Introducing t-strings in Python 3.14: A Safer, Flexible Alternative to f-strings

After the popularity of f-strings introduced in Python 3.6, their misuse can lead to security problems such as SQL injection and XSS; Python 3.14 will add t-strings (template strings) as a safer, more flexible alternative, expected in late 2025.

What are t-strings? t-strings are a generalized form of f-strings that create a string.templatelib.Template object instead of an immediate string. The Template type lacks a __str__() method, so developers must process the object (e.g., via an html() function) before rendering, allowing safe escaping of dynamic content.

Example of building a safe HTML element:

<code>from string.templatelib import Template

evil = "<script>alert('bad')</script>"

template = t"<p>{evil}</p>"

safe_html = html(template)  # Returns escaped HTML, preventing XSS</code>

Flexibility of t-strings extends beyond security; they support complex interpolations such as attribute dictionaries:

<code>attributes = {"src": "roquefort.jpg", "alt": "Yum"}

template = t"<img {attributes} />"

element = html(template)  # Produces a complete <img> tag</code>

For developers familiar with JavaScript, t-strings resemble tag templates, offering a comparable way to embed expressions within markup.

How to use t-strings? The Template object provides .strings and .values tuples, can be iterated, and exposes detailed interpolation metadata ( .interpolations with value , expression , conversion , format_spec ).

<code>name = "World"
template = t"Hello {name}!"
print(template.strings)   # ('Hello ', '!')
print(template.values)    # ('World',)

for item in template:
    print(item)
</code>

Templates can also be instantiated directly:

<code>from string.templatelib import Template, Interpolation

template = Template("Hello ", Interpolation(value="World", expression="name"), "!")</code>

Sample application – converting template content to pig Latin demonstrates the power of processing each interpolation:

<code>def pig_latin(template: Template) -> str:
    """Convert a Template to pig Latin"""
    result = []
    for item in template:
        if isinstance(item, str):
            result.append(item)
        else:
            word = item.value
            if word and word[0] in "aeiou":
                result.append(word + "yay")
            else:
                result.append(word[1:] + word[0] + "ay")
    return "".join(result)

name = "world"
template = t"Hello {name}!"
print(pig_latin(template))  # Output: Hello orldway!</code>

The article concludes with a forward‑looking view: t-strings are expected to become widely adopted in libraries and frameworks, especially for handling user input, and tooling such as black , ruff , and VS Code should evolve to support them. The feature is driven by PEP 750 contributors including Dave Peck, Jim, Paul, Koudai, Lysandros, and Guido.