Resolving a variable dynamically in python

Question

Say I have a string -

my_str = "From {country} with Love"

Variable country is not available at the moment and is set at a later stage to

country = "Russia".

Now Can I print string with the inline variable value dynamically resolved. Something like -

print(f"{my_str}")

which will output

From Russia with Love

I tried to use eval() but didn't help.

Is that what you mean: https://stackoverflow.com/questions/42497625/how-to-postpone-defer-the-evaluation-of-f-strings — Thierry Lathuille, Aug 06 '20 at 18:29
actually no, u have to say `my_str = f"From {country} with Love"` then u can proceed as said in the Q and the output will be fine — Delrius Euphoria, Aug 06 '20 at 18:34

Andreas · Answer 1 · 2020-08-06T18:40:51.137

6

my_str = "From {} with Love"
country = "Russia"
print(my_str.format(country))

If you like to work with names you can also do:

my_str = "From {country} with Love"
country = "Russia"
print(my_str.format(country=country))

edited Aug 06 '20 at 18:40

answered Aug 06 '20 at 18:28

Andreas

2

this is the correct answer. – JarroVGIT Aug 06 '20 at 18:30
why not use `f` strings, there is no harm, except for compatiblity with python 2.x – Delrius Euphoria Aug 06 '20 at 18:32
1

Thanks @Andreas, exactly what I was looking for. Didn't know that we can use it based on names as well. – VK. Aug 06 '20 at 18:42
1

@NEO Glad I could help, happy coding! – Andreas Aug 06 '20 at 18:44
@Cool Cloud An f-string is syntax I don't think you will be able to generate syntax through a string. – Andreas Aug 06 '20 at 18:45
hmmm? what to do you mean? – Delrius Euphoria Aug 06 '20 at 18:46
Look at the answer of Eugene Anufriev, he asked the same and found a post with a good explaination. – Andreas Aug 06 '20 at 18:55

score 1 · Answer 2 · answered Aug 06 '20 at 18:33

1

I would suggest using Templating for example Pythons built in templating:

from string import Template

t = Template("From $country with Love")
s = t.substitute(country="Russia")
print(s)

answered Aug 06 '20 at 18:33

jasLogic

score 0 · Answer 3 · answered Aug 06 '20 at 18:27

0

You can create the variable like this:

my_str = f"From {country} with Love"

Then when the country variable gets assigned it will be replaced automatically in the my_str variable.

answered Aug 06 '20 at 18:27

pacuna

3

Note that this will raise an NameError when you try to print the string without initiating the variable `country`. – JarroVGIT Aug 06 '20 at 18:29
Correct @DjerroNeth, I get the error ```NameError: name 'country' is not defined```. @pacuna I don't have the variable set while assigning my_str. It becomes available at a later stage. – VK. Aug 06 '20 at 18:35

score 0 · Answer 4 · answered Aug 06 '20 at 18:30

0

This should work

variable = "Russia"
print(f'my country is {variable} and I live in it')

answered Aug 06 '20 at 18:30

Johnny_Mali39

score 0 · Answer 5 · answered Aug 06 '20 at 18:31

0

This should work too:

country = "Russia"
my_str = f"From {country} with Love"
print(f"{my_str}")

answered Aug 06 '20 at 18:31

Eugene Anufriev

For f-string you have to initialize "country" before the string. also you then could simply do: print(my_str) – Andreas Aug 06 '20 at 18:33
Thanks, good point. Btw, can f-strings be used for a variable definition like in the example I've posted above? – Eugene Anufriev Aug 06 '20 at 18:44
I don't think so because as far as I am aware f strings are syntax not objects. And are most likely not be able to manipulate sytax through a string. – Andreas Aug 06 '20 at 18:47
heh, I think I found the answer here: https://stackoverflow.com/questions/41306928/why-dont-f-strings-change-when-variables-they-reference-change – Eugene Anufriev Aug 06 '20 at 18:52
ah, good explaination, far better then I could do :P – Andreas Aug 06 '20 at 18:55

score 0 · Answer 6 · answered Aug 06 '20 at 18:34

0

Here's an idea:

def str(country):
  my_str="From %s with Love" %country
  print(my_str)
str("Russia")

This will print From Russia with Love.

answered Aug 06 '20 at 18:34

CosmoCoder123

6 Answers6