Creating a loop with two variables in Python, where one variable only changes after every nth loop while the other changes with each loop

Question

I'm trying to write a program where I have two lists & one dictionary:

dict = {'fruit1' : 'apple', 'fruit2' :'banana', 'fruit3':'cherry' ....and so on} 
list1 = ['a','b','c','d','e'....]
list2 = ['fruit1', 'fruit2','fruit3'....]

I have a program which looks like this. [This is not right at all, but it helps represent what I'm trying to get as the result].

for obj1 in list1:
    for obj_2 in list2:
        print(obj1)
        print(obj_2)
        print(dict[obj_2])

My need is to loop this in a way where obj_2 changes every nth loop, but obj_1 changes every loop. How can I achieve this? So my result would look like(considering nth loop is 3rd loop):

a
fruit1
apple
b
fruit1
apple
c
fruit1
apple
d
fruit2
banana
e
fruit2
banana
f
fruit2
banana
g
fruit3
cherry
.
.
.

Barmar · Accepted Answer · 2020-08-20 07:31:03Z

1

Use a counter variable instead of nested loops. Increment the counter each time through the loop, and when it reaches n wrap it back to 0 and increment the index into list2.

n = 3
list2_index = 0
counter = 0
for obj1 in list1:
    obj_2 = list2[list2_index]
    print(obj1)
    print(obj_2)
    print(dict[obj_2])
    counter += 1
    if counter == n:
        counter = 0
        list2_index += 1

BTW, don't use dict as a variable name, it's the name of a built-in type.

answered Aug 20, 2020 at 7:31

Barmar

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Comments

EHM · Accepted Answer · 2020-08-20 07:57:32Z

1

so all you have to do to achive is change the place of your two for loops.

#BTW it isn't adviced to use reserved keywords for variable names so dont use Dict for a variable name
myDict = {'fruit1' : 'apple', 'fruit2' :'banana', 'fruit3':'cherry'} 
list1 = ['a','b','c','d','e']
list2 = ['fruit1', 'fruit2','fruit3']

#so in this nested loop obj2 only changs after  the n loops (n being the length of list1)
#which is after list1 is complete and it does that over and over 
#until list2 is complete
for obj2 in list2:
    for obj1 in list1:
        print(obj1)
        print(obj2)
        print(myDict[obj2])

EDIT I might have misunderstood what you meant by third loop as @Barmar suggested. so if that is what you meant here is another piece of code.

myDict = {'fruit1' : 'apple', 'fruit2' :'banana', 'fruit3':'cherry'} 
list1 = ['a','b','c','d','e']
list2 = ['fruit1', 'fruit2','fruit3']

#a variable to keep track of the nth loop
nthLoop = 1 
for obj2 in list2:
    for obj1 in list1:
        #if you print for three times which is what you wanted for your nthloop to be 
        #then break, which will break out of this nested loop allowing to only print 3 times and also set the 
        #nthLoop back to zero so that it will work nicely for the next iteration
        if nthLoop > 3:
            nthLoop = 0
            break
        print(obj1)
        print(obj2)
        print(myDict[obj2])
        nthLoop += 1

edited Aug 20, 2020 at 7:57

answered Aug 20, 2020 at 7:29

EHM

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3 Comments

Barmar Over a year ago

This prints fruit1 apple 5 times, not 3 times.

user14131697 Over a year ago

Thanks for your answer! However, I'm trying to limit the print of "fruit1" to 3 times only, not based on the length of the list1 If we assume the list1 is 26 characters long

EHM Over a year ago

@user14131697 How about now? does the new solution answer your question

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