24-Hour Time Conversion to 12-Hour Clock (ProblemSetQuestion) on Python

Question

I am a beginner programmer in Python and I have no idea how to proceed with the following question. There are a ton of similar questions out there, however there are none having to do with Python code.

I have tried to compare the strings but I am uncertain how to make the comparison. I'm pretty sure I need to take the first two numbers (hours) and divide by 12 if it is greater than 12 ... but that presents problems.

Question:

Time Conversion (24hrs to 12hr)

Write a function that will allow the user to convert the 24 hour time format to the 12 hour format (with 'am','pm' attached). Example: from '1400' to '2:00pm'. All strings passed in as a parameter will have the length of 4 and will only contain numbers.

Examples (tests/calls):

>>> convertTime('0000') 
'12:00am' 
>>> convertTime('1337') 
'1:37pm' 
>>> convertTime('0429') 
'4:29am' 
>>> convertTime('2359') 
'11:59pm' 
>>> convertTime('1111') 
'11:11am'

Any input or different methods would be awesome!

Answer 1

You could use the datetime module, but then you would have to deal with dates as well (you can insert wathever you want there). Probably easier to simply parse it.

---

Update: As @JonClements pointed out in the comments to the original question, it can be done with a one liner:

from datetime import datetime

def convertTime(s):
    print datetime.strptime(s, '%H%M').strftime('%I:%M%p').lower()

---

You can split the input string in the hours and minutes parts in the following way:

hours = input[0:2]
minutes = input[2:4]

And then parse the values to obtain an integer:

hours = int(hours)
minutes = int(minutes)

Or, to do it in a more pythonic way:

hours, minutes = int(input[0:2]), int(input[2:4])

Then you have to decide if the time is in the morning (hours between 0 and 11) or in the afternoon (hours between 12 and 23). Also remember to treat the special case for hours==0:

if hours > 12:
    afternoon = True
    hours -= 12
else:
    afternoon = False
    if hours == 0:
        # Special case
        hours = 12

Now you got everything you need and what's left is to format and print the result:

print '{hours}:{minutes:02d}{postfix}'.format(
    hours=hours,
    minutes=minutes,
    postfix='pm' if afternoon else 'am'
)

Wrap it up in a function, take some shortcuts, and you're left with the following result:

def convertTime(input):
    h, m = int(input[0:2]), int(input[2:4])

    postfix = 'am'

    if h > 12:
        postfix = 'pm'
        h -= 12

    print '{}:{:02d}{}'.format(h or 12, m, postfix)

convertTime('0000') 
convertTime('1337') 
convertTime('0429') 
convertTime('2359') 
convertTime('1111') 

Results in:

12:00am
1:37pm
4:29am
11:59pm
11:11am