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Python-compatible regex for Markdown tables
My goal is to programatically convert Markdown tables to their HTML equivalents using regular expressions. I haven't been able to find any Python-compatible regexes for Markdown tables online, so I've been attempting to build my own. However, I've run into a bit of a snag. This is my code so far:
import re
# The text to be converted
markdown = """| Syntax | Description |
| ----------- | ----------- |
| Header | Title |
| Paragraph | Text |
"""
# Handles complex elements of the syntax
def assembleTable(match):
markdown = match.group(0)
# The problem line
html = re.sub(r'^\|(.*)\|\n(?:\| -{3,} )+\|$', r'<tr>\g<1></tr>', markdown, flags=re.MULTILINE)
return f'<table>\n{html}\n</table>'
# Basic table matching
html = re.sub(r'(?:^\|.*\|$\n?)+', assembleTable, markdown, flags=re.MULTILINE)
print(html)
It identifies a Markdown table and passes it into another function for processing, but the next step is where my trouble arises. The regex ^\|(.*)\|\n(?:\| -{3,} )+\|$ successfully matches a line of column headers, but I need to capture the individual headers' text so I can put them in <th></th> tags. I've been experimenting on regex101.com with (\| (.+?) )+ and ( .+? +?\|?), but the headers' variable number and whitespace is throwing me off and making it hard to integrate into the header regex.
How can I capture the individual column headers' text?
2 answers
You won't be able to do it for arbitrary length tables in a single regex matching the whole row. Capture groups are replaced when repeated. So any \| (?:(cell_text) \|)+ expression[1] will wind up with the capture group \g<1> as the last cell's text.
Instead, you'd have to send, say \|?[ \t]*(.*?)[ \t]s*\| to re.sub to replace each cell in a row with <td>\1</td> and wrap that in <tr></tr>.
-
Irrespective of whitespace ↩︎
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For an arbitrary number of rows and columns, a single regex won't work. You'll need to loop through all cells, replacing them as they are found. Something like this:
import re
markdown = """| Syntax | Description |
| ----------- | ----------- |
| Header | Title |
| Paragraph | Text |
"""
regex_cell = re.compile(r'\|([^|]+)')
cell = 'th'
previous = ' '
html = '<table>\n<tr>'
for match in regex_cell.finditer(markdown):
text = match[1].strip(' ')
if text == '\n':
# new row, unless it's the all-hyphens line or the end of string
if previous[0] != '-' and match.span()[1] != len(markdown):
html += '</tr>\n<tr>'
elif text[0] == '-': # header already rendered, change to td
cell = 'td'
else:
html += f'<{cell}>{text}</{cell}>'
previous = text
html += '</tr>\n</table>'
print(html)
I used [^|]+ to get the contents, which is "one or more characters that are not |". Then I remove the spaces, and check if it is a new line (which indicates a new tr), a hyphen (so I ignore the whole line) or a text (which becomes a td or th cell).
But honestly, regex is not the best tool for this job. You could search for specialized libraries that convert Markdown to HTML.
Or, if you want to keep it simple, just split the lines and cells:
markdown = """| Syntax | Description |
| ----------- | ----------- |
| Header | Title |
| Paragraph | Text |
"""
cell = 'th'
html = '<table>\n<tr>'
lines = markdown.split('\n')
for i, line in enumerate(lines):
# ignore line with hyphens, and change cell type from th to td
if '----' in line:
cell = 'td'
continue
for text in line.split('|'):
text = text.strip()
if text:
html += f'<{cell}>{text.strip()}</{cell}>'
if i < len(lines) - 2:
html += '</tr>\n<tr>'
html += '</tr>\n</table>'
print(html)
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