Computer Science  ·  February 24, 2025

urllib.parse.urlencode()の使い方

前回に引き続き、urllib系のmoduleの話です。前回のurllib.request.urlopen()は、特定のURLを開いてその中身をojbectとして受け取り、そのあと、.read().decode("utf-8")により人間が読める形にして、HTMLとして出力したりするものでした。では、今回のurllib.parse.urlencode()は、いったい何をするものなのでしょうか。ChatGPTに聞いてみました。

 

１．使用例

 

まずは、使用例です。

Can you give me a simple example of "urllib.parse.urlencode()"?  

 

Sure! urllib.parse.urlencode() is used to encode a dictionary of parameters into a query string that can be appended to a URL.

Simple Example:

python
import urllib.parse
# Dictionary of parameters
params = { "search": "python urllib", "page": 1, "lang": "en" }
# Encode parameters into a query string
query_string = urllib.parse.urlencode(params)
# Example URL
base_url = "https://www.example.com/search?"
# Full URL with query string
full_url = base_url + query_string
print(full_url)

Output:

sql
https://www.example.com/search?search=python+urllib&page=1&lang=en

Explanation:

  • urllib.parse.urlencode(params) converts the dictionary into a properly formatted query string:
    ini
    search=python+urllib&page=1&lang=en
  • + replaces spaces by default.
  • The query string is appended to the base URL to form a valid HTTP request.

 

Let me know if you need more details! 🚀

 

この例では、Pythonのdictionaryをquery stringに変換し、それをBase URLの後ろに?を付けてから張り付けています。dictionaryは、

{ key:value, key:value, ...}

という形式をしていますが、これを

key=value&key=value&...

という形にするのがurllib.parse.urlencode()の機能のようです。また、spaceは

+

に変換されています。

 

２．?

 

上の例で、search?のあとに、key=valueが張り付けられていました。search?とは、何かを検索するためのcommandなのでしょうか。また、ChatGPTに聞いてみました。

 

I don’t know about "search?" in: https://www.example.com/search?

Is this some way of searching HTML?  

 

Good question! The ? in https://www.example.com/search? is not a way of searching HTML itself. Instead, it marks the beginning of the query string in a URL.

Explanation:

  1. Base URL:
    https://www.example.com/search

    • This is the main part of the URL, typically pointing to a web page or an API endpoint.

  2. Question Mark (?):

    • This separates the base URL from the query parameters.

  3. Query String (after ?):

    • Contains key-value pairs (name=value) that are passed to the web server.
    • Multiple parameters are separated by &.
    • Example:
      ini
      search=python+urllib&page=1&lang=en
    • This tells the server:
      • search=python urllib → The user is searching for "python urllib".
      • page=1 → Show the first page of results.
      • lang=en → Results should be in English.

Real-world Example:

If you search for "Python tutorial" on Google, you might see a URL like:

arduino
https://www.google.com/search?q=Python+tutorial
  • q=Python+tutorial means query=Python tutorial.

Key Takeaway:

  • ? starts the query string in a URL.
  • The query string sends information (like search terms or settings) to the server.
  • Many websites and APIs use this method to process user requests.

Would you like to try making your own query string? 😊

 

このように、予想外の答えが返ってきました。?は、検索とか質問とかの意味はなく、query stringの始まりを示すための記号でした。例で、URLがsearchで終わっているのは、たまたまそうなっていただけで、とにかく、Base URLの後ろに?をくっつけると、そのあと、query stringをURLに張り付けてserverに送ることができるのでした。

 

これは、PHPのGET methodと同じようなので、それもChatGPTに聞いてみました。

 

３．GET methodとの比較

 

So the browser is sending information after "?", isn't it?  It is like PHP's GET method?

 

Yes, exactly! The browser sends information after the ? in the URL, just like PHP's GET method.

How It Works:

  • The browser makes an HTTP request to the server.
  • The query string (everything after ?) contains key-value pairs.
  • The server reads these values and processes them, just like handling $_GET in PHP.

