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168 lines
6.6 KiB
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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: ( )
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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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