🔒 CS50 [working.py] regex value question | Python | Page 1

slate wraith Sep 19, 2024, 1:36 PM

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Hello again everyone, I'm currently working on the CS50 Python course's working.py assignment, and while I've figured it out for the most part, I have a silly problem I would like some advice on.

First, here is my code:

import re

def main():
    print(convert(input("Hours: ")))

def convert(s):
    if time := re.search(r"(\d{1,2}):?(\d{2})? (AM|PM) to (\d{1,2}):?(\d{2})? (AM|PM)", s, re.IGNORECASE):
        h1, h2 = (int(time.group(1)), int(time.group(4)))
        m1, m2 = (int(time.group(2)), int(time.group(5)))
        p1, p2 = (time.group(3), time.group(6))
        if any((h1, h2)) > 12 and any((m1, m2)) >= 60:
            raise ValueError
        if h1 < 12 and p1 == "PM":
            h1 += 12
        if h2 < 12 and p2 == "PM":
            h2 += 12
        if h1 == 12 and p1 == "AM":
            h1 -= 12
        if h2 == 12 and p2 == "AM":
            h2 -= 12
        if m1 == None:
            m1 = ":00"
        if m2 == None:
            m2 = ":00"
        return f"{h1:02d}:{m1:02d} to {h2:02d}:{m2:02d}"
    else:
        raise ValueError

if __name__ == "__main__":
    main()

The assignment calls for a time prompt in the 12-hour format, for example: 9 AM to 5 PM, 9:30 AM to 3:30 PM etc and the output is on the 24-hour format, like 09:00 to 17:00. The problem I'm experiencing is that when the minutes are declared as time.group(2) and time.group(5) respectively but omitted from the prompt, the AM|PM value takes the minute's group position and results in disarray. What would be the best and most efficient way to approach this? And also, if you have any other advice on how to shorten / optimize my code, any advice would be really appreciated as I am still learning, thank you!

dire currentBOT Sep 19, 2024, 1:36 PM

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slate wraith Hello again everyone, I'm currently working on the CS50 Python course's working....

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@slate wraith

Python help channel opened

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#

Hey @slate wraith!

It looks like you pasted Python code without syntax highlighting.

Please use syntax highlighting to improve the legibility of your code and make it easier for us to help you.

To do this, use the following method:
```py
print('Hello, world!')
```

This will result in the following:

print('Hello, world!')```
You can **edit your original message** to correct your code block.

hushed grail Sep 19, 2024, 1:43 PM

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slate wraith Hello again everyone, I'm currently working on the CS50 Python course's working....

I would honestly handle it differently if : is in the time output. Will it ever be 9:00AM to 5PM?

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will they mix and match formats?

slate wraith Sep 19, 2024, 1:51 PM

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They should be separated by space and the user could also choose the opposite, like 5:30 PM to 1 AM

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The assignment also doesn't allow format mixing, other than omitting or inputting the minutes in the prompt

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So it should be something like h(:m) (AM|PM) to h(:m) (AM|PM) sort of thing

hushed grail Sep 19, 2024, 1:55 PM

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Can you give an example prompt that gives the problem result?

slate wraith Sep 19, 2024, 1:56 PM

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Yes, of course, let me produce an error really fast and will copy paste here

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So, writing for example 11 AM to 5 PM produces the following error:

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Hours: 11 AM to 5 PM
Traceback (most recent call last):
  File "/mnt/external/Dropbox/programming/builder/CS50/tests/working3.py", line 30, in <module>
    main()
  File "/mnt/external/Dropbox/programming/builder/CS50/tests/working3.py", line 4, in main
    print(convert(input("Hours: ")))
          ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/mnt/external/Dropbox/programming/builder/CS50/tests/working3.py", line 9, in convert
    m1, m2 = (int(time.group(2)), int(time.group(5)))
              ^^^^^^^^^^^^^^^^^^
TypeError: int() argument must be a string, a bytes-like object or a real number, not 'NoneType'

hushed grail Sep 19, 2024, 1:58 PM

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you could do int(time.group(2) or 0)

slate wraith Sep 19, 2024, 1:58 PM

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This is because there are no minutes written in my prompt, hence the program thinking that the AM|PM thing is time.group(2) instead

hushed grail Sep 19, 2024, 1:59 PM

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your groups shouldn't shuffle around based on the prompt though

slate wraith Sep 19, 2024, 1:59 PM

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That's what I also thought! That's what baffles me

hushed grail Sep 19, 2024, 1:59 PM

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convert("9:30 AM to 3:30 PM")
convert("11 AM to 5 PM")

