Python placeholders in read text

Question

I am fairly new to Python, teaching it to myself by watching tutorials and doing the trial and error kind of thing, and I ran into a task, which I am not able to solve right now:

I am reading from a file with following code:

def read_file(file):
    try:
        with open(file) as f:
            content = f.read()
            return content
    except FileNotFoundError:
        print("\nThis file does not exist!")
        exit()

The file(.txt) I am reading contains a text with multiple placeholders:

Hello {name}, you are on {street_name}!

Now I want to replace the placeholders {name} and {street_name} with their corresponding variables.

I know how f-strings work. Can this somehow be applied to this problem too, or do I have to parse the text to find the placeholders and somehow find out the fitting variable that way?

Each text I read, contains different placeholders. So I have to find out, which placeholder it is and replace it with the according string.

Answer 1

Not sure if that is what you are looking for:

string = "Hello {name}, you are on {street_name}!"
string = string.format(name="Joe", street_name="Main Street")
print(string)

or

string = "Hello {name}, you are on {street_name}!"
name = "Joe"
street_name = "Main Street"
string = string.format(name=name, street_name=street_name)
print(string)

gives you

Hello Joe, you are on Main Street!

See here.

If you actually don't know what placeholders are in the text then you could do something like:

import re

string = "Hello {name}, you are on {street_name}!"
name = "Joe"
street_name = "Main Street"

placeholders = set(re.findall(r"{(\w+)}", string))
string = string.format_map({
    placeholder: globals().get(placeholder, "UNKOWN")
    for placeholder in placeholders
})

If you know that all placeholders are present as variables, then you could simply do:

string = "Hello {name}, you are on {street_name}!"
name = "Joe"
street_name = "Main Street"

string = string.format_map(globals())