2.23 Summary - dictionaries, assignments

1. Cognitive Dictionary (dict)

1. Is a container data type; Take {} as the flag of the container, in which multiple key value pairs are separated by commas: {key 1: value 1, key 2: value 2, key 3: value 3,...}
   Key value pair: key value

2. The dictionary is changeable (support addition, deletion and modification); The dictionary is out of order (subscripts are not supported, and the order of elements does not affect the result)

3. Requirements for elements
   Dictionary elements are key value pairs
   a. Key requirements: the key must be immutable type of data (data, string, Boolean, tuple, etc.); Key is unique
   b. Value requirement: no requirement

2. Look up - get the value of the dictionary

1. Check single (important) - get one value at a time

   Syntax 1: Dictionary [key] - get the value corresponding to the specified key in the dictionary; If the key does not exist, an error will be reported

   Syntax 2:
   Dictionaries. Get (key) - get the value corresponding to the specified key in the dictionary; If the key does not exist, no error will be reported and None will be returned
   Dictionaries. Get (key, default value) - get the value corresponding to the specified key in the dictionary; If the key does not exist, the default value is returned

2. ergodic

   1) Direct traversal
   for key in Dictionary:
   pass

   for key, value in dictionary items():
   pass

3. Add, modify - add key value pair

   1. DICTIONARY [key] = value. If the key exists, modify the value corresponding to the specified key; If the key does not exist, add a key value pair
   2. Dictionaries. SetDefault (key, value) add a key value pair (if the key does not exist, add a key value pair; if the key exists, do not move the dictionary)

4. Delete - delete key value pairs

   del DICTIONARY [key] - delete the key value pair corresponding to the specified key
   Dictionaries. Pop (key) - take out the value corresponding to the specified key

5. Related operation

   1) Operator: dictionary does not support: +, *, >, <, > =, < =, only = ==
   2)in and not in - the in and not in operations of the dictionary determine whether the specified key exists in the dictionary
   Key in dictionary

   3) Correlation function: len, dict

   Len (Dictionary) - get the number of key value pairs in the dictionary

   Dict (data) - converts the specified data into a dictionary
   Requirements for data: 1 The data itself is a sequence
   2. The elements in the sequence must be a small sequence with only two elements, and the first element is immutable data

   4) Related methods

   a. Dictionary clear()
   b. Dictionary copy()
   c.
   Dictionaries. keys() - returns a sequence in which the elements are all the keys of the dictionary
   Dictionaries. values() - returns a sequence in which the elements are all the values of the dictionary
   Dictionaries. items() - returns a sequence in which elements are tuples of keys and values

   d. update
   Dictionaries. Update (sequence) - add all the elements in the sequence to the dictionary (the sequence must be a sequence that can be converted into a dictionary)
   Dictionary 1 Update (dictionary 2) - add all key value pairs in dictionary 2 to dictionary 1

6. Dictionary derivation

{expression 1: expression 2 for variable in sequence}

{expression 1: expression 2 for variable in sequence if conditional statement}

task

1. Define a variable to save a student's information. Student confidence includes: name, age, grade (single subject), telephone and gender

   dict1 = {
       'name': 'Xiao Ming',
       'age': 18,
       'score': 66,
       'tel': '15579927163',
       'gender': 'male'
   }
   

2. Define a list and save the information of 6 students in the list (student information includes: name, age, grade (single subject), telephone, gender (male, female, unknown))

   stu = [
           {'name': 'Xiao Ming', 'age': 18, 'score': 100, 'tel': '132456', 'gender': 'male'},
           {'name': 'floret', 'age': 25, 'score': 98,  'tel': '132874', 'gender': 'female'},
           {'name': 'Zhang San', 'age': 34, 'score': 90,  'tel': '123428', 'gender': 'male'},
           {'name': 'Li Si', 'age': 18, 'score': 70,  'tel': '947322', 'gender': 'Gender unknown'},
           {'name': 'WangTwo ', 'age': 19, 'score': 55,  'tel': '346741', 'gender': 'male'},
           {'name': 'Zhao Min', 'age': 18, 'score': 99,  'tel': '473669', 'gender': 'female'},
           {'name': 'Lao Wang', 'age': 16, 'score': 43,  'tel': '132124', 'gender': 'male'}
   ]
   print(stu)
   

   1. Count the number of failed students

      count1 = 0
      for i in stu:
          if i['score'] < 60:
              count1 += 1
      print(count1)
      

   2. Print the name of the failed minor student and the corresponding score

      for i in stu:
          if i['score'] < 60 and i['age'] < 18:
              print(i['name'],i['score'])
      

