returning functions from a method in python

Question

I have tried looking into the documentation and google search , but I am unable to find out the significance of the [clazz] at the end of method. Could someone help me understand the meaning of the [clazz] at the end of the method? Thanks.

def get_context_setter(context, clazz):
        return {
            int: context.setFieldToInt,
            datetime: context.setFieldToDatetime
        }[clazz]

setFieldToInt and setFieldToDatetime are methods inside context class.

It looks like it's building a dictionary and then immediately accessing the key passed in as the `clazz` argument. — Patrick Haugh, Nov 15 '16 at 17:18
So you pass it the `int` class or the `datetime` class and it returns a constructor for that context and class — Patrick Haugh, Nov 15 '16 at 17:19

score 1 · Accepted Answer · edited May 23 '17 at 12:01

This function returns one of two things. It returns either context.setFieldToInt or context.setFieldToDatetime. It does so by using a dictionary as what would be a switch statement in other programming languages.

It checks whether clazz is a reference to the class int or a reference to the class datetime, and then returns the appropriate method.

It's identical to this code:

def get_context_setter(context, clazz):
    lookup_table = {int: context.setFieldToInt,
                    datetime: context.setFieldToDatetime
                   }
    context_function = lookup_table[clazz] # figure out which to return
    return context_function

Using a dict instead of a switch statement is pretty popular, see Replacements for switch statement in Python? .

score 0 · Answer 2 · answered Nov 15 '16 at 17:34

More briefly. The code presented is expecting the class of some object as a parameter poorly named as clazz. It's then using that class as a dictionary key. They're essentially trying to accept two different types and call a method on the object type.

class is a keyword in Python. The author of the code you show chose to use a strange spelling instead of a longer snake_case parameter name like obj_class. The parameters really should have been named obj, obj_class Or instance, instance_class

Even better, the class really need not be a separate parameter.

returning functions from a method in python

2 Answers2