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[#]: subject: (Learn Python dictionary values with Jupyter)
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[#]: via: (https://opensource.com/article/21/3/dictionary-values-python)
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[#]: author: (Lauren Maffeo https://opensource.com/users/lmaffeo)
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[#]: collector: (lujun9972)
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[#]: translator: (DCOLIVERSUN)
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[#]: reviewer: ( )
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[#]: publisher: ( )
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[#]: url: ( )
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Learn Python dictionary values with Jupyter
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======
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Implementing data structures with dictionaries helps you access
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information more quickly.
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![Hands on a keyboard with a Python book ][1]
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Dictionaries are the Python programming language's way of implementing data structures. A Python dictionary consists of several key-value pairs; each pair maps the key to its associated value.
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For example, say you're a teacher who wants to match students' names to their grades. You could use a Python dictionary to map the keys (names) to their associated values (grades).
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If you need to find a specific student's grade on an exam, you can access it from your dictionary. This lookup shortcut should save you time over parsing an entire list to find the student's grade.
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This article shows you how to access dictionary values through each value's key. Before you begin the tutorial, make sure you have the [Anaconda package manager][2] and [Jupyter Notebook][3] installed on your machine.
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### 1\. Open a new notebook in Jupyter
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Begin by opening Jupyter and running it in a tab in your web browser. Then:
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1. Go to **File** in the top-left corner.
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2. Select **New Notebook**, then **Python 3**.
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![Create Jupyter notebook][4]
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(Lauren Maffeo, [CC BY-SA 4.0][5])
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Your new notebook starts off untitled, but you can rename it anything you'd like. I named mine **OpenSource.com Data Dictionary Tutorial**.
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The line number you see in your new Jupyter notebook is where you will write your code. (That is, your input.)
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On macOS, you'll hit **Shift** then **Return** to receive your output. Make sure to do this before creating new line numbers; otherwise, any additional code you write might not run.
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### 2\. Create a key-value pair
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Write the keys and values you wish to access in your dictionary. To start, you'll need to define what they are in the context of your dictionary:
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```
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empty_dictionary = {}
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grades = {
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"Kelsey": 87,
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"Finley": 92
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}
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one_line = {a: 1, b: 2}
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```
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![Code for defining key-value pairs in the dictionary][6]
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(Lauren Maffeo, [CC BY-SA 4.0][5])
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This allows the dictionary to associate specific keys with their respective values. Dictionaries store data by name, which allows faster lookup.
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### 3\. Access a dictionary value by its key
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Say you want to find a specific dictionary value; in this case, a specific student's grade. To start, hit **Insert** then **Insert Cell Below**.
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![Inserting a new cell in Jupyter][7]
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(Lauren Maffeo, [CC BY-SA 4.0][5])
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In your new cell, define the keys and values in your dictionary.
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Then, find the value you need by telling your dictionary to print that value's key. For example, look for a specific student's name—Kelsey:
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```
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# Access data in a dictionary
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grades = {
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"Kelsey": 87,
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"Finley": 92
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}
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print(grades["Kelsey"])
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87
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```
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![Code to look for a specific value][8]
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(Lauren Maffeo, [CC BY-SA 4.0][5])
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Once you've asked for Kelsey's grade (that is, the value you're trying to find), hit **Shift** (if you're on macOS), then **Return**.
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You see your desired value—Kelsey's grade—as an output below your cell.
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### 4\. Update an existing key
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What if you realize you added the wrong grade for a student to your dictionary? You can fix it by updating your dictionary to store an additional value.
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To start, choose which key you want to update. In this case, say you entered Finley's grade incorrectly. That is the key you'll update in this example.
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To update Finley's grade, insert a new cell below, then create a new key-value pair. Tell your cell to print the dictionary, then hit **Shift** and **Return**:
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```
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grades["Finley"] = 90
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print(grades)
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{'Kelsey': 87; "Finley": 90}
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```
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![Code for updating a key][9]
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(Lauren Maffeo, [CC BY-SA 4.0][5])
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The updated dictionary, with Finley's new grade, appears as your output.
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### 5\. Add a new key
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Say you get a new student's grade for an exam. You can add that student's name and grade to your dictionary by adding a new key-value pair.
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Insert a new cell below, then add the new student's name and grade as a key-value pair. Once you're done, tell your cell to print the dictionary, then hit **Shift** and **Return**:
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```
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grades["Alex"] = 88
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print(grades)
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{'Kelsey': 87, 'Finley': 90, 'Alex': 88}
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```
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![Add a new key][10]
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(Lauren Maffeo, [CC BY-SA 4.0][5])
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All key-value pairs should appear as output.
