How to Defer Evaluation of F-Strings in Python?

Deferring Evaluation of F-Strings

In Python, f-strings offer a succinct way to generate formatted strings. However, sometimes it's useful to define templates elsewhere and import them as static strings. To efficiently evaluate these static strings as dynamic f-strings, we need a way to postpone their evaluation.

While the .format(**locals()) method can be used, it involves explicit variable expansion. To avoid this overhead, consider the following strategy:

<code class="python">def fstr(template):
    return eval(f'f&amp;quot;&amp;quot;&amp;quot;{template}&amp;quot;&amp;quot;&amp;quot;')</code>

This function takes a static template string and constructs an f-string dynamically at runtime. For instance, given the template:

<code class="python">template = "The current name is {name}"</code>

We can evaluate it using:

<code class="python">print(fstr(template))  # Output: The current name is foo</code>

Note that this method also supports expressions within curly braces, as exemplified by:

<code class="python">template = "The current name is {name.upper() * 2}"
print(fstr(template))  # Output: The current name is FOOFOO</code>

By postponing the evaluation of f-strings using the fstr() function, developers can maintain code clarity and simplify template handling in Python.

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