How to type cast a str to another type at runtime [duplicate]-CodePudding

Consider this:

a = "True"
b = bool

How can I convert "a" into a a boolean?

In essence what I am looking for is something like:

a = "True"
b = bool
c = str_to_type(a, b)
print(c)
--> True

a = "1"
b = int
c = str_to_type(a,b)
print(c)
--> 1

And in the event "a" is not compatible with the class specified in "b" then I expect str_to_type to return None.

I'm trying to avoid having to write a if-else block, but if there isn't an elegant way to do this, I'll consider if-else. After all, I'm only looking at a few simple data types: int, float, str, bool. I am not looking to support user-defined classes.

I currently have this implemented:

def str_to_type(value: str, data_type: object):
    if (data_type is bool):
        if value.lower() in ("true"):
            return True
        elif value.lower() in ("false"):
            return False
        else:
            return None
    elif (data_type is int):
        try:
            return int(value)
        except:
            return None
    elif (data_type is float):
        try:
            return float(value)
        except:
            return None
    elif (data_type is str):
        return value
    else:
        return None

CodePudding user response：

I guess you can simply do:

def str_to_type(a, b):
    return b(a)

x = str_to_type('True', bool)
print(type(x), x) # <class 'bool'> True
x = str_to_type('1', int)
print(type(x), x) # <class 'int'> 1

CodePudding user response：

eval is what you might be looking for:

>>> a = "True"
>>> b = bool
>>> b(eval(a))
True
>>> a = "1"
>>> b = int
>>> b(eval(a))
1

Disclaimer:

Most of the time, eval is not the correct solution for your problem. If you tell what is your end goal with this strategy, we might suggest a better approach.