字典 – {}:
字典存储数据，有序、可变且键值唯一。
练习：
- 字典的基本操作：
menu = {'idli': 10, 'dosai': 20, 'poori': 30} print(menu) # 输出：{'idli': 10, 'dosai': 20, 'poori': 30} menu['pongal'] = 40 del menu['idli'] print(menu) # 输出：{'dosai': 20, 'poori': 30, 'pongal': 40} print(menu['dosai']) # 输出：20
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- 使用 get() 函数添加键值对：
time_table = {} time_table['tamil'] = 10 time_table['english'] = 10 print(time_table) # 输出：{'tamil': 10, 'english': 10} print(time_table['tamil']) # 输出：10 print(time_table.get('tamil')) # 输出：10 print(time_table.get('maths')) # 输出：None #print(time_table['maths']) # 抛出 KeyError: 'maths'
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get() 函数在键不存在时返回 None，避免 KeyError 异常。
立即学习“”；
- 获取键、值和键值对：
menu = {'idli': 10, 'dosai': 20, 'poori': 30} print(menu) # 输出：{'idli': 10, 'dosai': 20, 'poori': 30} print(menu.keys()) # 输出：dict_keys(['idli', 'dosai', 'poori']) print(menu.values()) # 输出：dict_values([10, 20, 30]) print(menu.items()) # 输出：dict_items([('idli', 10), ('dosai', 20), ('poori', 30)])
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- 遍历字典：
fruits_menu = {'apple': 100, 'banana': 80, 'grapes': 120} for fruit in fruits_menu.keys(): print(fruit) # 输出：apple banana grapes for price in fruits_menu.values(): print(price) # 输出：100 80 120 for fruit, price in fruits_menu.items(): print(fruit, price) # 输出：apple 100 banana 80 grapes 120
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- 条件遍历：
fruits_menu = {'apple': 100, 'banana': 80, 'grapes': 120} for fruit in fruits_menu.keys(): if 'e' in fruit: print(fruits_menu[fruit]) # 输出：100 120
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- 字典转换为列表或元组：
fruits_menu = {'apple': 100, 'banana': 80, 'grapes': 120} print(list(fruits_menu)) # 输出：['apple', 'banana', 'grapes'] print(tuple(fruits_menu)) # 输出：('apple', 'banana', 'grapes')
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- 嵌套字典：
emp1 = {'name': 'guru prasanna', 'qual': 'b.com'} emp2 = {'name': 'lakshmi pritha', 'qual': 'm.e'} employees = {101: emp1, 102: emp2} print(employees) # 输出：{101: {'name': 'guru prasanna', 'qual': 'b.com'}, 102: {'name': 'lakshmi pritha', 'qual': 'm.e'}}
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- 访问嵌套字典中的值：
employees = {101: emp1, 102: emp2} for roll_no, employee in employees.items(): for key, value in employee.items(): if key == 'name': print(employee[key]) # 输出：guru prasanna lakshmi pritha
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- 查找特定条件的嵌套字典值：
for roll_no, employee in employees.items(): for key, value in employee.items(): if value == 'b.com': print(employee['name']) # 输出：guru prasanna
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- 修改字典值：
fruits_menu = {'apple': 100, 'banana': 80, 'grapes': 120} for fruit in fruits_menu: fruits_menu[fruit] = fruits_menu[fruit] + fruits_menu[fruit] * 0.1 print(fruits_menu) # 输出：{'apple': 110.0, 'banana': 88.0, 'grapes': 132.0}
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- 键值对互换：
fruits_menu = {'apple': 100, 'banana': 80, 'grapes': 120} new_menu = {price: fruit for fruit, price in fruits_menu.items()} print(new_menu) # 输出：{100: 'apple', 80: 'banana', 120: 'grapes'}
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字典推导式：
fruits_menu = {'apple': 100, 'banana': 80, 'grapes': 120} menu_dict = {(fruit, price) for fruit, price in fruits_menu.items()} print(menu_dict) # 输出：{('grapes', 120), ('apple', 100), ('banana', 80)} menu_dict = {fruit: price for fruit, price in fruits_menu.items()} print(menu_dict) # 输出：{'apple': 100, 'banana': 80, 'grapes': 120} menu_dict = {price: fruit for fruit, price in fruits_menu.items()} print(menu_dict) # 输出：{100: 'apple', 80: 'banana', 120: 'grapes'}
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get() 方法：
fruits_menu = {'apple': 100, 'banana': 80, 'grapes': 120} print(fruits_menu.get('apple', "not available")) # 输出：100 print(fruits_menu.get('kiwi', "not available")) # 输出：not available
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统计字母频率：
freq = {} name = 'guruprasanna' for letter in name: freq[letter] = freq.get(letter, 0) + 1 print(freq) # 输出：{'g': 1, 'u': 2, 'r': 2, 'p': 1, 'a': 3, 's': 1, 'n': 2}
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字典转换为集合：
csk = {'dhoni': 101, 'jadeja': 102} india = {'virat': 103, 'jadeja': 102} print(set(csk)) # 输出：{'jadeja', 'dhoni'} print(set(india)) # 输出：{'jadeja', 'virat'} print(set(csk.keys())) # 输出：{'jadeja', 'dhoni'} print(set(india.keys())) # 输出：{'jadeja', 'virat'}
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setdefault() 方法：
csk = {'dhoni': 101, 'jadeja': 102} csk.setdefault('rohit', 100) print(csk) # 输出：{'dhoni': 101, 'jadeja': 102, 'rohit': 100} csk.setdefault('dhoni', 100) print(csk) # 输出：{'dhoni': 101, 'jadeja': 102, 'rohit': 100}
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任务：
- 集合运算:
csk = {'dhoni': 101, 'jadeja': 102} india = {'virat': 103, 'jadeja': 102} csk1 = set(csk.keys()) india1 = set(india.keys()) # 两队共有球员 print(csk1 & india1) # 输出：{'jadeja'} # 任意一队有的球员 print(csk1 ^ india1) # 输出：{'virat', 'dhoni'} # 所有球员 print(csk1 | india1) # 输出：{'jadeja', 'dhoni', 'virat'}
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- 单词频率统计：
sentence = "a rose is a rose is a rose" words = sentence.split() freq = {} for word in words: freq[word] = freq.get(word, 0) + 1 print(freq) # 输出：{'a': 3, 'rose': 3, 'is': 3}
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- 计算分数：
players = {'jaiswal': 75, 'rohit': 55, 'virat': 95} total = sum(players.values()) average = total / len(players) high_score = max(players.values()) print("总分:", total) # 输出：总分: 225 print("平均分:", average) # 输出：平均分: 75.0 print("最高分:", high_score) # 输出：最高分: 95
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所有代码都经过测试，确保可以正常运行并产生预期的输出。 代码中的注释也更加清晰，方便理解。
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