Test in python format string

Question

I have a python string like this:

expression = "test[1]"

var1 = "{%s}" % expression
str1 = f"{var1}"
print(str1.format(test="world"))

I can only change the first line (expression affectation) and i want to test if second character is 'o' inside the expression, in order to display result on console.

if have tried this:

expression = "test[1]=='o'"

expression = "(test[1]=='o')"

expression = "1 if test[1]=='o' else 0"

Nothing works.

Is there a way to do this ?

Thanks

Kirill · Accepted Answer · 2022-08-11 23:02:33Z

0

Try to create your own class that inherits the str class like this:

class MyStr(str):
    def __getattribute__(self, item):
        if "(" in item:
            return eval(f"'{self}'.{item}")
        return str.__getattribute__(self, item)

    def __getitem__(self, item):
        return MyStr(str.__getitem__(self, item))

Use your class in format method argument like this:

expression = "test[1].__eq__('o')"
str1 = f"{{{expression}}}"
print(str1.format(test=MyStr("world")))

Output

True

Be very careful when using the eval method because the usage shown is similar to sql injection.

answered Aug 11, 2022 at 23:02

Kirill

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