Re: [Tutor] Re Help with this script
Hi Alan, I did not receive personally your last email but I have read it on the forum. OK i understand now what you were talking about, sorry it took such a long time for me to see the solution, the good thing about it is that I am learning tons. I will probably post soon again once I hit a wall on my next exercise. Thanks a million for your help (also Kent and John - I will try to rewrite your poem/exercise once I get a minute, thanks) Regards JC ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Re Help with this script
OK Alan, I thing I have seen the light!!. Almost. :-) - def print_options(): print -- print Options: print a. print options print f. quit the programme print -- print_options() choice = 0 while choice != 'f': print choice = raw_input(Choose an option: ) if choice == 'a': print Here we go again print_options() if choice == 'f': break That should be all you need. print_options() This shouldn't be needed. Is it that if you use while 1: you create a recursive function? Hope I am right. NO the recursive bit is where the function calls itself. In the previous version you had the while loop inside the function so that you called print_options while you were still inside print_options, like this: def print_options(): print -- print Options: print a. print options print f. quit the programme print -- choice = 0 while choice != 'f': print choice = raw_input(Choose an option: ) if choice == 'a': print Here we go again print_options() ## THIS CALL IS INSIDE THE FUNCTION if choice == 'f': break It was the fact that the call was inside the function that made it recursive. When you selected f to quit you simply quit that call to the function and returned to the higher level call and had to select f again until you eventually got back to the top level.. I'll try to draw it: print_options() choice = a print_options() choice = a print_options() choice = a print_options() choice = f choice = f choice = f choice = f exit You needed to select f to exit each call to print_options. Any clearer? Alan G Author of the Learn to Program web tutor http://www.freenetpages.co.uk/hp/alan.gauld ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Re Help with this script
OK Alan, I thing I have seen the light!!. Here is the script that Kent and you asked me to look at modified: - def print_options(): print -- print Options: print a. print options print f. quit the programme print -- print_options() choice = 0 while choice != 'f': print choice = raw_input(Choose an option: ) if choice == 'a': print Here we go again print_options() if choice == 'f': break print_options() - Is it that if you use while 1: you create a recursive function? Hope I am right. Thanks JC PREVIOUS EMAIL OK the situation is that I haven't still found out what the answer is, I have noticed in the other hand that if I select the option a let's say 4 times, I need to enter the option f 4 times. I am curious to know what the solution is. I have read your chapter on recursion but that did not clear anything. OK, basically the problem is that you have unintentionally created a recursive function. Every time you call it you create a new copy of the function. When you exit the function you wind up back in the previous copy. So as many times as you call the function you have to exit it the same number of times to get back to the top of your program. Have a think about it, and see if that makes sense. Alan G Author of the Learn to Program web tutor http://www.freenetpages.co.uk/hp/alan.gauld ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Re Help with this script
Quoting John Carmona [EMAIL PROTECTED]: Is it that if you use while 1: you create a recursive function? Hope I am right. No ... Remember how functions can call other functions? def add(x, y): Add two integers together. return x+y def mul(x, y): Multiply two integers together. if x == 0: return 0 if x 0: x = -x product = y while x 1: product = add(product, y) x = add(x, -1) The mul function calls add to do some of its work for it. A recursive functio nis just a function that calls itself. For example, we could rewrite add as: def increment(x): Increment an integer. return x + 1 def decrement(x): Decrement an integer. return x - 1 def add(x, y): Add two integers together. if x == 0: return y if x == 1: return increment(y) if x == -1: return decrement(y) if x 0: return add(-1, add(add(1, x), y)) else: return add(1, add(add(-1, x), y)) In this case, add is a recursive function, because it makes calls to itself. There's nothing magical about recursive functions or recursion; you just have to be a bit careful to make sure that your program will end. Example: def poem(): print 'A mad metaprogrammer wrote a mad metaprogram,\n which started: ', poem() print 'sort of close, were the words that the programmer finally chose\nTo bring his mad program to some sort of close.' The poem() function will call the poem() function which will call the poem() function which will call the poem() function, with no end in sight... Another example: def qsort(lst): Quicksort a list. if len(lst) = 1: return lst pivot = lst[0] return qsort([x for x in lst if x pivot]) + [pivot] + qsort([x for x in lst if x pivot]) This will stop because the argument in each recursive call to qsort is smaller than the original, and because there is a smallest value ([]). Does this help? [Bonus questions: 1. Can you rewrite the recursive add() so that you only need one of (increment, decrement)? 2. Do you recognise the inspiration for poem()? ] -- John. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Re Help with this script
Hi Alan, sorry for not replying sooner I am right in the middle of setting up a network at home. Thanks for your email. OK the situation is that I haven't still found out what the answer is, I have noticed in the other hand that if I select the option a let's say 4 times, I need to enter the option f 4 times. I am curious to know what the solution is. I have read your chapter on recursion but that did not clear anything. As soon as i get a minute I will look again. Thanks JC ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Re Help with this script