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I ran these 2 tests

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('9', '30', 'AM', '3', '30', 'PM')
('11', None, 'AM', '5', None, 'PM')

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these are the resulting groups

hushed grail Sep 19, 2024, 2:00 PM

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hushed grail you could do `int(time.group(2) or 0)`

so this trick here basically converts None to 0

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if no minutes, then minutes are 0

slate wraith Sep 19, 2024, 2:00 PM

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Right, that's why I also have this in my code:

if m1 == None:
      m1 = ":00"
if m2 == None:
      m2 = ":00"

dire currentBOT Sep 19, 2024, 2:00 PM

#

Hey @slate wraith!

It looks like you pasted Python code without syntax highlighting.

Please use syntax highlighting to improve the legibility of your code and make it easier for us to help you.

To do this, use the following method:
```py
print('Hello, world!')
```

This will result in the following:

print('Hello, world!')```
You can **edit your original message** to correct your code block.

hushed grail Sep 19, 2024, 2:01 PM

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this lets you catch it a bit earlier and a bit more elegantly

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!e

number1 = '10'
number2 = None

print(int(number1 or 0))
print(int(number2 or 0))

dire currentBOT Sep 19, 2024, 2:01 PM

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hushed grail !e ```py number1 = '10' number2 = None print(int(number1 or 0)) print(int(numbe...

:white_check_mark: Your 3.12 eval job has completed with return code 0.

001 | 10
002 | 0

slate wraith Sep 19, 2024, 2:02 PM

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Hmmmm

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I am a bit confused

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I know the minutes return None if they are non-existent in the prompt

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But I thought writing the two if statements above fixes this

hushed grail Sep 19, 2024, 2:04 PM

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it's because you're trying to convert None to int

slate wraith Sep 19, 2024, 2:04 PM

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Ohhhhhh

hushed grail Sep 19, 2024, 2:04 PM

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hushed grail you could do `int(time.group(2) or 0)`

that's why I suggest this

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then you can completely get rid of the if m1 == None

slate wraith Sep 19, 2024, 2:05 PM

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OH!!!

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I think I get it!

hushed grail Sep 19, 2024, 2:05 PM

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m1, m2 = (int(time.group(2) or 0), int(time.group(5) or 0))

slate wraith Sep 19, 2024, 2:05 PM

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Ohhhhhhhhh

hushed grail Sep 19, 2024, 2:05 PM

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do you understand how or works here?

slate wraith Sep 19, 2024, 2:05 PM

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Yes yes of course

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I just didn't know we could have an or 0 scenario inside a tuple

hushed grail Sep 19, 2024, 2:06 PM

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you can or any expression

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it simply takes the first "truthy" result or the final result

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so if none of the expressions are truthy, it will fall on the last one

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!e

print(0 or [] or None)
print(None or 0 or [])
print(None or 5 or [])

dire currentBOT Sep 19, 2024, 2:07 PM

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hushed grail !e ```py print(0 or [] or None) print(None or 0 or []) print(None or 5 or []) ``...

:white_check_mark: Your 3.12 eval job has completed with return code 0.

001 | None
002 | []
003 | 5

hushed grail Sep 19, 2024, 2:07 PM

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really useful for converting non-truthy data into a format you prefer

slate wraith Sep 19, 2024, 2:08 PM

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Oh wow, that is truly eye-opening

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I had no idea Python was that flexible

hushed grail Sep 19, 2024, 2:08 PM

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I work with a library that unfortunately has a lot of functions that return either a list, or None if no data is found

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so I often do

children = list_relatives(node) or []

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this way I'm forced into an empty list instead of None

slate wraith Sep 19, 2024, 2:09 PM

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Sometimes I also go by spoken logic and fall into human errors, but in reality, Python can understand it all

hushed grail Sep 19, 2024, 2:09 PM

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slate wraith Sometimes I also go by spoken logic and fall into human errors, but in reality, ...

haha to some degree, sure

slate wraith Sep 19, 2024, 2:09 PM

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hushed grail so I often do ```py children = list_relatives(node) or [] ```

Oh I understand that

hushed grail Sep 19, 2024, 2:10 PM

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I used to do this before I learned the "or" trick

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children = list_relatives(node)
if children:
    for child in children:
        ...

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children = list_relatives(node) or []
for child in children:
    ...

