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UnicodeDecodeError: ‘cp932’ codec can’t decode byte 0x99 in position ~ : illegal multibyte sequence

2020-06-14 Python TroubleShooting

Problem

When I open the file in Python, the error “UnicodeDecodeError: ‘cp932’ codec can’t decode byte 0x99 in position ~ : illegal multibyte sequence” occurred.

The code is as below.

path = 'wordpress/wp-admin/about.php'

with open(path) as f:
            lines = f.readlines()
            print(lines)

Environment

Windows 10
Python 3.8.6

The cause of this problem

The character code ‘cp932’ is Microsoft Cade page 932(Shift_JIS). And ‘0x99’ is the number of 1byte represented by hexadecimal. This error occurs when the character code used for decoding the file does not match the character code of the file.

Solution

Solution 1. Use encoding option argument

If you know the coding of the file, you can specify it with option argument of open() function.

with open(path, encoding = "utf_8") as f:
    lines = f.readlines()
    print(lines)

Solution 2. Use try and except

If you’d like to use a few character coding and ignore files of other character coding.

try:
    with open(path, encoding = "shift_jis") as f:
        lines = f.readlines()
        print(lines)
except:
    pass
try:
    with open(path, encoding = "ascii") as f:
        lines = f.readlines()
        print(lines)
except:
    pass
try:
    with open(path, encoding = "utf_8") as f:
        lines = f.readlines()
        print(lines)
except:
    pass

Solution 3. Use chardet

Chardet is a module to detect the character encoding.

Install chardet with pip command.

> pip install chardet

Installing collected packages: chardet
....
Successfully installed chardet-3.0.4

You can get the character encoding by chardet.dect(<binary data>).

import chardet
path = 'wordpress/wp-admin/about.php'

with open(path, mode='rb') as f:
    binary = f.read()
    code = chardet.detect(binary)['encoding']
with open(path, encoding=code) as f:
    lines = f.readlines()
    print(lines)

Solution 4. Ignore errors by codec

You can ignore errors by using codec.open() and setting the option argument ‘errors’ ‘ignore’.

import codec
path = 'wordpress/wp-admin/about.php'

with codecs.open(path, 'r', 'utf-8', 'ignore') as f:
    lines = f.readlines()
    print(lines)

Why does category list return “Uncategorized”?

2020-06-12 PHP TroubleShooting WordPress

Problem

I’d like to display the list of all categories in my theme, but it return “Uncategorized”. The PHP code in index,php is as below.

<h1>Categories</h1>
<?php
	$categories = get_the_category();
	if ( $categories ) {
		foreach( $categories as $category ) {
			$output .= '<a href="' . get_category_link($category->term_id) 
			. '">' . $category->cat_name . '</a>' . ' ';
		}
		echo $output;
	}
?>

The result is the following.

The cause of this problem

get_the_category(); is the function to get the categories of “current” post or page. This page is index.php with no category, so it return “Uncategorized”.

Solution

Use get_categories(); instead of get_the_category();.

<h1>Categories</h1>
<?php
	$categories = get_categories();
	if ( $categories ) {
		foreach( $categories as $category ) {
			$output .= '<a href="' . get_category_link($category->term_id) 
				. '">' . $category->cat_name . '</a>' . ' ';
		}
	echo $output;
	}
?>

This is the result.

How to change loop times in WordPress

2020-06-10 PHP WordPress

GOAL

To stop the loop at the number of times specified in WordPress.

Environment

WordPress 5.5.1

Loop in WordPress

The Loop is PHP code used by WordPress to display posts. The following is an example of the loop.

<?php 
if ( have_posts() ) {
	while ( have_posts() ) {
		the_post(); 
		//
		// Post Content here
		//
	} // end while
} // end if
?>

Check “The Loop” in wordpress.org for details about the loop.

Method

Use get_posts function

<?php
	$recentposts = get_posts( array( 'posts_per_page' => 3) );
	if ( $lastposts ) {
    		foreach ( $lastposts as $post ) : setup_postdata( $post );
			the_title();
        		//
			// Post Content here
			//
		endforeach; 
    		wp_reset_postdata();
	} //end if
?>

Appendix

Though <?php query_posts(‘posts_per_page=NUMBER’); ?> can be also used to limit the number of posts, it is not recommended.