How to filter an unknown element in a list python

Question

I'm trying to make a program that is given abbreviations of the days of the week (Mon, Tue, Wed etc.) and replaces these with the full word (Monday, Tuesday, Wednesday). The program creates a list full of strings and outputs it as a string. I have this working except for when something that isn't a day of the week is used. For example, a word that isn't Mon, Tue, Wed etc. (As seen in the code) I want to be able to filter out the unwanted word but don't know how to. Please help.

The code:

days = []

def format_days(days): 

  days = [d.replace('Mon', 'Monday') for d in days]
  days = [d.replace('Tue', 'Tuesday') for d in days]
  days = [d.replace('Wed', 'Wednesday') for d in days]
  days = [d.replace('Thu', 'Thursday') for d in days]
  days = [d.replace('Fri', 'Friday') for d in days]
  days = [d.replace('Sat', 'Saturday') for d in days]
  days = [d.replace('Sun', 'Sunday') for d in days]


  return days

answer = format_days(['Sat', 'Fun', 'Tue', 'Thu'])
print(answer)

# ['Saturday', 'Fun', 'Tuesday', 'Thursday'] <-- This is the output

# ['Saturday', 'Tuesday', 'Thursday'] <-- This is the output I want

I want to be able to filter out 'fun' from the list but the code needs to work for everything that isn't: Mon, Tue, Wed, Thu, Fri, Sat, Sun not just 'fun'

What was the problem when you tried to do it? Did you try using something some sort of if statement? — mkrieger1
– mkrieger1, Commented Mar 16, 2020 at 11:04

yatu · Accepted Answer · 2020-03-16 11:15:14Z

3

I'd suggest you a different approach for this. Start by defining a dictionary mapping the three first letters of a day to the entire name:

days_of_week = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday', 'Sunday']
d = {day[:3]:day for day in days_of_week}

print(d)

{'Mon': 'Monday',
 'Tue': 'Tuesday',
 'Wed': 'Wednesday',
 'Thu': 'Thursday',
 'Fri': 'Friday',
 'Sat': 'Saturday',
 'Sun': 'Sunday'}

And use a list comprehension with a conditional statement so that nothing is returned if a given case is not found in the dictionary:

[d.get(i) for i in ['Sat', 'Fun', 'Tue', 'Thu'] if i in d]
# ['Saturday', 'Tuesday', 'Thursday']

edited Mar 16, 2020 at 11:15

answered Mar 16, 2020 at 11:05

yatu

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4 Comments

mkrieger1 Over a year ago

Then why did you post it if it is the same as the (two!) existing other answers?

yatu Over a year ago

It was posted more or less on the same time (I tool longer since I took my time in adding explanations) @mkrieger1

RoadRunner Over a year ago

Nice answer. I was lazy and just used the calendar module instead. Also not sure why you need get(i) here since you already checking if i in d. get() returns None if the key is not found by default, but that will never happen if i in d is True anyways. Correct me if wrong.

yatu Over a year ago

Yes you're right. Left it there cause I was thinking of doing it differently I think :) but youre right, not really necessary @road

Ch3steR · Accepted Answer · 2020-03-16 11:04:03Z

2

You can make a dictionary of valid words. If anything other than a valid day is encountered it's ignored.

def fromat_days(days):
    valid_days={'Mon':'Monday',
                'Tue':'Tuesday',
                 ...
                'Sun':'Sunday'}
    return [valid_days[day] for day in days if day in valid_days]

answered Mar 16, 2020 at 11:04

Ch3steR

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3 Comments

Ch3steR Over a year ago

Glad to help ;) @skribbsta

RoadRunner Over a year ago

@Ch3steR I have the same question.

Ch3steR Over a year ago

@RoadRunner Looks like someone's on a downvoting spree. ;)

RoadRunner · Accepted Answer · 2020-03-16 11:26:10Z

2

Adding to others answers, you could also use the calendar functions day_name and day_abbr to zip() day abbreviations and full weekday names:

from calendar import day_abbr, day_name

day_map = dict(zip(day_abbr, day_name))

days = ['Mon', 'Wed', 'Fri', 'Sat']

print([day_map[d] for d in days if d in days])
# ['Monday', 'Wednesday', 'Friday', 'Saturday']

This is helpful because you don't have to generate the day dictionary yourself.

edited Mar 16, 2020 at 11:26

answered Mar 16, 2020 at 11:21

RoadRunner

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1 Comment

Ch3steR Over a year ago

Nice answer. Never knew the calender module. +1

a_guest · Accepted Answer · 2020-03-16 11:04:39Z

1

You can start with a mapping from abbreviations to full names and then only replace if the abbreviation is present in the mapping:

map_to_names = {'Mon': 'Monday', 'Tue': 'Tuesday', ..., 'Sun': 'Sunday'}
result = [map_to_names[s] for s in days if s in map_to_names]

answered Mar 16, 2020 at 11:04

a_guest

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Comments

kederrac · Accepted Answer · 2020-03-16 11:50:25Z

0

you can store in a dict the mapping btw the first 3 characters and the day:

w_day = {'Mon': 'Monday',
 'Tue': 'Tuesday',
 'Wed': 'Wednesday',
 'Thu': 'Thursday',
 'Fri': 'Friday',
 'Sat': 'Saturday',
 'Sun': 'Sunday'}

def format_days(days): 
    return list(filter(None, map(w_day.get, days)))

format_days(['Sat', 'Fun', 'Tue', 'Thu'])

output:

['Saturday', 'Tuesday', 'Thursday']

edited Mar 16, 2020 at 11:50

answered Mar 16, 2020 at 11:23

kederrac

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