The main difference between string.Template from Python's string module and jinja2.Template from the Jinja2 templating engine lies in their syntax and features.

Step 1: Creating the Template

string.Template:

from string import Template

temp = Template("Today is $today and tomorrow is $tomorrow.")

• Syntax: In string.Template, placeholders are denoted by a dollar sign ($), followed by the variable name (e.g., $today, $tomorrow).

jinja2.Template:

from jinja2 import Template

temp = Template("Today is {{today}} and tomorrow is {{tomorrow}}.")

• Syntax: In Jinja2, placeholders are denoted by double curly braces ({{}}), surrounding the variable name (e.g., {{today}}, {{tomorrow}}).

Step 2: Rendering the Template

string.Template:

out = temp.substitute(today="Monday")
print(out)

• Rendering Method: The substitute() method replaces the placeholders with the provided values.
• Error Handling: If a value for a placeholder is not provided, it raises a KeyError.

If you want to avoid an error when a variable is missing, you can use safe_substitute():

out = temp.safe_substitute(today="Monday")
print(out)

• safe_substitute(): This method substitutes provided values and leaves placeholders for missing ones, instead of raising an error.

jinja2.Template:

out = temp.render(today="Monday")
print(out)

• Rendering Method: Jinja2 uses the render() method to replace placeholders with provided values.
• Error Handling: If a variable is missing in Jinja2, it does not throw an error. Instead, it leaves the placeholder empty (i.e., it renders nothing for that variable).

Summary of Differences:

1. Syntax:

   • string.Template: $variable
   • jinja2.Template: {{variable}}

2. Rendering:

   • string.Template: Uses substitute() or safe_substitute().
   • jinja2.Template: Uses render().

3. Error Handling:

   • string.Template:
     • substitute(): Throws a KeyError if any placeholder is missing.
     • safe_substitute(): Leaves missing variables unchanged, without raising an error.
   • jinja2.Template: Leaves missing variables empty (blank) without throwing an error.