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  • JSON. JavaScript Object Notation. It's a small, lightweight, data format. A packet

  • of JSON data is almost identical to a Python dictionary. It is shorter than XML,

  • and can be quickly parsed by browsers since it uses JavaScript syntax. This makes

  • JSON an ideal format for transporting data between a client and a server. If

  • your client is not a browser, don't worry. Android and other mobile operating

  • systems all come equipped with tools for parsing and working with JSON. Today, I

  • will show you how to use Python's JSON library to send and receive JSON data

  • packets. We'll have a ton of fun with JSON sent from my Rayguns. Pew Pew!

  • Here is a typical JSON data packet. Notice how it looks just like a Python dictionary with

  • a few exceptions. True and false are not capitalized in JSON, while in Python

  • they are. And instead of none you use JavaScript value null. This JSON object

  • contains examples of all possible data types. All the keys are strings, but the

  • values can be strings, numbers, booleans, a list, null, or even another JSON object. Now

  • compare this with the XML version. The increased size of XML data is largely

  • due to the end tags repeating the text of the opening tags. A popular sport is

  • debating the merits of JSON versus XML. But instead of arguing, I recommend you

  • learn the pros and cons of both formats, then choose the one which is best for your project.

  • Let's now learn how to use the JSON module in Python.

  • First, let's save the sample JSON data to a txt file.

  • Notice the Cinematographer's name

  • contains a non ASCII character. For this reason, we will save this text file using

  • utf-8 encoding. Begin by importing the JSON module. Next, let's look at the

  • methods in this module. Today, we will focus on the load and dump methods.

  • The load method allows you to load JSON data from a file, while the load s method

  • enables you to load JSON data from a string. That's why there's an S at the

  • end of the method name: s for string. The dump method will

  • write JSON data to a file, and the dump s method will output a string in proper

  • JSON format. Let's see some examples. First, we will load the JSON data from

  • the file we created earlier. Using the open function, the first argument is the

  • path to the file. For the second argument, let's pass R, since we are only reading

  • the data. Next, specify the encoding is utf-8, since this data contains non ASCII

  • characters. Now that we have opened the file, we can load the JSON data using the

  • load method. After loading the JSON data, close the file. If you display the object,

  • you will see a dictionary containing all the data. If you look at the type, you

  • will see it is, in fact, a dictionary. Also notice how the true/false and null

  • values from the file were correctly parsed into Python true/false and none

  • values. And the non ASCII character was correctly parsed. If you look up the 142

  • Unicode character, it is a lowercase L with the stroke. Because this is a

  • dictionary, you can access the data by key. We can see the title, the list of

  • actors, and so on.

  • You use the load s function if your JSON data arrives in

  • the form of a string. This is common in client-server applications where data is

  • sent over the net. As an illustration, let's create a string with a JSON

  • formatted value. To parse this JSON data, call the load s function. Since all

  • characters are ASCII, there is no need to worry about encoding. If you look at the

  • result, we have a valid Python dictionary with all data properly converted. False

  • is the Python boolean and null was converted to none.

  • Suppose you want to store the data about Gattaca in a database, or send it to a remote user.

  • To convert this dictionary into a valid JSON string you use the dump s method

  • When you call the method simply pass in the dictionary. The result is a string in

  • proper JSON format. Notice that true and false are both lowercase, and none was

  • converted to null. There is an unusual double stroke for the non ASCII

  • character, however. This is because the JSON library assumes you want the output

  • to be ASCII, and will escape all non-ASCII

  • characters. To avoid this, and allow Unicode characters in your string, call

  • dump s, and set ensure ASCII to false. The non ASCII character is now preserved and

  • the backslash is not escaped.

  • Let's now create a new object, convert it to JSON,

  • and write it to a file. we start by creating a dictionary. For this example,

  • we will use data for the movie Minority Report. Directed by Steven Spielberg, with

  • a soundtrack by John Williams... this is a must-see movie for any Python programmer.

  • The cinematographer is Janusz Kaminsky. The N in his last name has an accent

  • with a Unicode values of 144. To write this to a file in JSON format, we must

  • first open a file in write mode with utf-8 encoding. Next call the dump

  • method. The first argument is the dictionary. Now pass in the file.

  • Remember to set ensure ASCII to false, since our data contains non ASCII characters.

  • Finally, close the file. If we open the file, we see all the data is there.

  • Everything is properly formatted, and the Unicode characters are all accounted for

  • Please wait for an incoming message from Socratica...

  • This JSON says Patreon helps Python to carry on...

  • and since rhyming sentences are twice as likely to be true

  • as ordinary ones, this message must be as good as gold...

  • which is what we are asking for, if you have some to spare.

JSON. JavaScript Object Notation. It's a small, lightweight, data format. A packet

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JSON在Python中的應用 ||Python教程 ||學習Python編程 (JSON in Python || Python Tutorial || Learn Python Programming)

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    林宜悉 發佈於 2021 年 01 月 14 日
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