为什么在尝试与字典值进行比较时出现错误？

Question

I'm supposed to:

Write a function, precipiation(d, a, b) that takes parameters:

d: Dictionary mapping a season to an amount of precipitation for that season. a: One season b: Another season

Your function should return True if the rainfall in season a was greater than it was in season b, and False otherwise. If the rainfall was equal, return False.

Your function should handle the following errors the following ways:

If either a or b is not a valid season in the dictionary, you should return an error message (as a string) formatted exactly as: "Error: Key is not in Dictionary."

If the values for the rainfall in each season are not valid for comparison, that is, one of them is not a number, return an error message (as a string) formatted exactly as: "Error: Invalid data types in Dictionary?"

You may assume that no test case will produce both types of errors (so you do not need to decide whether or not to return a Key Error or Invalid Type error when you encounter both). However, you should not make any assumptions about the seasons that exist--sometimes there may be a 'potato' season.

I wrote a function that is mostly correct

def precipitation(d, a, b):

    try:
        if d[a] > d[b]:
            return True
        else:
            return False

    except:
        if a not in d or b not in d:
            return ("Error: Key is not in Dictionary.")

        if d[a] not in (int) or d[b] not in (int):
            return ("Error: Invalid data types in Dictionary?")

When I run this function with test case

precipitation({"Spring": 'cats', "Summer": 313, "Fall": 1457, "Winter": 354}, "Summer", "Spring") == 'Error: Invalid data types in Dictionary?'

I get an error argument of type 'type' is not iterable How can I fix this and what is causing the problem

Answer 1

This is your problem:

if d[a] not in (int) 

int is not a container, it's a type, so d[a] can't be in it.*

Are you trying to make sure it's an integer? Then try isinstance() :

if not isinstance(d[a], int) ...

* You could write a metaclass that had a __contains__() method that let you treat types as containers and check for instance types in this way, which is actually a kind of interesting idea, but int does not do that.

Answer 2

In addition to the correct answers already provided,
since you are using try and except , you can also specify the type of exception for each block as well:

def precipitation(d, a, b):
    try:
        return d[a] > d[b]
    except KeyError:
        return "Error: Key is not in Dictionary."
    except TypeError:
        return "Error: Invalid data types in Dictionary?"

Answer 3

To check if a parameter is a specific type, use isinstance - in checks if a specific value is present in an iterable.

if not isinstance(d[a], int) or not isinstance(d[b], int):
    return ("Error: Invalid data types in Dictionary?")

Answer 4

use this as this is exact way of error handling

if ValueError:
    return ("Error: Invalid data types in Dictionary?")

instead of

if if d[a] not in (int) or d[b] not in (int):
    return ("Error: Invalid data types in Dictionary?")