Condensing Multiple List Comprehensions

Question

I have a list with input in this form:

open_info = ['Cube 1, 9:30am to 10:00am, Thursday, March 3, 2016', 'Cube 2, 5:00pm to 5:30pm, Thursday, March 3, 2016']

I want to parse through this information to create a new list in this form:

open_times = [[9, 30, 'am'],[5, 0, 'pm']]

With the hour at first index, minutes at second, and am/pm at the third index. I am only recording the first time value for each list element, because the intervals I am dealing with are always 30 minutes long.

I have accomplished this by using the following python list comprehensions:

open_times = [x.split(",")[1].replace(" ","").split("to") for x in open_info]
open_times = [x[0].split(":")+x[1].split(":") for x in open_times]
open_times = [[int(x[0]),int(x[1][:2]),x[1][2:]] for x in open_times]

I was wondering if there was to create a nested list comprehension out of all of these. I've looked at the python documentation and read some blogs on the subject but I'm still having trouble accomplishing this.

Answer 1

To answer the question of how to 'nest' list comprehensions, you might do this to combine lines 1 and 2....

open_times = [y[0].split(":")+y[1].split(":") for y in [x.split(",")[1].replace(" ","").split("to") for x in open_info]]

... but this is really messy. The 3 lines are more understandable and cleaner here. You might also think about writing this as a series of loops since there's a lot going on inside the comprehension that would be cleaner outside of one.

Answer 2

You could use the following:

open_info = ['Cube 1, 9:30am to 10:00am, Thursday, March 3, 2016', 'Cube 2, 5:00pm to 5:30pm, Thursday, March 3, 2016']

answer = [[int(s.split(':',1)[0][-2:]), int(s.split(':')[1][:2]), 
           s.split(':')[1][2:4]] for s in open_info]
print(answer)

Output

[[9, 30, 'am'], [5, 0, 'pm']]

In these circumstances, however, it may be more readable to use map instead of a list comprehension:

def func(s):
    hour = int(s.split(':')[0][-2:])
    minute = int(s.split(':')[1][:2])
    suffix = s.split(':')[1][2:4]
    return [hour, minute, suffix]

answer = map(func, open_info)
print(answer)

Output

[[9, 30, 'am'], [5, 0, 'pm']]