Analysis of Structures - Baustatik-Info-Server

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Page 38Analysis of Structures - WS10/112.12 Date, Time and TimespanDate and time functions in common are very important and therefor Python supports this with a standardpackage datetime. Within this package you will find some very simple and powerful objects andfunctions.The package is loaded with the following statement. We load from datetime the subpackage datetimeand set the alias name time. The second line shows, how to get the actual time. The datetime objectcontents from the left to the right the year, the month, the day, the hour, the minutes, the seconds andthe microseconds. Because the computer does not support microseconds but milliseconds the measuredmilliseconds are multiplied with the factor 1000.>>> from datetime import datetime as time>>> time.now()datetime.datetime(2010, 11, 4, 19, 25, 33, 15000)To implement some performance checking code it is very useful to have a timespan, which is the differenceof two datetime objects. The timespan object is called timedelta and is as well an object of thedatetime package.If we now want to check the performance of a code snippet, we will implement the following code.First we have to import the datetime package. Then we get the actual time and assign this object to thevariable t1. Then the code to check follows. Within a last step we again create a datetime object callingthe time.now() function and assigning the object to the variable t2. If we subtract t1 from t2 wewill get a timedelta object. The timedelta objects contents the number of days, the number of secondsand the number of microseconds of the time difference.from datetime import datetime as timet1 = time.now()... our code snippet ...t2 = time.now()t3 = t2 -t1print t3>>> datetime.timedelta(0, 12, 906000)If we want to have the time difference in seconds, we have to write a little function, which adds all thistime parts in the unit second. If we suppose, that T is a valid timedelta object, we extract the seconds withthe seconds attribute and assign it to our seconds variable. The next part handles the microseconds.We divide them by 10 6 and add the part to the seconds variable. The last part calculates the seconds ofthe given hours and add this value to our second variable. The value is returned to the caller.def GetTimeSpanInSeconds(T):secs = float(T.seconds)secs += float(T.microseconds)/1.e6secs += float(t.days)*24.*60.*60.return secsOne very important application of the timedelta object is the measurement of a program’s performance.The next example shows how to investigate the performance of the creation of a tuple and the creation ofa list. Here we apply the above discussed function GetTimeSpanInSeconds.Investigating the Creating Time of Tuples and Lists using a Function ApprochE. Baeck
2.12. DATE, TIME AND TIMESPAN Page 39# we need the datetime packagefrom datetime import datetime as time# calculating the timespan in floatsdef GetTimeSpanInSeconds(T):t = float(T.seconds)t+= float(T.microseconds)/1.e6t+= float(T.days)*24.*60.*60return tnX = 100000# number of entities to createT = () # empty tupleL = [] # empty list# create a tuple with nX itemst1 = time.now()for i in range(nX):T += (i,)t2 = time.now()sT = GetTimeSpanInSeconds(t2-t1) # and calculate the timespanprint "Creation of a tuple with %d items: %.3fs" % (nX,sT)# create a list with nX itemst1 = time.now()for i in range(nX):L += [i,]t2 = time.now()sL = GetTimeSpanInSeconds(t2-t1) # and calculate the timespanprint "creation of a list with %d items: %.3fs" % (nX,sL)# convert the list into a tuplet1 = time.now()TL = tuple(L)t2 = time.now()sTL= GetTimeSpanInSeconds(t2-t1) # and calculate the timespanprint "Create tuple from list: %.3fs" % sTLEnd of CodingThe console output on a one year old double processor notebook is given below. You see that it is verywasteful to create a tuple with a lot of items concatenating them with a += operator. On the other hand alist with the some number of items is created in no time. And the conversion of a list into a tuple costsnothing. So we can resume the the creation of a very large tuple should be done by creating a list and2.12.2011
Page 1: Analysis of StructuresBook of Examp
Page 5 and 6: CONTENTS Page 1A.1.5 Moments of Ine
Page 7: Part IProgramming with Python3
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Page 71 and 72: 4Some Aspects and IntroductionIn th
Page 73 and 74: 4.3. A MODELING CHAIN Page 694.3 A
Page 75 and 76: 4.4. A LITTLE INTERACTIVE WARM UP E
Page 77 and 78: 5Scripts and ExamplesIn this chapte
Page 79 and 80: 5.1. 3 TRUSSES SCRIPT Page 75(6) Cr
Page 81 and 82: 5.1. 3 TRUSSES SCRIPT Page 77# (1)
Page 83 and 84: 5.1. 3 TRUSSES SCRIPT Page 79myJob.
Page 85 and 86: 5.2. U PROFILE SCRIPT Page 81prjnam
Page 87 and 88: 5.2. U PROFILE SCRIPT Page 83# - se
Page 89 and 90: 5.2. U PROFILE SCRIPT Page 85# set
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5.2. U PROFILE SCRIPT Page 89Figure
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Part IIIAppendix95
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Index:, 28AbaqusabaqusMacros, 73Bas
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