Question: How do I transform a classic string to an f-string?

```
variable = 42
user_input = "The answer is {variable}"
print(user_input)

```

Output: `The answer is {variable}`

```
f_user_input = # Here the operation to go from a string to an f-string
print(f_user_input)

```

Desired output: `The answer is 42`

Answer: 
An f-string is **syntax**, not an object type. You can't convert an arbitrary string to that syntax, the syntax creates a string object, not the other way around.

I'm assuming you want to use `user_input` as a template, so just use the [`str.format()` method](https://docs.python.org/3/library/stdtypes.html#str.format) on the `user_input` object:

```
variable = 42
user_input = "The answer is {variable}"
formatted = user_input.format(variable=variable)

```

If you wanted to provide a configurable templating service, create a namespace dictionary with all fields that can be interpolated, and use `str.format()` with the `**kwargs` call syntax to apply the namespace:

```
namespace = {'foo': 42, 'bar': 'spam, spam, spam, ham and eggs'}
formatted = user_input.format(**namespace)

```

The user can then use any of the keys in the namespace in `{...}` fields (or none, unused fields are ignored).
```py
variable = 42
user_input = "The answer is {variable}"
# in order to get The answer is 42, we can follow this method
print (user_input.format(variable=variable))

```

(or)

```py
user_input_formatted = user_input.format(variable=variable)
print (user_input_formatted)

```

Good link <https://cito.github.io/blog/f-strings/>