How to convert an H:MM:SS time string to seconds in Python?

Using datetime module is also posible and more robust

import datetime as dt

def get_total_seconds(stringHMS):
   timedeltaObj = dt.datetime.strptime(stringHMS, "%H:%M:%S") - dt.datetime(1900,1,1)
   return timedeltaObj.total_seconds()

datetime.strptime parses the string according to format %H:%M:%S, and it creates a datetime object as year 1900, month1, day 1, hour H, minute M, and second S.

That's why to get the total of seconds is necessary to subtract the year, month and day.

print(get_total_seconds('1:23:45'))
>>> 5025.0

print(get_total_seconds('0:04:15'))
>>> 255.0

print(get_total_seconds('0:00:25'))
>>>25.0

You can split the time into a list and add each individual time component, multiplying the hours component by 3600 (the number of seconds in an hour) and the minutes component by 60 (number of seconds in a minute), like:

timeInterval ='00:35:01'
list = timeInterval.split(':')
hours = list[0]
minutes = list[1]
seconds = list[2]
total = (int(hours) * 3600 + int(minutes) * 60 + int(seconds))
print("total = ", total)

For %H:%M:%S.%f

def get_sec(time_str):
    h, m, s = time_str.split(':')
    return int(h) * 3600 + int(m) * 60 + float(s)

Expanding on @FMc's solution which embodies half of Horner's method. Advantage of Horner's method: Skip reversing the list, avoid power calculation.

from functools import reduce

timestamp = "1:23:45"
seconds = reduce(lambda s, d: s * 60 + int(d), timestamp.split(":"), 0)

or, if you dislike reduce (as does Guido van Rossum and @0xc0de below):

timestamp = "1:23:45"
seconds = 0
for d in timestamp.split(":"):
    seconds = seconds * 60 + int(d)

If you prefer zip (as does @nathan-rice below):

from itertools import accumulate, repeat
from operator import mul

def timestamp_to_seconds(t):
    return sum(int(n) * m for n, m in
       zip(reversed(t.split(":")), accumulate(repeat(60), func=mul, initial=1)))

Just a simple generalization to the great response of taskinoor

In the context of my problem the format is similar, but includes AM or PM.

Format 'HH:MM:SS AM' or 'HH:MM:SS PM'

For this case the function changes to:

def get_sec(time_str):
"""Get Seconds from time."""
if 'AM' in time_str:
    time_str = time_str.strip('AM')
    h, m, s = time_str.split(':')
    seconds = int(h) * 3600 + int(m) * 60 + int(s)
if 'PM' in time_str:
    time_str = time_str.strip('PM')
    h, m, s = time_str.split(':')
    seconds = (12 + int(h)) * 3600 + int(m) * 60 + int(s)

return seconds 

In Pandas using @JayRizzo 's cool function and a list comprehension:

def get_sec(time_str):
    """Get Seconds from time."""
    h, m, s = time_str.split(':')
    return int(h) * 3600 + int(m) * 60 + int(s)

df['secs']=[get_sec(x) for x in df['original_time_string']]