User interaction via while-loops / jumping out of 2 while loops

Question

Hello fellow programmers,

I'm quite a Python and overall programming newbie and I don't know how to process user input the bestimmt. A friend of mine suggested while loops and they worked quite well but now I have a serious problem.

The program is about asking the user which one of 3 ways to calculate Pi he wants. After his/her selection, e.g. the way to calculate Pi using a polygon which doubles the number of corners after each iteration, it asks how many digit the user wants to see or how many loops should be calculated etc. I also have added some code that checks what the user has written, e.g. if the user is asked to either type y or n but types b the program reminds him of that and asks again.

This style has led to whiles, inside whiles, inside whiles and now looks more like HTML code than Python and is a little complicated to understand...

Take a look:

#!/usr/bin/python
# -*- coding: iso-8859-15 -*-

prgrm_ctrl_main_while_start = 0
while prgrm_ctrl_main_while_start == 0:

    print "Please select the type of algorithm you want to calculate Pi."
    usr_ctrl_slct_algrthm = raw_input("'p' to use polygons, 'm' to use the Monte-Carlo algorithm or 'c' for the Chudnovsky algorithm: ")
    print " "
    if usr_ctrl_slct_algrthm == 'p':

        #import libraries
        import time
        from mpmath import *

        #starting values 
        n_corners = mpf(8)                                                                  
        counter = 0                                                                         
        while_loop_check_itertions = 0
        while while_loop_check_itertions == 0:

            print "Pi will be calculated more precisely the more iterations you select but it'll also take longer!"
            loops = int(input("Please select number of iterations (1 - 10.000.000): "))
            print " "
            if  1 <= loops <=  10000000:
                loops = loops - 1
                decimals = int(input("Please select the amount of decimals you want to see: "))
                print " "
                decimals = decimals + 1
                starttime = time.clock()


                mp.dps = decimals                                                                           


                while counter <= loops:                                                             
                    counter = counter + 1                                                           

                    n_corners = mpf(n_corners) * mpf(2)                                                 

                    circle = mpf(360)                                                           
                    alpha = mpf(circle) / mpf(n_corners)                                    
                    beta = mpf(alpha) / mpf(2)                                              
                    radiansBeta = mpf(mp.radians(beta))                             
                    opp_leg = mpf(mp.sin(radiansBeta))                                                                                                      
                    edge_lngth = mpf(opp_leg) * mpf(2)                                                                                          
                    circmfrnce = mpf(n_corners) * mpf(edge_lngth)                                                       
                    pi = mpf(circmfrnce) / mpf(2)                                                                                           

                    print "Pi: ", mpf(pi)
                    print "Time to calculate: ", time.clock() - starttime, "seconds"
                    print " "
                    prgrm_ctrl_p_algrthm_while_start = 0
                    while prgrm_ctrl_p_algrthm_while_start == 0:
                        usr_ctrl_slct_p_algrthm = raw_input("Would you like to try this algorithm again? (y/n): ")
                        print " "
                        if usr_ctrl_slct_p_algrthm == 'y':
                            usr_ctrl_slct_p_algrthm_slction = 0
                            break
                        elif usr_ctrl_slct_p_algrthm == 'n':
                            usr_ctrl_slct_p_algrthm_slction = 1
                            break
                        else:
                            print "You must either type 'y' or 'n'!"
                            continue
                    if usr_ctrl_slct_p_algrthm_slction == 0:
                        continue
                    else:
                        usr_ctrl_slct_diffrt_algrthm_while_start = 0
                        while usr_ctrl_slct_diffrt_algrthm_while_start == 0:
                            usr_ctrl_slct_diffrt_algrthm = raw_input("Do you want to use another algorithm? (y/n): ")
                            print " "
                            if usr_ctrl_slct_diffrt_algrthm == 'y':
                                usr_ctrl_slct_diffrt_algrthm_slction = 0
                                break
                            elif usr_ctrl_slct_diffrt_algrthm == 'n':
                                print "See you next time!"
                                print " "
                                usr_ctrl_slct_diffrt_algrthm_slction = 1
                                break
                            else:
                                print "You must either type 'y' or 'n'!"
                                continue
                        if usr_ctrl_slct_diffrt_algrthm_slction == 0:               #The program gets to this line and in case of the user selecting 'y' should continue in the first while-loop
                            continue
                        else:                                                       #if the user says 'n' the program should interrupt and stop, in the best case it should close the command line (in my case IDLE)
                            break                                                   #instead of doing all this the code gets executed again in the 2nd while loop not the 1st
        """NOTE: I also know the lines above continue or quit the 2nd while-loop"""

