[Python] How to render a Jinja2 template field with correct capitalisation depending on field...

I am trying to render an HTML field with the same string, in this example it's "pots and pans". I need to ensure that if the {{ example_field }} is at the beginning of sentence it is capitalised and if not it's lowercase.

I've tried numerous iterations on the following and this is where I got to which does not work.

from jinja2 import Environment, PackageLoader, select_autoescape

environment = Environment()

EXAMPLE_BODY_1 = """
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Example</title>
</head>
<body>
<div><h2>Example Contract Term</h2></div>
<div>
<p>
Sometimes the example_field is in the middle so needs to be lowercase,
{{ example_field }} is a good example.
</p>
<ul>
<i>All terms in this example are binding.</i>
<i>The terms are made up as this is an example.</i>
<i>Terms can always change.</i>
</ul>
</div>

<div><h2>Example Contract Other Term</h2></div>
<div>
<p>
{{ example_field }} can also be at the start of a sentence to therefore
needs to be capitalised.
</p>
<ul>
<i>Sometimes it's like the first example.</i>
<i>The terms are made up as this is an example.</i>
<i>Terms can always change.</i>
</ul>
</div>
</body>
</html>
"""

def capitalize_if_start_of_html_sentence(value, html_content):
# Normalize whitespace and remove HTML tags
content = ' '.join(html_content.split())

# Split the content into sentences using common sentence-ending punctuation
sentences = content.split('. ')

for sentence in sentences:
# Further split by other sentence-ending punctuation
sub_sentences = sentence.split('? ')
for sub_sentence in sub_sentences:
sub_sub_sentences = sub_sentence.split('! ')
for sub_sub_sentence in sub_sub_sentences:
# Check if the sub-sentence starts with the example_field placeholder
if sub_sub_sentence.startswith('{{ example_field }}'):
return value.capitalize()
return value.lower()

# Add the custom filter to the environment
environment.filters['capitalize_if_start_of_html_sentence'] = lambda value: capitalize_if_start_of_html_sentence(value, EXAMPLE_BODY_1)

# Create a template from string
template = environment.from_string(EXAMPLE_BODY_1)

example_merge_field = "pots and pans"

# Render the template with the custom filter applied
print(template.render(example_field=example_merge_field))

# Apply the filter manually to the example_field
capitalized_example_field = capitalize_if_start_of_html_sentence(example_merge_field, EXAMPLE_BODY_1)

# Render the template with the manually capitalized field
print(template.render(example_field=capitalized_example_field))


I also tried using HTMLParser as the data contents do have the correct {{ example_field }} then the text extracted which I could do starts with but I can't work it out.

from html.parser import HTMLParser

class MyHTMLParser(HTMLParser):
def handle_starttag(self, tag, attrs):
print("Encountered a start tag:", tag)

def handle_data(self, data):
print("Data :", data)


This is what I am trying to achieve:

# Expected output
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Example</title>
</head>
<body>
<div><h2>Example Contract Term</h2></div>
<div>
<p>
Sometimes the example_field is in the middle so needs to be lowercase,
pots and pans is a good example.
</p>
<ul>
<i>All terms in this example are binding.</i>
<i>The terms are made up as this is an example.</i>
<i>Terms can always change.</i>
</ul>
</div>

<div><h2>Example Contract Other Term</h2></div>
<div>
<p>Pots and pans can also be at the start of a sentence to therefore
needs to be capitalised.
</p>
<ul>
<i>Sometimes it's like the first example.</i>
<i>The terms are made up as this is an example.</i>
<i>Terms can always change.</i>
</ul>
</div>
</body>
</html>

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