pythonfunction-calls

Call a built-in function with a string in Python

I've referred to the following threads and I don't think that this post is a duplicate of any of them:

  1. Calling a function of a module by using its name (a string)
  2. Python Call Function from String
  3. Use a string to call function in Python

For instance, assume that I have a string, data_type = "int", and I want to call the built-in function int directly with the string. BTW I cannot have data_type = int because data_type is actually loaded from a JSON file, i.e. data_type is always a string or None.

My best (neatest) attempt is eval(data_type)("4"), but as people suggested, eval doesn't seem to be a good option and should be avoided whatever.

An alternative is creating a dictionary like data_type_dic = {"int": int, "float": float} and executing data_type_dic[data_type]("4"). However, creating that dictionary feels like "reinventing the wheel" to me.

Since int is a built-in function, not a method in a module, so getattr seems unworkable. It is not a self-defined function either, so locals()[data_type] gives KeyError.

What is the best way to call a built-in function with the corresponding string then?

Solution

  • The best way is still a dictionary, but:

    >>> import builtins
>>> getattr(builtins, 'int')
<class 'int'>