python / python/cpython

difflib adding an additional html column when making tables using difflib.HtmlDiff()

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Python
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Description

Bug report

Bug description:

I am working with the python library difflib and specifically the class HtmlDiff. For some reason, the function make_table is adding a blank column in when generating an HTML table, throwing off difference highlights and defeating the entire purpose of the diff function alltogether.

Input python function:

# diff_tool.py

import argparse
import difflib
import sys

from pathlib import Path


def create_diff(output_file: Path = None):
        
    # short list of strings to compare, nonproblematic (see expected output)
    thing1 = ["this", "that"]
    thing2 = ["thiis", "that2"]

    # longer list of strings to compare, mirroring the problematic data (see actual output)
    file_2 = ['Ab', 
    'my_id: ID1234, attribute: abcd fghijklmn py stuvwx zabc efg ijklmnopy st vwxy abcd f , name: abcd fghijklmn py stuvwx zabc efg ijklmnopy st vwxy abcd f ', 
    'my_id: ID5678, attribute: abcde ghijklm opyrst vwxyz bc efghij lmnopyr tuv xyzab defabcde ghijklmno yrstuvwxyza cdefghijklmnop rstuvw yz b defab defgh jklmnop rstuvwxyz bcd fghijkl nopyr tuvwxyza cdefabcd fghijkl no yrs uvwxyzabcd fghij l n, name: ab defghi klmnopy stuvwxy abcde ghijklm op']
                   
    file_2_new = ['Abcdefghijklmn', 
    'my_id: ID1234, attribute: abcde ghijklm opyrst vwxyz bc efghij lmnopyr tuv xyzab defabcde ghijklmno yrstuvwxyza cdefghijklmnop rstuvw yz b defab defgh jklmnop rstuvwxyz bcd fghijkl nopyr tuvwxyza cdefabcd fghijkl no yrs uvwxyzabcd fghij l n, name: ab defghi klmnopy stuvwxy abcde ghijklm op', 
    'my_id: ID5678, attribute: abcd fghijklmn py stuvwx zabc efg ijklmnopy st vwxy abcd f , name: abcd fghijklmn py stuvwx zabc efg ijklmnopy st vwxy abcd f ']

    # if output HTML file option at command line
    if output_file:
    
        # create HtmlDiff Object
        my_html = difflib.HtmlDiff()
        
        # make table with problematic data, delta1 is a string
        delta1 = my_html.make_table(
            file_2, file_2_new, "table1A" , "table1B"
        )     

        # replace nowrap tags and weird space characters
        delta1 = delta1.replace(" ", " ")
        delta1 = delta1.replace("nowrap=\"nowrap\"", "")

        # html header which goes at beggining of html file
        html_header = '''

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
          "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html>
<body style="background-color:white;">
<head>
    <meta http-equiv="Content-Type"
          content="text/html; charset=utf-8" />
    <title></title>
    <style type="text/css">
        table.diff {font-family:Courier; color: black; border:medium;table-layout: auto; width: 96%; word-wrap: break-word; margin-left: auto; margin-right: auto;}
        td.diff_header {text-align:left}
        .diff_header {background-color:#e0e0e0}
        .diff_next {background-color:#c0c0c0}
        .diff_add {background-color:#aaffaa}
        .diff_chg {background-color:#ffff77}
        .diff_sub {background-color:#ffaaaa}
        .widthA{width:1%}
        .widthB{width:7%}
        .widthC{width:40%}
        .element_title{color: black; text-align:center}
        .element_diff{color: black; width: 96%; margin-left: auto; margin-right: auto}
    </style>
</head>

'''
        # html footer which goes at the end of html file
        html_footer = '''
        </body>

</html>
        '''
        
        # open output file path and write header, table and footer
        with open(output_file, "w") as f:
            f.write(html_header)
            f.write(delta1)
            f.write(html_footer)
    

def main():

    # parse command line option for output HTML file
    parser = argparse.ArgumentParser()
    parser.add_argument("--html", help="specify html to write to")
    args = parser.parse_args()


    if args.html:
        output_file = Path(args.html)
    else:
        output_file = None

    # call create_diff function which compares two lists of strings
    # and returns a formatted HTML table comparing them
    create_diff(output_file)


if __name__ == "__main__":
    main()

Output HTML file with problematic data:



<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
          "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html>
<body style="background-color:white;">
<head>
    <meta http-equiv="Content-Type"
          content="text/html; charset=utf-8" />
    <title></title>
    <style type="text/css">
        table.diff {font-family:Courier; color: black; border:medium;table-layout: auto; width: 96%; word-wrap: break-word; margin-left: auto; margin-right: auto;}
        td.diff_header {text-align:left}
        .diff_header {background-color:#e0e0e0}
        .diff_next {background-color:#c0c0c0}
        .diff_add {background-color:#aaffaa}
        .diff_chg {background-color:#ffff77}
        .diff_sub {background-color:#ffaaaa}
        .widthA{width:1%}
        .widthB{width:7%}
        .widthC{width:40%}
        .element_title{color: black; text-align:center}
        .element_diff{color: black; width: 96%; margin-left: auto; margin-right: auto}
    </style>
</head>