OK the situation is that I haven't still found out what the answer is, I have noticed in the other hand that if I select the option a let's say 4 times, I need to enter the option f 4 times. I am curious to know what the solution is. I have read your chapter on recursion but that did not clear anything. OK, basically the problem is that you have unintentionally created a recursive function. Every time you call it you create a new copy of the function. When you exit the function you wind up back in the previous copy. So as many times as you call the function you have to exit it the same number of times to get back to the top of your program. Have a think about it, and see if that makes sense. Alan G Author of the Learn to Program web tutor http://www.freenetpages.co.uk/hp/alan.gauld ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Re Help with this script
Thanks Kent, as far as I can see I get the same problem that on my script, i need to enter f 3 to 4 times before I exit the programme. Hmmm, why, I can't see it really, i thought that the fact to have the break command would terminate the script straight away. If I enter f first then the programme ends. What am i missing? JC John Carmona wrote: Thanks for the help Kent, Noel and Alan. Here is my final script (it seems to be working ok but sometimes if I select quit the programme, I need to enter that option 2 or 3 times before it works, is this a bug Try this program. Choose option a a few times, then choose f enough times to exit. See if you can figure out what is going on. def print_options(): print -- print Options: print a. print options print f. quit the programme print -- while 1: choice = raw_input(Choose an option: ) if choice == 'a': print 'About to call print_options' print_options() print 'Finished calling print_options' if choice == 'f': break print_options() Kent ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Re Help with this script
can't see it really, i thought that the fact to have the break command would terminate the script straight away. break terminates the current loop, which is inside your print_options function. print_options is called from inside print_options. Research the term recursion and see if you can see where the problem lies. (Try my online tutor for one explanation...) Alan G Author of the Learn to Program web tutor http://www.freenetpages.co.uk/hp/alan.gauld If I enter f first then the programme ends. What am i missing? JC John Carmona wrote: Thanks for the help Kent, Noel and Alan. Here is my final script (it seems to be working ok but sometimes if I select quit the programme, I need to enter that option 2 or 3 times before it works, is this a bug Try this program. Choose option a a few times, then choose f enough times to exit. See if you can figure out what is going on. def print_options(): print -- print Options: print a. print options print f. quit the programme print -- while 1: choice = raw_input(Choose an option: ) if choice == 'a': print 'About to call print_options' print_options() print 'Finished calling print_options' if choice == 'f': break print_options() Kent ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Re Help with this script
Thanks for the help Kent, Noel and Alan. Here is my final script (it seems to be working ok but sometimes if I select quit the programme, I need to enter that option 2 or 3 times before it works, is this a bug (I am running Win XP), please feel free to comment if you thing that something could be improved. Time to do the next exercise. JC #By J Carmona #Programme that compute volumes or surfaces ##First menu is for the calculation of area ##Second menu is for the calculation of volume ##First ask the user what he wants to do running = True def area_rect(): length = input(Length: ) width = input (Width: ) print The area is: ,length*width def area_circ(): radius = input(What is the radius?: ) print The area is approximately: , 3.14159*(radius**2) def area_squ(): side = input (What is the length of one side?: ) print The area is: , side*side def area_tgle(): base = input (What is the base of the triangle?: ) heigth = input (What is the heigth of the triangle?: ) print The area is: ,base*heigth/2 def vol_sph(): radius = input(What is the radius?: ) print The volume is: , (4*3.14159*radius**3)/3 def vol_cube(): side = input(Side: ) print The volume is: ,side**3 def vol_box(): width = input (What is the width of the box?: ) length = input (What is the length of the box?: ) depth = input (What is the depth of the box?: ) print The volume is: , width*length*depth def vol_cone(): radius = input (What is the radiux of the base of the cone?: ) heigth = input (What is the heigth of the cone?: ) print The volume is: , 0.*3.144159*(radius**2)*heigth def task_options(): print --- print Options: print a. Print options: print b. Do you want to calculate areas?: print c. Do you want to calculate volumes?: print d. Quit the programme print --- choice = raw_input(Choose an option: ) if choice == 'a': print task_options() elif choice == 'b': print print_options() elif choice == 'c': print print_options_2() elif choice == 'd': running = False def print_options(): print_options print -- print Options: print a. print options print b. calculate circle area print c. calculate square area print d. calculate rectangle area print e. calculate triangle area print f. quit the programme print -- while 1: choice = raw_input(Choose an option: ) if choice == 'a': print_options() elif choice == 'b': area_circ() elif choice == 'c': area_squ() elif choice == 'd': area_rect() elif choice == 'e': area_tgle() if choice == 'f': break def print_options_2(): print -- print Options: print a. print options print b. calculate the volume of a sphere print c. calculate the volume of a cube print d. calculate the volume of a box print e. calculate the volume of a cone print f. quit the programme print -- while 1: choice = raw_input(Choose an option: ) if choice == 'a': print_options() elif choice == 'b': vol_sph() elif choice == 'c': vol_cube() elif choice == 'd': vol_box() elif choice == 'e': vol_cone() elif choice == 'e': print_options() if choice == 'f': break #Call starting menu task_options() ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Re Help with this script
John Carmona wrote: Thanks for the help Kent, Noel and Alan. Here is my final script (it seems to be working ok but sometimes if I select quit the programme, I need to enter that option 2 or 3 times before it works, is this a bug Try this program. Choose option a a few times, then choose f enough times to exit. See if you can figure out what is going on. def print_options(): print -- print Options: print a. print options print f. quit the programme print -- while 1: choice = raw_input(Choose an option: ) if choice == 'a': print 'About to call print_options' print_options() print 'Finished calling print_options' if choice == 'f': break print_options() Kent ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
