A second improvement is possible. Looking at our program we see that several
calculations are performed more than once, i.e. (24 * 60 * 60) and
(60 * 60). There should be a way to avoid the unnecessary
recalculation, and there is. All we have to do is to calculate the quantities
and store them so we can reuse the pre-calculated quantity. We could store them
in a variable, but the quantity shouldn't change, so it would be
wise to prevent it from changing if we can.
A second small concern is that it may not be clear to a someone reading our
program (say someone maintaining it, or even ourselves rereading it a few
months later) what the quantity 60 * 60 is.
Python has a convention we will adhere to to help deal with these issues. We will calculate our reused values once near the top of the program and give them names in all caps to indicate that these values are intended to remain unchanged.
SECS_PER_DAY = 24 * 60 * 60
SECS_PER_HOUR = 60 * 60
SECS_PER_MINUTE = 60
days = tot_seconds / SECS_PER_DAY
remainder = tot_seconds % SECS_PER_DAY
hours = remainder / SECS_PER_HOUR
remainder = remainder % SECS_PER_HOUR
minutes = remainder / SECS_PER_MIN
remainder = remainder % SECS_PER_MINNotes:
By convention constants are given capitalized names. This makes them stand out, and serves as a cue for people reading the program to the fixed nature of the quantity.
These quantities are called symbolic constants, because we get to label them symbolically, i.e. we get to name them. The advantage of naming them is increased readability. Readers may not know what 24*60*60 is but SECS_PER_DAY will be meaningful to most.
Putting all these changes together and adding the declarations, overhead, and some instructions gives us the following complete program.
# s2dhms.py -- converts a time in seconds to
# its equivalent in days, hours, minutes and seconds.
#
# CPSC 128 Demonstration Program
#
# Tim Topper, Winter 2013
SECS_PER_DAY = 24 * 60 * 60
SECS_PER_HOUR = 60 * 60
SECS_PER_MINUTE = 60
# Input.
print "====================================================="
print " Seconds to Days, Hours, Minutes and Seconds"
print "-----------------------------------------------------"
print
print "This program converts a number of seconds to its"
print "equivalent in days, hours, minutes and seconds.";
tot_seconds = input("Enter the number of seconds now (e.g. 116529): ")
print
# Processing.
days = tot_seconds / SECS_PER_DAY
remainder = tot_seconds % SECS_PER_DAY
hours = remainder / SECS_PER_HOUR
remainder = remainder % SECS_PER_HOUR
minutes = remainder / SECS_PER_MINUTE
remainder = remainder % SECS_PER_MINUTE
# Output.
print tot_seconds, "seconds =", days, "days,", hours, "hours,",
print minutes, "minutes and", remainder, "seconds"
Notes:
Note the effect of the trailing comma in the second last line. Try removing it and see how the output changes. How would you describe what this comma does?
Note the blank print statements, i.e. print
statements with no items following them, used to output blank lines.
Symbolic constants can be used to avoid repeating calculations unnecessarily and to increase readability. They are identified by being given names in ALLCAPS.