plotting and more about classes the bar at the top contains the name of the windowin this case "figure the middle section of the window contains the plot generated by the invocation of pylab plot the two parameters of pylab plot must be sequences of the same length the first specifies the -coordinates of the points to be plottedand the second specifies the -coordinates togetherthey provide sequence of four coordinate pairs[( , )( , )( , )( , )these are plotted in order as each point is plotteda line is drawn connecting it to the previous point the final line of codepylab show()causes the window to appear on the computer screen if that line were not presentthe figure would still have been producedbut it would not have been displayed this is not as silly as it at first soundssince one might well choose to write figure directly to fileas we will do laterrather than display it on the screen the bar at the bottom of the window contains number of push buttons the rightmost button is used to write the plot to file the next button to the left is used to adjust the appearance of the plot in the window the next four buttons are used for panning and zooming and the button on the left is used to restore the figure to its original appearance after you are done playing with pan and zoom it is possible to produce multiple figures and to write them to files these files can have any name you likebut they will all have the file extension png the file extension png indicates that the file is in the portable networks graphics format this is public domain standard for representing images in some operating systemspylab show(causes the process running python to be suspended until the figure is closed (by clicking on the round red button at the upper lefthand corner of the windowthis is unfortunate the usual workaround is to ensure that pylab show(is the last line of code to be executed for those of you too young to knowthe icon represents "floppy disk floppy disks were first introduced by ibm in they were inches in diameter and held all of , bytes unlike later floppy disksthey actually were floppy the original ibm pc had single kbyte -inch floppy disk drive for most of the and sfloppy disks were the primary storage device for personal computers the transition to rigid enclosures (as represented in the icon that launched this digressionstarted in the mid- (with the macintosh)which didn' stop people from continuing to call them floppy disks