Text Templates in Python

Python provides built-in support for creating dynamic content or showing customized output to the user with the string.Template class. This class offers similar functionality to the text templates in other languages.

import sys
from string import Template

def main():
    # We can create a new template and parse its body from
    # a string.
    # Templates are a mix of static text and placeholders enclosed in
    # ${...} that are used to dynamically insert content.
    t1 = Template("Value is ${value}\n")

    # By "substituting" the template we generate its text with
    # specific values for its placeholders. The ${value} placeholder
    # is replaced by the value passed as a parameter to `substitute`.
    print(t1.substitute(value="some text"))
    print(t1.substitute(value=5))
    print(t1.substitute(value=["Python", "Java", "C++", "C#"]))

    # Helper function we'll use below.
    def create(template_string):
        return Template(template_string)

    # If the data is a dictionary we can use the ${key} placeholder to access
    # its values.
    t2 = create("Name: ${name}\n")

    print(t2.substitute({"name": "Jane Doe"}))

    # The same applies to objects; with objects we use the attribute names.
    class Person:
        def __init__(self, name):
            self.name = name

    print(t2.substitute(name=Person("Mickey Mouse").name))

    # Python's string.Template doesn't have built-in conditional logic,
    # but we can achieve similar results using string formatting or f-strings.
    def conditional_template(value):
        return "yes" if value else "no"

    print(f"{conditional_template('not empty')}\n")
    print(f"{conditional_template('')}\n")

    # For looping through lists, we can use list comprehension or join.
    t4 = create("Range: ${items}\n")
    items = ["Python", "Java", "C++", "C#"]
    print(t4.substitute(items=" ".join(items)))

if __name__ == "__main__":
    main()

This script demonstrates the following concepts:

Creating and using string templates with the string.Template class.
Substituting values into templates using dictionaries and named parameters.
Working with objects and their attributes in templates.
Implementing conditional logic (although not directly in the template syntax).
Handling lists and iteration.

When you run this script, you should see output similar to this:

Value is some text
Value is 5
Value is ['Python', 'Java', 'C++', 'C#']
Name: Jane Doe
Name: Mickey Mouse
yes
no
Range: Python Java C++ C#

Note that Python’s string.Template is simpler than some other template engines and doesn’t include built-in support for conditions or loops within the template syntax. For more complex templating needs, you might want to consider using a more feature-rich templating engine like Jinja2.

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Text Templates in Python