   3. Find the average age of all boys

      otal_age = 0
      for i in stu:
          total_age += i['age']
      print(total_age/len(stu))
      

   4. The student's name printed at the end of the mobile phone is 8

      name1 = [i['name'] for i in stu if i['tel'][-1] == '8']
      print(name1)
      

   5. Print the highest score and the corresponding student's name

      max_score = stu[0]['score']
      max_name = [stu[0]['name']]
      for i in stu[1:]:
          if i['score'] > max_score:
              max_score = i['score']
              max_name.clear()
              max_name.append(i['name'])
          elif i['score'] == max_score:
              max_name.append(i['name'])
      print(max_score, max_name)
      

   6. Delete all students of Unknown Gender

      for x in stu[:]:
          if x['gender'] == 'Gender unknown':
              stu.remove(x)
      print(stu)
      

   7. Sort the list according to the students' grades from big to small (struggle, give up if you can't)

      list1 =[stu[0]]
      for i in stu[1:]:
          for index, item in enumerate(list1):
              print(index, item)
              if i['score'] >= item['score']:
                  list1.insert(index, i)
                  break
          else:
              list1.append(i)
      print(list1)
      

3. Define a variable to save the information of a class. The class information includes: class name, classroom location, head teacher information, lecturer information and all students in the class (determine the data type and specific information according to the actual situation)

   class1 = {
       'class_name': 'python2201',
       'address': '12 classroom',
       'class_teacher': {'name': 'Rui Yan Zhang', 'gender': 'female', 'tel': '1221421'},
       'lecturer': {'name': 'Yu Ting', 'gender': 'female', 'tel': '13678192302'},
       'students': [
           {'name': 'Xiao Ming', 'gender': 'male', 'age': 18, 'score': 100, 'education': 'specialty', 'linkman': {'name': 'Xiao Wu', 'tel': '110'}},
           {'name': 'floret', 'gender': 'female', 'age': 20, 'score': 98, 'education': 'undergraduate', 'linkman': {'name': 'Xiao Zhang', 'tel': '120'}},
           {'name': 'Zhang San', 'gender': 'male', 'age': 30, 'score': 90, 'education': 'undergraduate', 'linkman': {'name': 'Xiao Zhao', 'tel': '119'}},
           {'name': 'Li Si', 'gender': 'male', 'age': 22, 'score': 70, 'education': 'specialty', 'linkman': {'name': 'Xiao Liu', 'tel': '134'}},
           {'name': 'WangTwo ', 'gender': 'male', 'age': 28, 'score': 95, 'education': 'undergraduate', 'linkman': {'name': 'Xiao Xu', 'tel': '2383'}},
           {'name': 'Zhao Min', 'gender': 'female', 'age': 27, 'score': 99, 'education': 'specialty', 'linkman': {'name': 'Xiao Hu', 'tel': '23423'}},
           {'name': 'Lao Wang', 'gender': 'male', 'age': 22, 'score': 89, 'education': 'undergraduate', 'linkman': {'name': 'Xiao Wang', 'tel': '1234'}}
       ]
   }
   

4. It is known that a list stores dictionaries corresponding to multiple dogs:

   dogs = [
     {'name': 'Beibei', 'color': 'white', 'breed': 'Silver Fox', 'age': 3, 'gender': 'mother'},
     {'name': 'tearful', 'color': 'grey', 'breed': 'FA Dou', 'age': 2},
     {'name': 'Caicai', 'color': 'black', 'breed': 'Earth dog', 'age': 5, 'gender': 'common'},
     {'name': 'steamed stuffed bun', 'color': 'yellow', 'breed': 'Siberian Husky', 'age': 1},
     {'name': 'cola', 'color': 'white', 'breed': 'Silver Fox', 'age': 2},
     {'name': 'Wangcai', 'color': 'yellow', 'breed': 'Earth dog', 'age': 2, 'gender': 'mother'}
   ]
   

   1. Use the list derivation to obtain the breeds of all dogs

      ['silver fox', 'fadou', 'earth dog', 'husky', 'silver fox', 'earth dog']

      breed1 = [dog['breed'] for dog in dogs]
      print(breed1)
      

   2. Use list derivation to get the names of all white dogs

      ['Beibei', 'Coke']

      name1 = [dog['name'] for dog in dogs if dog['color'] == 'white']
      print(name1)
      

   3. Add "male" to dogs without gender in dogs

      for dog in dogs:
          dog.setdefault('gender', 'common')
      print(dogs)
      

   4. Count the number of 'silver foxes'

      count1 = len([dog for dog in dogs if dog['breed'] == 'Silver Fox'])
      print(count1)