Leverage Python f-strings with Yaml files?

Question

If I have a yaml file containing a string with the bracket notation {} used in partnership with python f-strings, how might a leverage the f-string interpolation here? Take for example this simple yaml file:

# tmp.yaml
k1: val1
k2: val2 as well as {x}

If x = 'val3', I would like the value of the k2 to reflect val2 as well as val3

# app.py
x = 'val3'
with open('tmp.yaml', 'rt') as f:
    conf = yaml.safe_load(f)

print(conf)
{'k1': 'val1', 'k2': 'val2 as well as {x}'}

This could be accomplished pretty easily with format strings...

print(conf['k2'].format(x=x))
val2 as well as val3

But how to do the same with f-strings?

Answer 1

I found that jinja2 provides the easiest solution to this problem.

Source yaml file:

# tmp.yaml
k1: val1
k2: val2 as well as {{ x }}

Read the file and render using jinja templating:

with open('tmp.yaml', 'rt') as f:
    conf = f.read().rstrip()

print(conf)
# 'k1: val1\nk2: val2 as well as {{ x }}'

import jinja2
template = Template(conf)
conf = template.render(x='val3')
config = yaml.safe_load(conf)

print(config)
# {'k1': 'val1', 'k2': 'val2 as well as val3'}