passing python parameters into a string which will be used as a python parameter

Question

I am trying to pass python from a string in a web form with other inputs as optional parameters. I am using flask and all the values arrive at a python program as strings. I would like to do something like this. I suspect the whole idea is impossible :)

Any ideas Stack ??

parameter_1 = "Foo"
parameter_2 = "Bar"
sql_string = 'Hello {parameter_1} this is  {parameter_2}; '
formatted_sql = f'''{sql_string}'''
print(sql_string)
print(formatted_sql)

Answer 1

You can use .format():

parameter_1 = "Foo"
parameter_2 = "Bar"
sql_string = 'Hello {p1} this is {p2}'
formatted = sql_string.format(p1=parameter_1, p2=parameter_2)
print(sql_string)
print(formatted)

This also allows sql_string to be used repeatedly, with different parameters.

Answer 2

Python is quite.. dynamic. You can use locals() to get a dict of the local variables. Then use str.format() to apply to the template (it will not be a f-string):

parameter_1 = "Foo"
parameter_2 = "Bar"
sql_string = 'Hello {parameter_1} this is {parameter_2}; '
formatted_sql = sql_string.format(**locals())
print(sql_string)
print(formatted_sql)

This will output:

Hello {parameter_1} this is {parameter_2};
Hello Foo this is Bar;

Now.. it WOULD be a better idea to just define the replacement variables directly as a dict such as:

tvars = { 'parameter_1': 'Foo', 'parameter_2': 'Bar' }
formatted_sql = sql_string.format(**tvars)