Python TypeError：不可散列的类型：“工作日”

Question

I'm trying to generate a human-friendly string representation for a list of dateutil.rrule.weekday objects. To this end, I'm trying to create a dictionary WEEKDAY_TO_NAME which maps the object to its string representation:

import dateutil.parser
from dateutil.rrule import weekdays as WEEKDAYS
WEEKDAY_NAMES = [name[1] for name in dateutil.parser.parserinfo.WEEKDAYS]

WEEKDAY_TO_NAME = dict(zip(WEEKDAYS, WEEKDAY_NAMES))

However, this leads to a

TypeError: unhashable type: 'weekday'

Is there any way to get around this (without writing seven if / elif statements)?

Answer 1

In Python 3, you need to convert the items in WEEKDAYS to strings:

>>> dict(zip(map(str,WEEKDAYS), WEEKDAY_NAMES))
{'SA': 'Saturday', 'TH': 'Thursday', 'SU': 'Sunday', 'WE': 'Wednesday', 'TU': 'Tuesday', 'MO': 'Monday', 'FR': 'Friday'}

Note the type() of item in WEEKDAYS before conversion is 'dateutil.rrule.weekday' :

>>> [type(item) for item in WEEKDAYS]
[<class 'dateutil.rrule.weekday'>, <class 'dateutil.rrule.weekday'>, <class 'dateutil.rrule.weekday'>, <class 'dateutil.rrule.weekday'>, <class 'dateutil.rrule.weekday'>, <class 'dateutil.rrule.weekday'>, <class 'dateutil.rrule.weekday'>]

(Thanks to hascode55 and MSeifert for pointing out that the tuple() calls I had before were unnecessary.)

Answer 2

I should have perhaps been more clear about what I wanted to achieve: a function weekday_to_string which takes an instance of dateutil.rrule.weekday as input and returns a string such as "Monday". I wanted to use the dictionary as a lookup table inside this function, so it actually would not do to convert the dateutil.rrule.weekday instances to strings first since then I would not be able to look up the input anymore.

Here is how I implemented it in the end:

def weekday_to_string(weekday):
    '''Converts a dateutil.rrule weekday constant to its full string representation.'''
    WEEKDAY_NAMES = [name[1] for name in dateutil.parser.parserinfo.WEEKDAYS]
    return WEEKDAY_NAMES[WEEKDAYS.index(weekday)]