Template method from Python’s string module provides a safe, simple, and readable way to perform string substitution using $identifier placeholders in a template string, with values supplied from a dictionary or mapping. Unlike f-strings or .format(), it strictly separates the template from the data, making it ideal for user-provided templates, configuration files, internationalization, or cases where you want to prevent code injection or accidental expression evaluation. In 2026, string.Template remains useful — especially for secure templating, legacy code migration, or when you need basic substitution without the full power (and risk) of f-strings or format specifiers. It’s slower than f-strings but safer and more predictable for certain use cases.
Here’s a complete, practical guide to the Template method in Python: basic usage, safe substitution, advanced features, real-world patterns, comparison with f-strings/.format(), and modern best practices with type hints, safety, and pandas/Polars integration.
Create a Template object with placeholders in $var or ${var} form — then use .substitute() or .safe_substitute() with a mapping.
from string import Template
# Basic template with $name placeholder
tmpl = Template("Hello, $name! Welcome to $place.")
message = tmpl.substitute(name="Alice", place="Python World")
print(message)
# Hello, Alice! Welcome to Python World.
Use .safe_substitute() to avoid KeyError — missing keys are left as-is (useful for partial templates).
partial = Template("Hello, $name! Your score is $score.")
print(partial.safe_substitute(name="Bob"))
# Hello, Bob! Your score is $score. (no error, $score unchanged)
# Raises KeyError with .substitute()
# partial.substitute(name="Bob") # ? KeyError: 'score'
Advanced placeholders — ${var} for disambiguation, $$ for literal dollar sign.
price_tmpl = Template("Item: ${item}, Price: $$${price}")
print(price_tmpl.substitute(item="Coffee", price=4.50))
# Item: Coffee, Price: $4.50
complex_tmpl = Template("User ${user_id} ($${username}) logged in.")
print(complex_tmpl.substitute(user_id=123, username="alice"))
# User 123 ($alice) logged in.
Real-world pattern: secure user-provided templates — Template prevents code execution, unlike f-strings or .format() with untrusted input.
# Safe email template from user config
email_template = Template(user_config["greeting_template"])
email_body = email_template.safe_substitute(
username="alice",
login_date="2026-02-10",
support_link="https://example.com/support"
)
print(email_body)
# Hello $username, welcome back on $login_date. Contact us at $support_link
Best practices make Template usage safe, readable, and effective. Prefer .safe_substitute() with untrusted or partial data — avoids KeyError crashes. Use Template for user/config-provided templates — prevents injection (no expression eval like f-strings). Modern tip: use Polars for large templated columns — pl.col("template").map_elements(lambda t: Template(t).safe_substitute(data)) works but prefer f-strings or .str.format() for speed. Add type hints — str — improves readability and mypy checks. Combine with dict.get() — Template(t).safe_substitute(data.get) for default values. For complex formatting, switch to f-strings or .format() — Template lacks specifiers (alignment, precision). Avoid Template for performance-critical loops — f-strings are faster. Use Template with string.Template — no external dependencies. Handle missing keys gracefully — safe_substitute() leaves $var intact for debugging or partial fills.
The Template method offers safe, predictable string substitution — ideal for user templates, configs, or secure environments. In 2026, use .safe_substitute() for robustness, prefer f-strings for speed/readability, vectorize in pandas/Polars when scaling, and add type hints for safety. Master Template, and you’ll handle dynamic, user-driven text substitution cleanly and securely.
Next time you have a template from config or user input — reach for string.Template. It’s Python’s cleanest way to say: “Substitute these values safely, no code execution.”