difflib adding an additional html column when making tables using difflib.HtmlDiff()
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type-bug
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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
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with the reproduction in diff_tool.py and the difflib.HtmlDiff().make_table entry point, using the supplied file_2 and file_2_new lists. Inspect how the generated rows and columns are assembled, then verify that the problematic input no longer produces an extra empty cell and add regression coverage for the reproduced case.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- tooling
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 42/100