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now I can completely cut out the if

slate wraith Sep 19, 2024, 2:10 PM

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Oh yeah I see

hushed grail Sep 19, 2024, 2:10 PM

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if the list is empty, the loop will simply be skipped

slate wraith Sep 19, 2024, 2:10 PM

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Sorry, can I ask one more question?

hushed grail Sep 19, 2024, 2:10 PM

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Sure, go ahead, it's your thread 🙂

slate wraith Sep 19, 2024, 2:11 PM

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The program works perfectly now thanks to your advice, so I also deleted the two if statements, but are there any other refinements I can do to optimize the code without jeopardizing its legibility?

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I am trying to avoid arbitrary steps as much as possible

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This is my code now:

#

import re

def main():
    print(convert(input("Hours: ")))

def convert(s):
    if time := re.search(r"(\d{1,2}):?(\d{2})? (AM|PM) to (\d{1,2}):?(\d{2})? (AM|PM)", s, re.IGNORECASE):
        h1, h2 = (int(time.group(1)), int(time.group(4)))
        m1, m2 = (int(time.group(2) or 0), int(time.group(5) or 0))
        p1, p2 = (time.group(3), time.group(6))
        if any((h1, h2)) > 12 and any((m1, m2)) >= 60:
            raise ValueError
        if h1 < 12 and p1 == "PM":
            h1 += 12
        if h2 < 12 and p2 == "PM":
            h2 += 12
        if h1 == 12 and p1 == "AM":
            h1 -= 12
        if h2 == 12 and p2 == "AM":
            h2 -= 12
        return f"{h1:02d}:{m1:02d} to {h2:02d}:{m2:02d}"
    else:
        raise ValueError

if __name__ == "__main__":
    main()

hushed grail Sep 19, 2024, 2:14 PM

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I think it looks good as it is! For future optimizations, I'd consider using the datetime module to parse the time

slate wraith Sep 19, 2024, 2:14 PM

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Oh okay, this is something I still haven't learned, but noted!

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I feel there's a lot of redundantness in this part in specific:

if h1 < 12 and p1 == "PM":
            h1 += 12
        if h2 < 12 and p2 == "PM":
            h2 += 12
        if h1 == 12 and p1 == "AM":
            h1 -= 12
        if h2 == 12 and p2 == "AM":
            h2 -= 12

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But it doesn't seem like there's much I can do about it, right?

hushed grail Sep 19, 2024, 2:15 PM

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a lot of "redundancies" could be offloaded to a separate function

slate wraith Sep 19, 2024, 2:16 PM

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Oh, right

hushed grail Sep 19, 2024, 2:16 PM

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so you could write another function like "convert_24hr_time"

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and then handle it all there

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it's the same logic, just handled elsewhere

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but it keeps things neater

slate wraith Sep 19, 2024, 2:16 PM

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But it would technically result in the same amount of lines, right?

hushed grail Sep 19, 2024, 2:17 PM

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your convert function would be smaller, but you'd have a new function so it would technically be more lines overall

slate wraith Sep 19, 2024, 2:17 PM

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Right, I understand

hushed grail Sep 19, 2024, 2:17 PM

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but then you wouldn't need an if for your times

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you'd just say

h1 = convert_24hr_time(h1, p1)
h2 = convert_24hr_time(h2, p2)

slate wraith Sep 19, 2024, 2:17 PM

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Ahhh right, yes

hushed grail Sep 19, 2024, 2:18 PM

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learning how to split code up into smaller functions becomes very important

slate wraith Sep 19, 2024, 2:18 PM

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I am still not used to writing separate functions for separate purposes, but I probably should get used to it, as programs become more complex

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Yes, exactly

hushed grail Sep 19, 2024, 2:19 PM

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you're always better off having 3 separate smaller functions rather than 1 mega function that does 3 things

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then you just have 1 function call those 3 functions

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it makes things more modular and reusable

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it's ok if you don't write it that way all on the first go though

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this is where refactoring becomes important

slate wraith Sep 19, 2024, 2:20 PM

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I think I will try to rewrite this program now with a new convert24h function, just to practice common Python nomenclature

hushed grail Sep 19, 2024, 2:20 PM

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and yeah, datetime would be good practice too

slate wraith Sep 19, 2024, 2:21 PM

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I would also like to eventually work with other people in software, so I want to refine my Python skills and its legibility as much as possible

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For now, thank you so much for all your help!

hushed grail Sep 19, 2024, 2:21 PM

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np!

