[Tutor] scope question

[Norvell Spearman]

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python v2.2.2

I think I'm confused about scope and functions' passing of parameters.
I've been working through the ``How to Think Like a Computer Scientist''
tutorial and up 'til now everything has been fairly clear to me.  The
attached file is what I've typed in from exercises and examples in
Chapter 13, ``Classes and Functions,'' with the last function,
increment, being the one I'm having problems with.  Below is a
transcript from running the program and then manually calling some
functions (in idle):

************************************************
Hours:  4
Minutes:  57
Seconds:  45
Seconds to add to given time:  34
The time is now:   4:57:45
>>> t1 = Time()
>>> t1.hours, t1.minutes, t1.seconds = 4, 57, 45
>>> printTime(t1)
4:57:45
>>> increment(t1, 34)
>>> printTime(t1)
4:57:45
>>> t1 = addTime(t1, makeTime(34))
>>> printTime(t1)
4:58:19
************************************************

My question (finally) is this:  Why doesn't increment alter t1 while
``t1 = addTime(t1, makeTime(34))'' in an interactive session does alter
t1?

Thanks much for any help with this.

-- 
Norvell Spearman

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import copy

class Time:
    pass

def printTime(Time):
    print "%d:%d:%d" % (Time.hours, Time.minutes, Time.seconds)

def convertToSeconds(t):
    minutes = t.hours*60 + t.minutes
    seconds = minutes*60 + t.seconds
    return seconds

def makeTime(seconds):
    time = Time()
    time.seconds = seconds%60
    time.minutes = (seconds/60)%60
    time.hours = seconds/3600
    return time

def addTime(t1, t2):
    seconds = convertToSeconds(t1) + convertToSeconds(t2)
    return makeTime(seconds)

def after(t1, t2):
    if convertToSeconds(t1) > convertToSeconds(t2):
        return 1
    else:
        return 0

# Figure out why following function doesn't work as expected:
def increment(time, seconds):
    time = addTime(time, makeTime(seconds))

inTime = Time()
inTime.hours = input("Hours:  ")
inTime.minutes = input("Minutes:  ")
inTime.seconds = input("Seconds:  ")

inSeconds = input("Seconds to add to given time:  ")

increment(inTime, inSeconds)

print "The time is now:  ",
printTime(inTime)

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