            elif loops < 1:
                print "Please select at least one iteration!"
                while_loop_check_algrthm_slct = 0
                while while_loop_check_algrthm_slct == 0:
                    usr_ctrl_slct_algrthm_p_try_agn = raw_input("Do you want to try it again? (y/n): ")
                    print " "
                    if usr_ctrl_slct_algrthm_p_try_agn == 'y':
                        usr_ctrl_slct_algrthm_p_try_agn_slction = 0
                        break
                    elif usr_ctrl_slct_algrthm_p_try_agn == 'n':
                        usr_ctrl_slct_algrthm_p_try_agn_slction = 1
                        break
                    else:
                        print "You must either type 'y' or 'n'!"
                        continue
                if usr_ctrl_slct_algrthm_p_try_agn_slction == 1:
                    break
                else:
                    continue
            else:
                print "The maximum amount of iterations is 10 million!"
                while_loop_check_algrthm_slct = 0
                while while_loop_check_algrthm_slct == 0:
                    usr_ctrl_slct_algrthm_p_try_agn = raw_input("Do you want to try it again? (y/n): ")
                    print " "
                    if usr_ctrl_slct_algrthm_p_try_agn == 'y':
                        usr_ctrl_slct_algrthm_p_try_agn_slction = 0
                        break
                    elif usr_ctrl_slct_algrthm_p_try_agn == 'n':
                        usr_ctrl_slct_algrthm_p_try_agn_slction = 1
                        break
                    else:
                        print "You must either type 'y' or 'n'!"
                        continue
                if usr_ctrl_slct_algrthm_p_try_agn_slction == 1:
                    break
                else:
                    continue

I have commented the lines that are effected...

I can't solve the problem with the main-while-loop therefore I'm asking you how I can solve this. Is there a better way of handling user input and checking if it's correct? I'm stuck at a point where I wish I had goto because I can't imagine any other solution.

Hopefully you can help me and thank you for reading this long code! I appreciate that! :)

holofox

possible duplicate of [How to break out of multiple loops in Python?](http://stackoverflow.com/questions/189645/how-to-break-out-of-multiple-loops-in-python) — Cody Piersall, Aug 27 '15 at 18:21

score 0 · Answer 1 · edited May 23 '17 at 10:29

0

As Robert Rossney says in an answer to another question:

My first instinct would be to refactor the nested loop into a function and use return to break out.

edited May 23 '17 at 10:29

Community

1
1

answered Aug 27 '15 at 18:22

Cody Piersall

8,312
2
43
57

rolika · Accepted Answer · 2015-09-01T09:29:32.013

0

My first thought is simplify things, please see this "pseudo-code":

while True: #select algorithm type
    #code: ask for algorithm
    if answer not in "pmc":
        #some message
        continue #non-valid algorithm selected, ask again
    #...
    if answer == 'p':
        while True: #select iteration range
            #code: ask for iteration
            if answer_not_in_range:
                #some message
                continue #non-valid iteration value, ask again
            #...
            #perform calculation upon valid selections
            #...
            #calculation ends
            #code: ask for try again with other iteration (algorithm stays same)
            if answer != "yes":
                break #break out of "iteration" loop
            #else loop continues asking for new iteration
    #code: ask for try again with other algorithm
    if answer != "yes":
        break #"algorithm" loop ends, program ends

edited Sep 01 '15 at 09:29

answered Aug 27 '15 at 19:13

rolika

381
1
10

This looks great I'll try to rewrite my code some time. I will let you know if it works :) – Aug 28 '15 at 18:04
Hey @rolika I hope you read this.. I don't get your code after '#...'. Do you want to ask the amount of iterations BEFORE any type of algorithm gets selected? Because normally I would first ask about the type of algorithm with 'if answer == 'p': #code which leaves me to the same problem. Or how did you think to ask the user about the type of algorithm to be used? – Aug 31 '15 at 01:52
1

I think i forgot that if answer == 'p'... Put it after the first #..., and indent the whole second while-loop. – rolika Aug 31 '15 at 06:05
Oh man the code works perfectly! Thank you man. But I still have to figure out how I can check for a correct user input. (Because it seems that the '!=' does not work. E.g. when program is asking for algorithm type and I enter p it prints the input was wrong and asks again?!) Are these operators compatible with python 2? – Aug 31 '15 at 15:06
@holofox, try `if answer not in "pmc":` instead of series of `or`s – rolika Sep 01 '15 at 06:18
Wow! Now it works perfectly. Glad to have people like you around! Thank you for your help you saved my school work. – Sep 01 '15 at 19:21

User interaction via while-loops / jumping out of 2 while loops

2 Answers2