CODEWITHSUNDEEP
pythonpython-3.xlistfor-loop
Kai036
Kai036

Reputation: 310

Change values in a list using a for loop (python)

I currently have some code that reads like this:

letters = {
10 : "A",
11 : "B",
12 : "C",
13 : "D",
14 : "E",
15 : "F"
}
vallist = [rd1, rd2, gd1, gd2, bd1, bd2]
for i in vallist:
    if i >= 10:
        i = letters[i]

What I want to happen is the for loop to iterate through vallist and replace any value that is greater than 10 with its corresponding letter. However, my current code just changes i and not the original value in the list. For example, if rd1 is set to 15, the code runs through and i is set to "F", but rd1 does not change to "F", and instead just stays as 15. How can I fix this?

Upvotes: 9

Views: 35098

Answers (4)

Madfish
Madfish

Reputation: 85

actually i is the reference of that element of array and the value changes will not be affected to that element , instead try this,

# iterating through every index of array

for i in range(len(vallist)):
 if vallist[i] >= 10 and vallist[i]<=15:
      vallist[i] = letters[vallist[i]]

Upvotes: 0

blhsing
blhsing

Reputation: 106553

For each iteration of the for loop the variable i is assigned with just a copy of the value of an item in vallist, so changes made to i won't be reflected in i.

You should update the items of i via index, which you can generate with the enumerate function:

for index, value in enumerate(vallist):
    if value >= 10:
        vallist[index] = letters[value]

Upvotes: 13

Krist&#243;f Varga
Krist&#243;f Varga

Reputation: 168

for i in range(len(vallist)):
    if vallist[i] >= 10:
        vallist[i] = letters[i]

Because in your case i is just a copy of the current item in vallist. But this way i will be an index, so you can modify your original list throught it.

Upvotes: 0

Georges Lorr&#233;
Georges Lorr&#233;

Reputation: 443

rd1, rd2, gd1, gd2, bd1, bd2 = 10, 11, 12, 13, 14, 9
letters = {
10 : "A",
11 : "B",
12 : "C",
13 : "D",
14 : "E",
15 : "F"
}
vallist = [rd1, rd2, gd1, gd2, bd1, bd2]
for index, value in enumerate(vallist):
    if value >= 10 and value <= 15:
        vallist[index] = letters[value]
print(vallist)

As mentioned in the other comment you need both the index and the value while looping over your vallist. so you can replace the value on the index with the value in your dictionary.

Upvotes: 2

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