"))


结果:
Mr.逗
Mr.逗

3. 修改字典值：dictA[keyA] = value，keyA是已存在的key

stu1 = {"name": "Mr.逗", "sex": "male", "age": 20, "hobby": "run"}
stu1["name"] = "Mr.小小逗"
print(stu1)


结果：
{'hobby': 'run', 'age': 20, 'name': 'Mr.小小逗', 'sex': 'male'}

4. 向字典中添加键值对，dictA[key_new] = value，key_new是不存在的

stu1 = {"name": "Mr.逗", "sex": "male", "age": 20, "hobby": "run"}
stu1["study"] = "python"


结果:
{'age': 20, 'study': 'python', 'name': 'Mr.逗', 'sex': 'male', 'hobby': 'run'}

5. 获取字典的长度：len(dictA)

stu1 = {"name": "Mr.逗", "sex": "male", "age": 20, "hobby": "run"}
print(len(stu1))


结果:
4

6. 两个字典的组合：dictA.update(dictB)  dict(dictA, **dictB) 

B = {"name": "xiaojian", "age": 28, "is_marry": False}
B.update({"role": "teacher", "class": "python"})
print(B)


结果:
{'class': 'python', 'is_marry': False, 'age': 28, 'role': 'teacher', 'name': 'xiaojian'}

B = {"name": "xiaojian", "age": 28, "is_marry": False}
C = {"role": "teacher", "class": "python"}
D = dict(B, **C)
print(D)


结果:
{'class': 'python', 'is_marry': False, 'age': 28, 'role': 'teacher', 'name': 'xiaojian'}

7. 删除字典中所有元素：dictA.clear()，只是清空字典

a = {"name": "Jack", "sex": "M"}
a.clear()
print(a)


结果:
{}

8. 删除整个字典：del dictA

a = {"name": "Jack", "sex": "M"}
del a
print(a)


结果:
Traceback (most recent call last):
  File "<pyshell#5>", line 1, in <module>
    print(a)
NameError: name 'a' is not defined