    <table class="diff" id="difflib_chg_to0__top"
           cellspacing="0" cellpadding="0" rules="groups" >
        <colgroup></colgroup> <colgroup></colgroup> <colgroup></colgroup>
        <colgroup></colgroup> <colgroup></colgroup> <colgroup></colgroup>
        <thead><tr><th class="diff_next"><br /></th><th colspan="2" class="diff_header">table1A</th><th class="diff_next"><br /></th><th colspan="2" class="diff_header">table1B</th></tr></thead>
        <tbody>
            <tr><td class="diff_next" id="difflib_chg_to0__0"><a href="#difflib_chg_to0__top">t</a></td><td class="diff_header" id="from0_1">1</td><td ><span class="diff_sub">Ab</span></td><td class="diff_next"><a href="#difflib_chg_to0__top">t</a></td><td class="diff_header" id="to0_1">1</td><td ><span class="diff_add">Abcdefghijklmn</span></td></tr>
            <tr><td class="diff_next"></td><td class="diff_header" id="from0_2">2</td><td ><span class="diff_sub">my_id: ID1234, attribute: abcd fghijklmn py stuvwx zabc efg ijklmnopy st vwxy abcd f , name: abcd fghijklmn py stuvwx zabc efg ijklmnopy st vwxy abcd f </span></td><td class="diff_next"></td><td class="diff_header"></td><td ></td></tr>
            <tr><td class="diff_next"></td><td class="diff_header" id="from0_3">3</td><td >my_id: ID<span class="diff_chg">5678</span>, attribute: abcde ghijklm opyrst vwxyz bc efghij lmnopyr tuv xyzab defabcde ghijklmno yrstuvwxyza cdefghijklmnop rstuvw yz b defab defgh jklmnop rstuvwxyz bcd fghijkl nopyr tuvwxyza cdefabcd fghijkl no yrs uvwxyzabcd fghij l n, name: ab defghi klmnopy stuvwxy abcde ghijklm op</td><td class="diff_next"></td><td class="diff_header" id="to0_2">2</td><td >my_id: ID<span class="diff_chg">1234</span>, attribute: abcde ghijklm opyrst vwxyz bc efghij lmnopyr tuv xyzab defabcde ghijklmno yrstuvwxyza cdefghijklmnop rstuvw yz b defab defgh jklmnop rstuvwxyz bcd fghijkl nopyr tuvwxyza cdefabcd fghijkl no yrs uvwxyzabcd fghij l n, name: ab defghi klmnopy stuvwxy abcde ghijklm op</td></tr>
            <tr><td class="diff_next"></td><td class="diff_header"></td><td ></td><td class="diff_next"></td><td class="diff_header" id="to0_3">3</td><td ><span class="diff_add">my_id: ID5678, attribute: abcd fghijklmn py stuvwx zabc efg ijklmnopy st vwxy abcd f , name: abcd fghijklmn py stuvwx zabc efg ijklmnopy st vwxy abcd f </span></td></tr>
        </tbody>
    </table>
        </body>

</html>

The problematic line in the HTML is:

<tr><td class="diff_next"></td><td class="diff_header" id="from0_2">2</td><td ><span class="diff_sub">my_id: ID1234, attribute: abcd fghijklmn py stuvwx zabc efg ijklmnopy st vwxy abcd f , name: abcd fghijklmn py stuvwx zabc efg ijklmnopy st vwxy abcd f </span></td><td class="diff_next"></td><td class="diff_header"></td><td ></td></tr>

Where there is an extra <td ></td> at the end, adding an extra column.

This is what the table looks like with the unwanted column

This is what the table is supposed to look like when the columns are aligned correctly

I have tried changing the length of the string, checking for invisible characters, removing colons. There is something wrong with the strings that I am providing as input which throws off the make_table function. I have provided make_table with longer strings and the output was just fine. The behavior is very inconsistent.

Thanks for the help.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

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  4. Ouvrez une pull request qui référence le numéro de l'issue.

Piste de recherche

Commencez par la reproduction dans diff_tool.py et le point d’entrée difflib.HtmlDiff().make_table, en utilisant les listes file_2 et file_2_new fournies. Examinez comment les lignes et les colonnes générées sont assemblées, puis vérifiez que l’entrée problématique ne produit plus de cellule vide supplémentaire et ajoutez une couverture de régression pour le cas reproduit.

Rédigé par le modèle d'indexation à partir du texte de l'issue.

Évaluation

Stack technique
python
Domaine
tooling
Type d'issue
Bug
Difficulté
3/5
Temps estimé
1-2 jours
Activité
À l'abandon
Clarté
Plutôt claire
Accessibilité débutants
42/100

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