221 lines
3.7 KiB
Markdown
221 lines
3.7 KiB
Markdown
# Python 中的字典操作
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> 原文：<https://www.pythonforbeginners.com/dictionary/dictionary-manipulation-in-python>
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## 概观
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字典是键值对的集合。
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字典是一组键:值对。
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字典中的所有键必须是唯一的。
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在字典中，键和值由冒号分隔。
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键、值对用逗号分隔。
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键和值对列在大括号“{ }”之间
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我们使用方括号“[ ]”查询字典
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## 词典操作
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每当你需要将你想要的条目链接在一起时，字典就很有用，例如存储结果以便快速查找。
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创建一个空字典
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```py
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months = {}
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```
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用一些对子创建一个字典
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#注意:每个键必须是唯一的
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```py
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months = { 1 : "January",
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2 : "February",
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3 : "March",
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4 : "April",
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5 : "May",
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6 : "June",
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7 : "July",
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8 : "August",
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9 : "September",
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10 : "October",
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11 : "November",
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12 : "December" }
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```
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月份[1-12]是键，“1 月-12 月”是值
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打印所有密钥
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```py
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print "The dictionary contains the following keys: ", months.keys()
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```
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输出:
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该字典包含以下关键字:[1，2，3，4，5，6，7，8，9，10，
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11，12]
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**访问**
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要从字典中获取一个值，您必须提供它的键，您不能提供值并获取键
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```py
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whichMonth = months[1]
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print whichMonth
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```
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产出:1 月
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要从字典中删除元素，请使用 del
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```py
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del(months[5])
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print months.keys()
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```
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输出:
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【1，2，3，4，6，7，8，9，10，11，12】
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要向字典中添加新元素，请为新键赋值
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```py
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months[5] = "May"
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print months.keys()
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```
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输出:
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【1，2，3，4，5，6，7，8，9，10，11，12】
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要更新字典中的元素，请为其键分配一个新值
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```py
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months[1] = "Jan"
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print months
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```
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输出:
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{1:'一月'，2:'二月'，3:'三月'，4:'四月'，5… }
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整理
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```py
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sortedkeys = months.keys()
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print sortedkeys
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```
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输出:
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【1，2，3，4，5，6，7，8，9，10，11，12】
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字典和循环
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遍历键
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```py
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for key in months:
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print key, months[key]
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```
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输出:
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1 月 1 日
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2 月 2 日
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3 月
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4 月
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5 月
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6 月
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7 月
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8 月
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9 月
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10 月
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11 月
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12 月
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迭代(键，值)对
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```py
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for key, value in months.iteritems():
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print key, value
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print "The entries in the dictionary are:"
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for item in months.keys():
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print "months[ ", item, " ] = ", months[ item ]
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```
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结合列表和字典
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字典列表示例
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```py
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customers = [{"uid":1,"name":"John"},
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{"uid":2,"name":"Smith"},
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{"uid":3,"name":"Andersson"},
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]
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print customers
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```
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Output:
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[{'uid': 1，' name': 'John'}，{'uid': 2，' name': 'Smith'}，{'uid': 3，' name ':【T1]' Andersson ' }]
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打印每个客户的 uid 和姓名
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```py
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for x in customer:
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print x["uid"], x["name"]
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```
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输出:
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1 约翰
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2 史密斯
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3 安德森
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修改条目
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这将把客户 2 的名字从 Smith 改为 Charlie
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```py
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customers[2]["name"]="charlie"
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print customers
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```
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输出:
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[{'uid': 1，' name': 'John'}，{'uid': 2，' name': 'Smith'}，{'uid': 3，' name ':【T1]' Charlie ' }]
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向每个条目添加一个新字段
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```py
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for x in customers:
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x["password"]="123456" # any initial value
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print customers
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```
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输出:
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[{'password': '123456 '，' uid': 1，' name': 'John'}，{'password': '123456 '，' uid':
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2，' name': 'Smith'}，{'password': '123456 '，' uid': 3，' name': 'Andersson'}]
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删除字段
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```py
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del customers[1]
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print customers
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```
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Output:
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[{'uid': 1，' name': 'John'}，{'uid': 3，' name': 'Andersson'}]
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删除所有字段
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```py
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# This will delete id field of each entry.
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for x in customers:
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del x["id"]
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```
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Output:
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[{'name': 'John'}，{'name': 'Smith'}，{'name': 'Andersson'}]
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有关字典的更多信息，请参见这篇文章。 |