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I can show a datetime example if you like

slate wraith Sep 19, 2024, 2:21 PM

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I learned a ton today, thank you so much

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Oh, if that's no trouble for you, yes please

hushed grail Sep 19, 2024, 2:22 PM

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('9', '30', 'AM', '3', '30', 'PM')

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I'm just going to use this as the initial example

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because you already have this data easily accessible

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the first 3 indices will be the 1st time and the next 3 will be the 2nd time

slate wraith Sep 19, 2024, 2:23 PM

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Ohhh

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Is this a builtin Python function?

hushed grail Sep 19, 2024, 2:24 PM

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you need to import it, but yeah, it's part of the standard library

slate wraith Sep 19, 2024, 2:24 PM

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Or a library?

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Ohhh okay

hushed grail Sep 19, 2024, 2:24 PM

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it can be a bit confusing at first because the module and class name are the same

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so from datetime import datetime is commonly how you import it

slate wraith Sep 19, 2024, 2:25 PM

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In order to avoid that whole datetime.datetime() type of thing, I'd imagine

hushed grail Sep 19, 2024, 2:25 PM

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exactly

slate wraith Sep 19, 2024, 2:25 PM

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Yeah

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Wow, Python has libraries for everything nowadays

hushed grail Sep 19, 2024, 2:25 PM

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so with datetime, there's a formatting syntax that lets us convert a string into a "datetime object"

slate wraith Sep 19, 2024, 2:25 PM

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But it feels good to have figured this out the regex way

hushed grail Sep 19, 2024, 2:25 PM

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but we need to tell it exactly how our string looks

hushed grail Sep 19, 2024, 2:25 PM

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slate wraith But it feels good to have figured this out the regex way

yeah it's a good solve

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I would still use regex to parse the text

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but then you can feed that information into the datetime string and let it figure out the conversion

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!e

from datetime import datetime

times = ('9', '30', 'AM', '3', '30', 'PM')
t1, t2 = times[:3], times[3:]

print(t1)
print(t2)

dire currentBOT Sep 19, 2024, 2:26 PM

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hushed grail !e ```py from datetime import datetime times = ('9', '30', 'AM', '3', '30', 'PM...

:white_check_mark: Your 3.12 eval job has completed with return code 0.

001 | ('9', '30', 'AM')
002 | ('3', '30', 'PM')

hushed grail Sep 19, 2024, 2:26 PM

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so I start by splitting up the 2 times, but unfortunately datetime doesn't like digits that aren't padded

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it wants 09, not 9

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we can do this in a super lazy way using a list comp or the map function

slate wraith Sep 19, 2024, 2:27 PM

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Yeah, cause the assignment still called for a py f"{datetime[0]}:{datetime[1]} to {datetime[3]}:{datetime[4]}" type of thing

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This is probably wrong, but

hushed grail Sep 19, 2024, 2:28 PM

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!e

from datetime import datetime

times = ('9', '30', 'AM', '3', '30', 'PM')
t1, t2 = times[:3], times[3:]

print([f'{i:>02}' for i in t1])
print([f'{i:>02}' for i in t2])

dire currentBOT Sep 19, 2024, 2:28 PM

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hushed grail !e ```py from datetime import datetime times = ('9', '30', 'AM', '3', '30', 'PM...

:white_check_mark: Your 3.12 eval job has completed with return code 0.

001 | ['09', '30', 'AM']
002 | ['03', '30', 'PM']

hushed grail Sep 19, 2024, 2:28 PM

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so this solves the zero-padding issue

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but now we also need a string

slate wraith Sep 19, 2024, 2:28 PM

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Ohhhhh

hushed grail Sep 19, 2024, 2:28 PM

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we can use str.join to make a string from this

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!e

from datetime import datetime

times = ('9', '30', 'AM', '3', '30', 'PM')
t1, t2 = times[:3], times[3:]

print('-'.join([f'{i:>02}' for i in t1]))
print('-'.join([f'{i:>02}' for i in t2]))

dire currentBOT Sep 19, 2024, 2:29 PM

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hushed grail !e ```py from datetime import datetime times = ('9', '30', 'AM', '3', '30', 'PM...

:white_check_mark: Your 3.12 eval job has completed with return code 0.

001 | 09-30-AM
002 | 03-30-PM

hushed grail Sep 19, 2024, 2:29 PM

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this is good enough for datetime to start working with

slate wraith Sep 19, 2024, 2:29 PM

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Wow, this is so great, this could come in very handy in the future

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Thank you so much for all your help today

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I genuinely appreciate it you taking the time to help me out

hushed grail Sep 19, 2024, 2:30 PM

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np!

slate wraith Sep 19, 2024, 2:30 PM

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!close

dire currentBOT Sep 19, 2024, 2:30 PM

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#🔒 CS50 [working.py] regex value question