PHP Example:

If a user visits this URL:

arduino
https://www.example.com/search?keyword=python&page=2

In PHP, you can access the values like this:

php
<?php echo $_GET["keyword"]; // Output: python echo $_GET["page"]; // Output: 2 ?>

So yes, it's just like using the GET method in PHP!

 

Would you like an example of how to construct a URL with query parameters in Python? 😊

 

このように、URLにデータをくっつけてserverに送るのは、GET methodと同じだという返答でした。

 

 

４．how to construct a URL with query parameters in Python

 

ChatGPTがそのメッセージの最後のところで、construct a URLの例を作りましょうかと言ってきたので、Yesと言って、例を作らせました。

 

Yes, and also, tell me what does it mean by constructing a URL with query parameters.

 

What Does "Constructing a URL with Query Parameters" Mean?

It means building a URL that includes data in the query string (after ?), so that the server can understand what the user is requesting.

For example, if you search for "Python" on a website, the browser might generate a URL like:

arduino
https://www.example.com/search?keyword=Python&page=1

Here:

  • ?keyword=Python → Tells the server you searched for "Python."
  • &page=1 → Tells the server you want page 1 of the results.

This is similar to PHP’s $_GET, where the server reads the values after ?.

Example in Python Using urllib.parse.urlencode()

Let’s say we want to search for "Python" on "www.example.com/search" and request "page 1".
We can construct the URL like this:

python
import urllib.parse
# Define query parameters as a dictionary
params = { "keyword": "Python", "page": 1 }
# Encode the parameters into a query string
query_string = urllib.parse.urlencode(params)
# Construct the full URL
url = "https://www.example.com/search?" + query_string
print(url)

Output:

arduino
https://www.example.com/search?keyword=Python&page=1

The function urllib.parse.urlencode(params) converts the dictionary into a proper query string.

Why Use urlencode()?

  1. Automatically formats special characters
    • If your keyword is "C++", it correctly encodes it as C%2B%2B.
  2. Handles multiple parameters easily
    • Instead of manually writing ?keyword=Python&page=1, urlencode() does it for you.
  3. Avoids mistakes with & and =
    • Ensures correct structure when combining multiple parameters.

Would you like an example where we send this URL in a request? 🚀

 

さらに、serverに送る例を作るというので、それもYesと答えました。

 

５．an example where we send this URL in a request

 

Yes, please.

 

Here's a complete example where we construct a URL with query parameters and send a request using urllib.request.urlopen().

📝 Example: Send a Request with Query Parameters

python
import urllib.parse
import urllib.request
# Define base URL and query parameters
base_url = "https://www.example.com/search"
params = { "keyword": "Python programming", "page": 1 }
# Encode the parameters into a query string
query_string = urllib.parse.urlencode(params)
# Construct the full URL
full_url = base_url + "?" + query_string
print("Requesting URL:", full_url)
# Send GET request
response = urllib.request.urlopen(full_url)
# Read and decode response content
content = response.read().decode("utf-8")
# Print first 500 characters of response (for readability)
print(content[:500])

🔍 What This Code Does:

  1. Creates a base URL (https://www.example.com/search).
  2. Defines query parameters (keyword=Python programming and page=1).
  3. Encodes the parameters into a proper query string (keyword=Python+programming&page=1).
  4. Appends the query string to the base URL to form the full request URL.
  5. Sends an HTTP request to the constructed URL.
  6. Reads and decodes the server's response.

🔥 Example of Final URL Generated:

arduino
https://www.example.com/search?keyword=Python+programming&page=1

This is exactly like typing a search query in a browser! 🌍

🛑 Important Notes:

  • If running this code, use a real website like "https://httpbin.org/get" (which echoes requests).
  • Some websites block urllib requests (consider using requests library instead).
  • If you get an SSL error, try:
    python
    import ssl
    context = ssl._create_unverified_context()
    response = urllib.request.urlopen(full_url, context=context)

Would you like an example with the requests library, which is more user-friendly? 🚀

 

これは、urllib.parse.urlencode()でquery stringを作成して、それをbase URLに?をつけてはりつけたものを、urllib.request.urlopen()でserverに送って、そのresponseを.read()と.decode("utf-8")でHTMLとして読める状態にする、というものでした。