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### Using dictionaries
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Remember that keys and values can be any data type, but it's rare for them to be [non-primitive types][11]. Additionally, dictionaries don't store or structure their content in any specific order. If you need an ordered sequence of items, it's best to create a list in Python, not a dictionary.
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If you're thinking of using a dictionary, first confirm if your data is structured the right way, i.e., like a phone book. If not, then using a list, tuple, tree, or other data structure might be the best option.
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--------------------------------------------------------------------------------
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via: https://opensource.com/article/21/3/dictionary-values-python
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作者：[Lauren Maffeo][a]
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选题：[lujun9972][b]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://opensource.com/users/lmaffeo
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[b]: https://github.com/lujun9972
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[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/python-programming-code-keyboard.png?itok=fxiSpmnd (Hands on a keyboard with a Python book )
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[2]: https://docs.anaconda.com/anaconda/
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[3]: https://opensource.com/article/18/3/getting-started-jupyter-notebooks
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[4]: https://opensource.com/sites/default/files/uploads/new-jupyter-notebook.png (Create Jupyter notebook)
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[5]: https://creativecommons.org/licenses/by-sa/4.0/
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[6]: https://opensource.com/sites/default/files/uploads/define-keys-values.png (Code for defining key-value pairs in the dictionary)
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[7]: https://opensource.com/sites/default/files/uploads/jupyter_insertcell.png (Inserting a new cell in Jupyter)
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[8]: https://opensource.com/sites/default/files/uploads/lookforvalue.png (Code to look for a specific value)
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[9]: https://opensource.com/sites/default/files/uploads/jupyter_updatekey.png (Code for updating a key)
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[10]: https://opensource.com/sites/default/files/uploads/jupyter_addnewkey.png (Add a new key)
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[11]: https://www.datacamp.com/community/tutorials/data-structures-python
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@@ -0,0 +1,166 @@
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[#]: subject: (Learn Python dictionary values with Jupyter)
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[#]: via: (https://opensource.com/article/21/3/dictionary-values-python)
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[#]: author: (Lauren Maffeo https://opensource.com/users/lmaffeo)
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[#]: collector: (lujun9972)
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[#]: translator: (DCOLIVERSUN)
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[#]: reviewer: ( )
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[#]: publisher: ( )
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[#]: url: ( )
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用 Jupyter 学习 Python 字典
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======
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字典数据结构可以帮助你快速访问信息。
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![Python书与放在键盘上的手 ][1]
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字典是 Python 编程语言使用的数据结构。一个 Python 字典由多个键值对组成；每个对将键映射到其关联的值上。
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例如你是一名老师，想把学生姓名与成绩对应起来。你可以使用 Python 字典，将学生姓名映射到他们关联的成绩上。此时，键值对中键是姓名，值是对应的成绩。
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如果你想知道某个学生的考试成绩，你可以从字典中访问。这种快捷查询方式可以为你节省解析整个列表找到学生成绩的时间。
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本文介绍了如何通过键访问对应的字典值。学习前，请确保你已经安装了[Anaconda 包管理器][2]和 [Jupyter 笔记本][3]。
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### 1\. 在 Jupyter 中打开一个新的笔记本
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首先打开并在 Web 浏览器中运行 Jupyter。然后，
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1. 转到左上角的 **文件**。
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2. 选择 **新笔记本**，点击 **Python 3**。
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![新建 Jupyter 笔记本][4]
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(Lauren Maffeo, [CC BY-SA 4.0][5])
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开始时，新建的笔记本是无标题的，你可以将其重命名为任何名称。我为我的笔记本取名为 **OpenSource.com 数据字典教程**。
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笔记本中标有行号的位置就是你写代码的区域，也是你输入的位置。
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在 macOS 上，可以同时按 **Shift**、 **Return**键得到输出。在创建新的代码区域前，请确保完成上述行为；否则，你写的任何附加代码可能无法运行。
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### 2\. 新建一个键值对
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在字典中输入你希望访问的键与值。输入前，你需要在字典上下文中定义它们的含义：
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```
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empty_dictionary = {}
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grades = {
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"Kelsey": 87,
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"Finley": 92
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}
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one_line = {a: 1, b: 2}
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```
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![定义字典键值对的代码][6]
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(Lauren Maffeo, [CC BY-SA 4.0][5])
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这段代码让字典将特定键与其各自的值关联起来。字典按名称存储数据，从而可以更快地查询。
