CODEWITHSUNDEEP
pythonlist
ragardner
ragardner

Reputation: 1975

Python insert number in list sequence

I am trying to insert a number into a list of a sequence of numbers, for some reason this small program just sits there consuming CPU power... no idea why it's not working:

number = 5
lst = [4,5,6]
if all(x > number for x in lst):
    lst.insert(0,number)
elif all(x < number for x in lst):
    lst.append(number)
else:
    for i,v in enumerate(lst):
        if v>number:
            lst.insert(i-1,number)
print (lst)

expected output:

lst = [4,5,5,6]

Upvotes: 0

Views: 2127

Answers (1)

Alan Leuthard
Alan Leuthard

Reputation: 798

Your for loop is inserting the number 5 into the middle of the list a theoretically infinite amount of times (or until you run out of whatever limited resource the list consumes, whichever happens first).

1) for i,v in enumerate(lst):
2)    if v>number:
3)       lst.insert(i-1,number)

On the first pass, line 1 starts the loop with v = 4 and i = 0. Line 2 finds v is not greater than number.

On the second pass, line 1 continues the loop with v = 5 and i = 1. Line 2 is also false.

Third pass, line 1: v = 6, i = 2. Line 2 finds a true statement and moves to line 3. Line 3 inserts the object referenced by number into position i - 1, inserting 5 into position 1 of the list.

At this point the list is:

lst = [4, *5*, **5**, 6]

The italicized 5 is the number you added to the list. The bolded 5 is where the current pointer is, i = 2. Notice that the 6 we just checked got moved forward with the insert.

Fourth pass: v = 6, i = 3. Line 2 finds a true statement and moves to line 3. Line 3 inserts the object referenced by number into position i - 1, inserting 5 into position 2 of the list.

At this point the list is:

lst = [4, 5, *5*, **5**, 6]

etc etc etc.

A quick fix:

for i, v in enumerate(lst):
    if v > number:
        lst.insert(i-1, number)
        **break**

You're just checking for and adding a single number, so break out of the loop once you insert it, since you're done.

Upvotes: 2

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