Dictionary type built-in method (dict)
- 1. Purpose: a plurality of stored values, but each has a value of a corresponding key, key values described functions. It is used for different states when the stored value indicates, for example, the value stored there name, age, height, weight, hobbies.
* 2 definitions: {} within the plurality of elements spaced apart by commas, each element is a key: in the form of value, the data value may be any type, but generally should be a string type key, but the key must be immutable Types of.
dic = {'a': 1, 'b': 2} # dic = dict({'a':1,'b':2})
print(f"dic: {dic}")dic: {'a': 1, 'b': 2}
dic = dict(a=1, b=2, c=3)
print(f"dic: {dic}")dic: {'a': 1, 'b': 2, 'c': 3}
dic = {1: 'a', 0: 'b'}
print(f"dic[0]: {dic[0]}") # 无法区分dic是列表，还是字典，并且key不再具有描述信息dic[0]: b
dic = {[1,2]: 'a', 0: 'b'} # 报错- 3. common operations + built-in method: built-in methods and common operations are divided into priority master (today have to remember), need to know (remember the week) in two parts.
Priority control (*****)
1. Press the key access Found: can be stored preferably
2. length len
3. members in operation in and Not
4. Remove del
5. The button keys (), the value of values (), on the key-value items ()
6. The loop
1. access key press value: deposit may be desirable
# dic之按key存取值
dic = {'a': 1, 'b': 2}
print(f"first dic['a']: {dic['a']}")
dic['a'] = 3
print(f"second dic['a']: {dic['a']}")first dic['a']: 1 second dic['a']: 3
2. length len
# dic之长度len
dic = {'a': 1, 'b': 2}
print(f"len(dic): {len(dic)}")len(dic): 2
3. The members of the operations in and not in
# dic之成员运算in和not in
dic = {'a': 1, 'b': 2}
print(f"'a' in dic: {'a' in dic}")
print(f"1 in dic: {1 in dic}")'a' in dic: True 1 in dic: False
4. Delete
# dic之删除del
dic = {'a': 1, 'b': 2}
del dic['a']
print(f"dic.get('a'): {dic.get('a')}")dic.get('a'): None
# dic之删除pop()
dic = {'a': 1, 'b': 2}
dic.pop('a') # 指定元素删除
print(f"dic.pop('b'): {dic.pop('b')}")
print(f"dic.get('a'): {dic.get('a')}")dic.pop('b'): 2 dic.get('a'): None
# dic之删除popitem()
dic = {'a': 1, 'b': 2}
print(f"dic.popitem(): {dic.popitem()}") # 随机删除一个元素，无法指定dic.popitem(): ('b', 2)
The key keys (), the value of values (), on the key-value items ()
# dic之键keys()、值values()、键值对items()，python2中取出的是列表（鸡蛋）；python3中取出的是元组（鸡）
dic = {'a': 1, 'b': 2}
print(f"dic.keys(): {dic.keys()}")
print(f"dic.values(): {dic.values()}")
print(f"dic.items(): {dic.items()}")dic.keys(): dict_keys(['a', 'b']) dic.values(): dict_values([1, 2]) dic.items(): dict_items([('a', 1), ('b', 2)])
6. cycle
# dic之循环
# dic是无序的，但是python3采用了底层优化算法，所以看起来是有序的，但是python2中的字典是无序
dic = {'a': 1, 'b': 2, 'c': 3, 'd': 4}
for k, v in dic.items(): # items可以换成keys()、values()
print(k, v)a 1 b 2 c 3 d 4
Need to know
1.get
update
fromkeys
setdefault
1.get()
# dic之get()
dic = {'a': 1, 'b': 2}
print(f"dic.get('a'): {dic.get('a')}")
print(f"dic.get('c'): {dic.get('c')}")dic.get('a'): 1 dic.get('c'): None
2.update()
# dic之update()
dic1 = {'a': 1, 'b': 2}
dic2 = {'c': 3}
dic1.update(dic2)
print(f"dic1: {dic1}")dic1: {'a': 1, 'b': 2, 'c': 3}
3.fromkeys()
# dic之fromkeys()
dic = dict.fromkeys(['name', 'age', 'sex'], None)
print(f"dic: {dic}")dic: {'name': None, 'age': None, 'sex': None}
4.setdefault()
# dic之setdefault()，有指定key不会改变值；无指定key则改变值
dic = {'a': 1, 'b': 2}
print(f"dic.setdefault('a'): {dic.setdefault('a',3)}")
print(f"dic: {dic}")
print(f"dic.setdefault('c'): {dic.setdefault('c',3)}")
print(f"dic: {dic}")dic.setdefault('a'): 1 dic: {'a': 1, 'b': 2} dic.setdefault('c'): 3 dic: {'a': 1, 'b': 2, 'c': 3}
Stored value or a plurality of values:
A plurality of values, the value may be a plurality of types, key must be immutable type, generally should be immutable types string type