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### 3\. 通过键访问字典值
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现在你想查询指定的字典值；在上述例子中，字典值指特定学生的成绩。首先，点击 **Insert** 后选择 **Insert Cell Below**。
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![在 Jupyter 插入新建单元格][7]
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(Lauren Maffeo, [CC BY-SA 4.0][5])
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在新单元格中，定义字典中的键与值。
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然后，告诉字典打印该值的键，找到需要的值。例如，查询名为 Kelsey 的学生的成绩：
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```
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# 访问字典中的数据
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grades = {
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"Kelsey": 87,
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"Finley": 92
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}
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print(grades["Kelsey"])
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87
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```
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![查询特定值的代码][8]
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(Lauren Maffeo, [CC BY-SA 4.0][5])
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当你查询 Kelsey 的成绩（也就是你想要查询的值）时，如果你用的是 macOS，只需要同时按 **Shift**、 **Return** 键。
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你会在单元格下方看到 Kelsey 的成绩。
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### 4\. 更新已有的键
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当把一位学生的错误成绩添加到字典时，你会怎么办？可以通过更新字典、存储新值来修正这类错误。
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首先，选择你想更新的那个键。在上述例子中，假设你错误地输入了 Finley 的成绩，那么 Finley 就是你需要更新的键。
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为了更新 Finley 的成绩，你需要在下方插入新的单元格，然后创建一个新的键值对。同时按 **Shift**、 **Return** 键打印字典全部信息：
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```
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grades["Finley"] = 90
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print(grades)
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{'Kelsey': 87; "Finley": 90}
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```
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![更新键的代码][9]
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(Lauren Maffeo, [CC BY-SA 4.0][5])
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单元格下方输出带有 Finley 更新成绩的字典。
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### 5\. 添加新键
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假设你得到一位新学生的考试成绩。你可以用新键值对将那名学生的姓名与成绩补充到字典中。
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插入新的单元格，以键值对形式添加新学生的姓名与成绩。当你完成这些后，同时按 **Shift**、 **Return** 键打印字典全部信息：
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```
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grades["Alex"] = 88
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print(grades)
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{'Kelsey': 87, 'Finley': 90, 'Alex': 88}
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```
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![添加新键][10]
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(Lauren Maffeo, [CC BY-SA 4.0][5])
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所有的键值对输出在单元格下方。
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### 使用字典
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请记住，键与值可以是任意数据类型，但它们很少是[<ruby>扩展数据类型<rt>non-primitive types</rt>></ruby>>][11]。此外，字典不能以指定的顺序存储、组织里面的数据。如果你想要数据有序，最好使用 Python 列表，而非字典。
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如果你考虑使用字典，首先要确认你的数据结构是否是合适的，例如像电话簿的结构。如果不是，列表、元组、树或者其他数据结构可能是更好的选择。
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--------------------------------------------------------------------------------
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via: https://opensource.com/article/21/3/dictionary-values-python
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作者：[Lauren Maffeo][a]
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选题：[lujun9972][b]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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||||
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||||
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
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[a]: https://opensource.com/users/lmaffeo
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[b]: https://github.com/lujun9972
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[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/python-programming-code-keyboard.png?itok=fxiSpmnd (Hands on a keyboard with a Python book )
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[2]: https://docs.anaconda.com/anaconda/
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[3]: https://opensource.com/article/18/3/getting-started-jupyter-notebooks
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[4]: https://opensource.com/sites/default/files/uploads/new-jupyter-notebook.png (Create Jupyter notebook)
|
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[5]: https://creativecommons.org/licenses/by-sa/4.0/
|
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[6]: https://opensource.com/sites/default/files/uploads/define-keys-values.png (Code for defining key-value pairs in the dictionary)
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[7]: https://opensource.com/sites/default/files/uploads/jupyter_insertcell.png (Inserting a new cell in Jupyter)
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[8]: https://opensource.com/sites/default/files/uploads/lookforvalue.png (Code to look for a specific value)
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[9]: https://opensource.com/sites/default/files/uploads/jupyter_updatekey.png (Code for updating a key)
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[10]: https://opensource.com/sites/default/files/uploads/jupyter_addnewkey.png (Add a new key)
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[11]: https://www.datacamp.com/community/tutorials/data-structures-python
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