For the lab this week, you will write a program that randomly generates math problems like “3 * 4 + 10” and counts how many of these questions a person can answer correctly in a fixed amount of time (say 30 seconds).
Half of this prelab is experimenting and there is nothing to hand in for these parts (“Guessing game” and “Infinite loops”). For the “Timing” section, answer the two questions (labeled “Question 1” and “Question 2”) on Gradescope.
Look at the Python functions we
discussed in class, particularly the number_guessing_game function. Play with
it a few times and then look at the code and make sure you understand what it
is doing. We’ve also provided two alternative functions number_guessing_game2
and number_guessing_game3, which behave the same way, but are structured
differently. Look at these variants and make sure you understand those as well.
Any of these ways of implementing this function is a good choice.
Python has a module named time that has a variety of functionality for
working with time, dates, etc. If you’re curious, you can check out the
documentation. In
this lab, we’ll be experimenting with the time function within this module.
This function returns the number of seconds that have elapsed since a
particular date and time. For example, this code
>>> import time
>>> print(time.time())
will print the number of seconds elapsed since the starting date.
Question 1: Figure out what date the clock started counting on. To do this, convert the number of seconds that have elapsed into the number of days that have elapsed. Then, use an online tool such as Date Calendar or Days from a Date to subtract that number of days from the current date. If you work on this question after 7:00 PM, use tomorrow’s date in the online tool to get the answer exactly correct (the computation uses Universal Time Coordinated, which is 5 hours ahead of Eastern Standard Time).
We won’t be using them right now, but there are other functions that allow you to
get the current time in a more human friendly way. You can look at the
documentation for the time module for more information.
Elapsed time from an arbitrary time/date may not seem that useful. However, we
can easily figure out how long a particular activity takes with that data.
We first invoke time() and record how many seconds have elapsed in a
variable, then, at some later point after some time has elapsed, invoke
time() again and record the result in another variable. If we take the
difference between these two time readings, we get the time elapsed.
Question 2: Write a sequence of Python statements that uses the
input function to ask the user for their name, measures how long it
takes them to enter their name, then prints out how many seconds
elapsed. You’ll have to record the time before and after the user
enters the text.
for loops run for a fixed number of iterations and so we don’t have to worry
about them not finishing. With a while loop, however, if the Boolean loop
condition never becomes False then the loop will never end. For example, the
following is an infinite loop and will never end:
while True:
print("hello")
In Thonny, create a new file and enter this text, then run the program. What happens? What should happen? (These are rhetorical questions, not to hand in as part of your prelab :-)
Most likely you’ll see a lot of “hello” appear in the Shell. To stop the program, click into the console window, then type Ctrl-c (Control + c). It might take a while to respond, but you should get your prompt back eventually. If Ctrl-c doesn’t work, you can also click on the red “stop sign” icon at the top of Thonny. This will “restart” the Shell process terminating the current computation.
Remember these ways of stopping a program in case you introduce an infinite loop by mistake. If your program doesn’t print anything in the loop, it might just appear to hang, and you’ll have to interrupt it as described above.