Build a template engine for reports

Creating a template engine for reports involves designing a system that takes structured data (like JSON or a database) and merges it with a template (with placeholders or tags) to generate formatted text (e.g., HTML, Markdown, PDF, or plain text reports).

Below is a basic but flexible template engine in Python. It supports:

• Placeholder replacement using {{ placeholder }}

• Conditional blocks

• Loops over data collections

🔧 Code: Template Engine in Python

python
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import re
from typing import Any, Dict

class ReportTemplateEngine:
    def __init__(self, template: str):
        self.template = template

    def render(self, context: Dict[str, Any]) -> str:
        rendered = self.template
        rendered = self._render_loops(rendered, context)
        rendered = self._render_conditionals(rendered, context)
        rendered = self._render_variables(rendered, context)
        return rendered

    def _render_variables(self, text: str, context: Dict[str, Any]) -> str:
        pattern = re.compile(r"{{s*(w+)s*}}")

        def replacer(match):
            key = match.group(1)
            return str(context.get(key, f'{{{{ {key} }}}}'))

        return pattern.sub(replacer, text)

    def _render_conditionals(self, text: str, context: Dict[str, Any]) -> str:
        pattern = re.compile(r"{% if (w+) %}(.*?){% endif %}", re.DOTALL)

        def replacer(match):
            key, content = match.group(1), match.group(2)
            return content if context.get(key) else ""

        return pattern.sub(replacer, text)

    def _render_loops(self, text: str, context: Dict[str, Any]) -> str:
        pattern = re.compile(r"{% for (w+) in (w+) %}(.*?){% endfor %}", re.DOTALL)

        def replacer(match):
            var_name, list_name, content = match.group(1), match.group(2), match.group(3)
            items = context.get(list_name, [])
            result = ""
            for item in items:
                result += self._render_variables(content, {**context, var_name: item})
            return result

        return pattern.sub(replacer, text)

📄 Example Template

text
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Report: {{ title }}

{% if author %}
Author: {{ author }}
{% endif %}

Sections:
{% for section in sections %}
- {{ section }}
{% endfor %}

🧪 Example Usage

python
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template = """
Report: {{ title }}

{% if author %}
Author: {{ author }}
{% endif %}

Sections:
{% for section in sections %}
- {{ section }}
{% endfor %}
"""

context = {
    "title": "Monthly Sales Report",
    "author": "Jane Doe",
    "sections": ["Overview", "Regional Breakdown", "Forecast"]
}

engine = ReportTemplateEngine(template)
output = engine.render(context)
print(output)

✅ Output

diff
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Report: Monthly Sales Report

Author: Jane Doe

Sections:
- Overview
- Regional Breakdown
- Forecast

🔄 Extendable Features

You can extend this engine with:

• Filters: {{ date | format_date }}

• Nested context: {{ user.name }}

• Custom functions or plugins

• Output to files (HTML, PDF with tools like weasyprint or pdfkit)

• Markdown rendering

Let me know if you want a web-based, CLI, or Django-style engine version.