General

The While Loop

When iterating we generally have no real idea of how long it will last, so a do loop with its set number of iterations doesn't cut the mustard. Instead use a while loop with the ending condition(s) stated. Avoid while True: or the slightly faster while 1: with controlling if clauses, while and its conditions easily takes care of the situation. The only slight problem is to ensure that the loop conditions will run, so the starting conditions should satisfy the first run of the while loop.

Remember that the while conditions are satisfied as the iterations progress, and once the target value is achieved the loop is ended. Compare the conditional part of the if statement and the equivalent while loop:

for x in (mylist):
    .......
    do something
    .......
    if myint > 9:
        break

while myint < 11:
    ........
    do something
    ........

The condition has the opposite sense, the if statement prevents the myint from exceeding the limit whereas while allows myint to increase up to the limit. In both snippets when myint reaches 10 the loop will end.

When setting the condition remember that unless the loop fulfills the condition it will not end, it is safer to add a counter to the condition that stops the loop after a number of iterations with an and operator between the two conditions:

myint = 5
step = 0    # our counter
while myint < 11 and step < 19:
    ........
    do something
    ........
    step += 1   # the counter increases by 1 at the end of the loop

The loop now stops whenever either of the two components in the loop is satisfied. As both condition components are True at initialisation the loop continues to run until one of the conditions is False.

PrettyTable

This module was used extensively in the iterations to produce a tabular display of the relevant variables and their progressive changes. First import the module then setup the table before an interpolation function is called, after the initialisation and before the main loop save the initialisation conditions. At the loop end save the variable values:

from prettytable import PrettyTable

def myfunc(a, b, ...z):
    ........
    myint = 5
    step = 0
    pt.add_row([step, myint, a, ... ,None,... z])
    while myint < 11 and step < 19:
        ........
        do something
        ........
        step += 1
        pt.add_row([step, myint, a, ... z])
    return step, myint, ...

pt = PrettyTable(['step', 'myint', 'a', ... , 'z'])
a = ...
...
z = ...
step, myint, ... = myfunc(a,b,...z)
print(pt)
print('other stuff', ...)

The table setup:

pt = PrettyTable(['step', 'myint', 'a', ... , 'z'])

gives the table column names corresponding to the variable names to be monitored. The first:

pt.add_row([step, myint, a, ... ,None,... z])

add_row command corresponds to the initialisation data, if any column has not yet been computed insert None into that column, so we maintain a place holder. The next add_row command is the main information gathering part, it is placed after the counter has been increased at the end of the loop. All the columns should have information.

PrettyTable is versatile so read its documents to see what else it can do.

Those Pesky Imps

Just in case you were wondering what the skipper has been hopping mad about - it's those implicit equations.